Tag Archives: General Relativity and Quantum Cosmology

Oscillation properties of relativistic tori in the vicinity of a distorted deformed compact object [CL]

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http://arxiv.org/abs/2209.13471


This paper studies the oscillation properties of relativistic, non-self-gravitating tori in the background of a distorted deformed compact object. This work concentrates on the static and axially symmetric metric containing two quadrupole parameters; relating to the central object and the external fields. This metric may associate the observable effects to these parameters as dynamical degrees of freedom. The astrophysical motivation for choosing such a field is the possibility of constituting a reasonable model for an actual scenario occurring in the vicinity of compact objects. This paper aims to investigate the radial epicyclic frequency in a perfect fluid disk and not a test particle scenario via a local analysis. To achieve this goal, we employ the vertically integrated technique to able to treat the equation analytically. The tori are also modelled with Keplerian and non-Keplerian distributions of specific angular momentum, and we discuss the dependence of oscillation properties on the variable of the model related to angular momentum distribution and quadrupoles. In the present contribution, we further explore these properties with the possibility of relating oscillatory frequencies to some high-frequency quasi-periodic oscillations models and observed data.

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S. Faraji and A. Trova
Wed, 28 Sep 22
73/89

Comments: N/A

The dynamics of Domain Wall Strings [CL]

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http://arxiv.org/abs/2209.12945


We study the dynamics of domain wall solitons in $(2+1)d$ field theories. These objects are extended along one of the spatial directions, so they also behave as strings; hence the name of domain wall strings. We show analytically and numerically that the amount of radiation from the propagation of wiggles on these objects is negligible except for regions of high curvature. Therefore, at low curvatures, the domain wall strings behave exactly as the Nambu-Goto action predicts. We show this explicitly with the use of several different numerical experiments of the evolution of these objects in a lattice. We then explore their dynamics in the presence of internal mode excitations. We do this again by performing field theory simulations and identify an effective action that captures the relevant interactions between the different degrees of freedom living on the string. We uncover a new parametric resonance instability that transfers energy from the internal mode to the position of the domain wall. We show that this instability accelerates the radiation of the internal mode energy. We also explore the possibility of exciting the internal mode of the soliton with the collision of wiggles on the domain wall. Our numerical experiments indicate that this does not happen unless the wiggles have already a wavelength of the order of the string thickness. Finally, we comment on the possible relevance of our findings to cosmological networks of defects. We argue that our results cast some doubts on the significance of the internal modes in cosmological applications beyond a brief transient period right after their formation. This, however, should be further investigated using cosmological simulations of our model.

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J. Blanco-Pillado, D. Jiménez-Aguilar, J. Queiruga, et. al.
Wed, 28 Sep 22
84/89

Comments: 35 pages + appendices, 13 figures

Relativistic Liquids: GENERIC or EIT? [CL]

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http://arxiv.org/abs/2209.12865


We study the GENERIC hydrodynamic theory for relativistic liquids formulated by \”{O}ttinger and collaborators. We use the maximum entropy principle to derive its conditions for linear stability (in an arbitrary reference frame) and for relativistic causality. In addition, we show that, in the linear regime, its field equations can be recast into a symmetric-hyperbolic form. Once rewritten in this way, the linearised field equations turn out to be a particular realization of the Israel-Stewart theory, where some of the Israel-Stewart free parameters are constrained. This also allows us to reinterpret the GENERIC framework in view of the principles of Extended Irreversible Thermodynamics (EIT).

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L. Gavassino and M. Antonelli
Tue, 27 Sep 22
3/89

Comments: 15 pages, no figures. Comments are welcome

Relativistic Liquids: GENERIC or EIT? [CL]

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http://arxiv.org/abs/2209.12865


We study the GENERIC hydrodynamic theory for relativistic liquids formulated by \”{O}ttinger and collaborators. We use the maximum entropy principle to derive its conditions for linear stability (in an arbitrary reference frame) and for relativistic causality. In addition, we show that, in the linear regime, its field equations can be recast into a symmetric-hyperbolic form. Once rewritten in this way, the linearised field equations turn out to be a particular realization of the Israel-Stewart theory, where some of the Israel-Stewart free parameters are constrained. This also allows us to reinterpret the GENERIC framework in view of the principles of Extended Irreversible Thermodynamics (EIT).

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L. Gavassino and M. Antonelli
Tue, 27 Sep 22
3/89

Comments: 15 pages, no figures. Comments are welcome

Primordial black holes and third order scalar induced gravitational waves [CEA]

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http://arxiv.org/abs/2209.12404


The process of \acp{PBH} formation would be inevitably accompanied by \acp{SIGW}. This strong correlation between \acp{PBH} and \acp{SIGW} signals could be a promising approach to detecting \acp{PBH} in the upcoming \ac{GW} experiments, such as \ac{LISA}. We investigate the third order \acp{SIGW} during a \ac{RD} era in the case of a monochromatic primordial power spectrum $\mathcal{P}{\zeta}=A{\zeta}k_\delta\left(k-k_\right)$. For \ac{LISA} observations, the relations between \ac{SNR} and monochromatic primordial power spectrum are studied systematically. It shows that the effects of third order \acp{SIGW} extend the cutoff frequency from $2f_$ to $3f_$ and lead to about $200\%$ increase of the \ac{SNR} for frequency band from $10^{-5}$Hz to $1.6\times 10^{-3}$Hz corresponding to \acp{PBH} with mass range $4\times 10^{-12}M_{\odot} \sim 10^{-7}M_{\odot}$. We find that there exists a critical value $A_=1.76\times 10^{-2}$ for the amplitude of the monochromatic primordial power spectra, such that when $A_{\zeta}>A_$, the energy density of third order \acp{SIGW} will be larger than the energy density of second order \acp{SIGW}.

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Z. Chang, X. Zhang and J. Zhou
Tue, 27 Sep 22
10/89

Comments: N/A

Coupling quintessence kinetics to electromagnetism [CEA]

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http://arxiv.org/abs/2209.12189


We propose a general model where quintessence couples to electromagnetism via its kinetic term. This novelty generalizes the linear dependence of the gauge kinetic function on $\phi$, commonly adopted in the literature. The interaction naturally induces a time variation of the fine-structure constant that can be formulated within a disformally coupled framework. Through a suitable parametrization of the scalar field and the coupling function, we test the model against observations sensitive to the variation of $\alpha$. We undertake a Bayesian analysis to infer the free parameters with data from Earth based, astrophysical and early Universe experiments. We find that the evolution of $\alpha$ is specific to each cosmological era and slows down at late times when dark energy accelerates the Universe. While the most stringent bound on the interaction is obtained from atomic clocks measurements, the quasars provide a constraint consistent with weak equivalence principle tests. This promising model is to be further tested with upcoming and more precise astrophysical measurements, such as those of the ESPRESSO spectrograph.

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B. Barros and V. Fonseca
Tue, 27 Sep 22
21/89

Comments: 15 pages, 9 figures, 2 tables

Relativistic correction to the r-mode frequency in light of multi-messenger constraints [CL]

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http://arxiv.org/abs/2209.11941


R-mode oscillations of rotating neutron stars are promising candidates for continuous gravitational wave (GW) observations. The r-mode frequencies for slowly rotating Newtonian stars are well-known and independent of the equation of state (EOS) but for neutron stars, several mechanisms can alter the r-mode frequency of which the relativistic correction is dominant and relevant for most of the neutron stars. The most sensitive searches for continuous GWs are those for known pulsars for which GW frequencies are in targeted narrow frequency bands of few Hz. In this study, we investigate the effect of several state-of-the-art multi-messenger constraints on the r-mode frequency for relativistic, slowly rotating, barotropic stars. Imposing these recent constraints on the EOS, we find that the r-mode frequency range is slightly higher from the previous study and the narrow band frequency range can increase upto 8-25% for the most promising candidate PSR J0537-6910 depending on the range of compactness. We also derive universal relations between r-mode frequency and dimensionless tidal deformability which can be used to estimate the dynamical tide of the r-mode resonant excitation during the inspiral signal. These results can be used to construct the parameter space for r-mode searches in gravitational wave data and also constrain the nuclear equation of state following a successful r-mode detection.

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S. Ghosh, D. Pathak and D. Chatterjee
Tue, 27 Sep 22
24/89

Comments: 14 Pages,8 Figures, Submitted to ApJ, Comments are welcome

Machine learning constraints on deviations from general relativity from the large scale structure of the Universe [CEA]

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http://arxiv.org/abs/2209.12799


We use a particular machine learning approach, called the genetic algorithms (GA), in order to place constraints on deviations from general relativity (GR) via a possible evolution of Newton’s constant $\mu\equiv G_\mathrm{eff}/G_\mathrm{N}$ and of the dark energy anisotropic stress $\eta$, both defined to be equal to one in GR. Specifically, we use a plethora of background and linear-order perturbations data, such as type Ia supernovae, baryon acoustic oscillations, cosmic chronometers, redshift space distortions and $E_g$ data. We find that although the GA is affected by the lower quality of the currently available data, especially from the $E_g$ data, the reconstruction of Newton’s constant is consistent with both a constant value and with unity within the errors. On the other hand, the anisotropic stress deviates strongly from unity due to the sparsity and the systematics of the $E_g$ data. Finally, we also create synthetic data based on an LSST-like survey and forecast the limits of any possible detection of deviations from GR. In particular we use two fiducial models, namely the cosmological constant model $\Lambda$CDM and a model with an evolving Newton’s constant, and we find that the GA reconstructions of $\mu(z)$ and $\eta(z)$ are in most cases constrained to within a few percent of the fiducial models, thus demonstrating the utility of the GA reconstruction approach.

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G. Alestas, L. Kazantzidis and S. Nesseris
Tue, 27 Sep 22
30/89

Comments: 15 pages, 7 figures, 3 tables, comments welcome

Impact of Rotation on the Multimessenger Signatures of a Hadron-quark Phase Transition in Core-collapse Supernovae [HEAP]

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http://arxiv.org/abs/2209.12418


We study the impact of rotation on the multimessenger signals of core-collapse supernovae (CCSNe) with the occurrence of a first-order hadron-quark phase transition (HQPT). We simulate CCSNe with the \texttt{FLASH} code starting from a 20~$M_\odot$ progenitor with different rotation rates, and using the RDF equation of state from \textit{Bastian} 2021 that prescribes the HQPT. Rotation is found to delay the onset of the HQPT and the resulting dynamical collapse of the protocompact star (PCS) due to the centrifugal support. All models with the HQPT experience a second bounce shock which leads to a successful explosion. The oblate PCS as deformed by rotation gives rise to strong gravitational-wave (GW) emission around the second bounce with a peak amplitude larger by a factor of $\sim10$ than that around the first bounce. The breakout of the second bounce shock at the neutrinosphere produces a $\bar{\nu}_e$-rich neutrino burst with a luminosity of serveral 10$^{53}$~erg~s$^{-1}$. In rapidly rotating models the PCS pulsation following the second bounce generates oscillations in the neutrino signal after the burst. In the fastest rotating model with the HQPT, a clear correlation is found between the oscillations in the GW and neutrino signals immediately after the second bounce. In addition, the HQPT-induced collapse leads to a jump in the ratio of rotational kinetic energy to gravitational energy ($\beta$) of the PCS, for which persistent GW emission may arise due to secular nonaxisymmetric instabilities.

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S. Zha and E. O’Connor
Tue, 27 Sep 22
35/89

Comments: 15 pages, 15 figures, multimessenger data available at this https URL

How unique are pulsar wind nebulae models? Implementation of a multi-parameter, automatic fitting for time-dependent spectra [HEAP]

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http://arxiv.org/abs/2209.12397


Due to the computational cost of calculating a great number of variations of the parameters, detailed radiative models of pulsar wind nebulae (PWNe) do not usually contain fitting algorithms. As a consequence, most of the models in the literature are, in fact, qualitative fits based on visual inspection. This is particularly true when complex, time-dependent models are considered. Motivated by improvements in the computational efficiency of the current PWN models that were obtained in the last years, we here explore the inclusion of automatic fitting algorithms into a fully time-dependent model. Incorporating an efficient fitting tool based on the Nelder-Mead algorithm, we blindly find fitting solutions for the Crab nebula and 3C 58 with a time-dependent radiation model to compute the spectral and dynamical evolution of young and middle-aged PWNe. This inclusion allows us, in addition of more faithfully determining the quality of the fit, to tackle whether there exist degeneracy in the selected PWNe models. We find both for Crab and 3C58, that the fits are well determined, and that no other significantly different set of model parameters is able to cope with experimental data equally well. The code is also able to consider the system’s age as a free parameter, recursively determining all other needed magnitudes depending on age accordingly. We use this feature to consider whether a detailed multi-frequency spectra can constrain the nebula age, finding that in fact this is the case for the two PWNe studied.

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J. Martin and D. Torres
Tue, 27 Sep 22
43/89

Comments: 16 pages, 5 figures, 3 tables. Journal of High Energy Astrophysics (JHEAp), in press

A Monte-Carlo based relativistic radiation hydrodynamics code with a higher-order scheme [HEAP]

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http://arxiv.org/abs/2209.12472


We develop a new relativistic radiation hydrodynamics code based on the Monte-Carlo algorithm. In this code, we implement a new scheme to achieve the second-order accuracy in time in the limit of a large packet number for solving the interaction between matter and radiation. This higher-order time integration scheme is implemented in the manner to guarantee the energy-momentum conservation to the precision of the geodesic integrator. The spatial dependence of radiative processes, such as the packet propagation, emission, absorption, and scattering, are also taken into account up to the second-order accuracy. We validate our code by solving various test-problems following the previous studies; one-zone thermalization, dynamical diffusion, radiation dragging, radiation mediated shock-tube, shock-tube in the optically thick limit, and Eddington limit problems. We show that our code reproduces physically appropriate results with reasonable accuracy and also demonstrate that the second-order accuracy in time and space is indeed achieved with our implementation for one-zone and one-dimensional problems.

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K. Kawaguchi, S. Fujibayashi and M. Shibata
Tue, 27 Sep 22
46/89

Comments: 25 pages, 10 figures, submitted to PRD

Gravitational signal propagation in the Double Pulsar studied with the MeerKAT telescope [HEAP]

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http://arxiv.org/abs/2209.11798


The Double Pulsar, PSR J0737-3039A/B, has offered a wealth of gravitational experiments in the strong-field regime, all of which GR has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the Double Pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in future, the SKA can greatly improve the accuracy of current tests and facilitate tests of NLO contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737-3039A, made using the MeerKAT telescope over the last 3 years. The increased timing precision offered by MeerKAT yields a 2 times better measurement of Shapiro delay parameter s and improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16-yr data by a factor of 1.65. These effects include the retardation effect due to the movement of B and the deflection of the signal by the gravitational field of B. We also investigate novel effects which are expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line-of-sight due to latitudinal signal deflection and find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the Double Pulsar system that meets the timing precision expected from future instruments such as the full SKA.

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H. Hu, M. Kramer, D. Champion, et. al.
Tue, 27 Sep 22
50/89

Comments: 13 pages, 13 figures, accepted for publication in A&A

Searching for Gravitational Waves with CMS [CL]

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http://arxiv.org/abs/2209.12024


The idea of searching for gravitational waves using cavities in strong magnetic fields has recently received significant attention. Most concepts foresee moderate magnetic fields in rather small volumes, similar to those which are currently employed for axion-like particle searches. We propose to use the magnet system of the Compact Muon Solenoid (CMS) experiment after the high luminosity phase of the LHC as a key component for a future detector for gravitational waves in the MHz frequency range. In this paper we briefly discuss a possible cavity concept which can be integrated into CMS and additionally provide a first estimation of its possible sensitivity.

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K. Schmieden and M. Schott
Tue, 27 Sep 22
61/89

Comments: 4 pages, 2 figures

Detecting cosmological gravitational waves background after removal of compact binary coalescences in future gravitational wave detectors [CL]

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http://arxiv.org/abs/2209.11877


The improved sensitivity of third generation gravitational wave detectors opens the possibility of detecting the primordial cosmological stochastic gravitational wave background (SGWB). Detection of the cosmological SGWB is facing a novel challenge: it will likely be masked by the foreground generated by a large number of coalescences of compact binary systems consisting of black holes and/or neutron stars. In this paper, we investigate the possibility of reducing this foreground by removing (notching) the individually resolved compact binary signals in time-frequency space. We establish that such an approach could be used to reach the SGWB sensitivity floor defined by the unresolved part of the compact binaries foreground, which we find to be between $\Omega_{\rm GW} \sim (9.1 \times10^{-12} – 8.6\times10^{-11})$ for a frequency independent energy density spectrum and depending on the rate of coalescing binary neutron star systems. Since third-generation gravitational wave detectors will not be able to resolve all compact binaries, the unresolvable component of the compact binaries foreground may limit the SGWB searches with these detectors.

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H. Zhong, R. Ormiston and V. Mandic
Tue, 27 Sep 22
69/89

Comments: 8 pages, 2 figures, 1 table

Non-oscillatory gravitational quasinormal modes and telling tails for Schwarzschild-de Sitter black holes [CL]

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http://arxiv.org/abs/2209.12058


We show that quasinormal spectrum of gravitational perturbations of Schwarzschild – de Sitter black holes contains a new branch of purely imaginary modes. These modes are not algebraically special and we showed that the sum of them form the well-known in the literature exponential asymptotic tail. When the ratio of the event horizon radius to the cosmological horizon vanishes, these quasinormal modes approach modes of empty de Sitter spacetime. Thus, the spectrum consists of the two branches: Schwarzschild branch deformed by the cosmological constant and de Sitter branch deformed by the black hole mass. While the de Sitter branch contains purely imaginary modes only, the oscillatory modes (with nonzero real part) of the Schwarzschild branch can also become purely imaginary for some values of the cosmological constant, for which they approach the algebraically special mode.

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R. Konoplya and A. Zhidenko
Tue, 27 Sep 22
84/89

Comments: 8 pages, 3 figures, revtex

Numerical Test and Analysis of the 2nd Law of Black Hole Thermodynamics with Gravitational-Wave Data from Binary Black Hole Merger Events [CL]

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http://arxiv.org/abs/2209.11683


Gravitational-wave detections of black hole mergers in binary systems offer an excellent opportunity to test the 2nd law of black hole thermodynamics. In this paper, we review how the entropy of any astrophysical black hole is calculated and we use LIGO and VIRGO’s mass and spin data measurements from black hole merger events detected over the past years to perform entropy calculations and numerically test the generalized 2nd law of thermodynamics. Besides, we analyze the mathematical correlation between the black hole merger event’s initial parameters to prove and conclude that the theorem will always hold.

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J. Sonnenberg
Mon, 26 Sep 22
13/62

Comments: N/A

A binary tree approach to template placement for searches for gravitational waves from compact binary mergers [CL]

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http://arxiv.org/abs/2209.11298


We demonstrate a new geometric method for fast template placement for searches for gravitational waves from the inspiral, merger and ringdown of compact binaries. The method is based on a binary tree decomposition of the template bank parameter space into non-overlapping hypercubes. We use a numerical approximation of the signal overlap metric at the center of each hypercube to estimate the number of templates required to cover the hypercube and determine whether to further split the hypercube. As long as the expected number of templates in a given cube is greater than a given threshold, we split the cube along its longest edge according to the metric. When the expected number of templates in a given hypercube drops below this threshold, the splitting stops and a template is placed at the center of the hypercube. Using this method, we generate aligned-spin template banks covering the mass range suitable for a search of Advanced LIGO data. The aligned-spin bank required ~24 CPU-hours and produced 2 million templates. In general, we find that other methods, namely stochastic placement, produces a more strictly bounded loss in match between waveforms, with the same minimal match between waveforms requiring about twice as many templates with our proposed algorithm. Though we note that the average match is higher, which would lead to a higher detection efficiency. Our primary motivation is not to strictly minimize the number of templates with this algorithm, but rather to produce a bank with useful geometric properties in the physical parameter space coordinates. Such properties are useful for population modeling and parameter estimation.

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C. Hanna, J. Kennington, S. Sakon, et. al.
Mon, 26 Sep 22
30/62

Comments: N/A

Excess of lensing amplitude in the Planck CMB power spectrum [CEA]

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http://arxiv.org/abs/2209.11660


Precise measurements of the Planck cosmic microwave background (CMB) angular power spectrum (APS) at small angles have stimulated accurate statistical analyses of the lensing amplitude parameter $A_{L}$. To confirm if it satisfies the value expected by the flat-$\Lambda$CDM concordance model, i.e. $A_{L} = 1$, we investigate the spectrum difference obtained as: the difference of the measured Planck CMB APS and the Planck best-fit $\Lambda$CDM APS model. To know if this residual spectrum corresponds to statistical noise or if it has a hiden signature that can be accounted for with a larger lensing amplitude $A_{L} > 1$, we apply the Ljung-Box statistical test and find, with high statistical significance, that the spectrum difference is not statistical noise. This spectrum difference is then analysed in detail using simulated APS, based on the Planck $\Lambda$CDM best-fit model, where the lensing amplitude is a free parameter. We explore different binnations of the multipole order \,$\ell$\, and look for the best-fit lensing amplitude parameter that accounts for the spectrum difference in a $\chi^2$ procedure. We find that there is an excess of signal that is well explained by a $\Lambda$CDM APS with a non-null lensing amplitude parameter $A_{lens}$, with values in the interval $[0.10,0.29]$ at 68\% confidence level. Furthermore, the lensing parameter in the Planck APS should be $1 + A_{lens} > 1$ at $\sim 3 \sigma$ of statistical confidence. Additionally, we perform statistical tests that confirm the robustness of this result. Important to say that this excess of lensing amplitude, not accounted in the Planck’s flat-$\Lambda$CDM model, could have an impact on the theoretical expectation of large-scale structures formation once the scales where it was detected correspond to these matter clustering processes.

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R. Mokeddem, W. Hipólito-Ricaldi and A. Bernui
Mon, 26 Sep 22
41/62

Comments: N/A

Relativistic force-free models of the thermal X-ray emission in millisecond pulsars observed by NICER [HEAP]

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http://arxiv.org/abs/2209.11674


Several important properties of rotation-powered millisecond pulsars (MSPs), such as their mass-radius ratio, equation of state and magnetic field topology, can be inferred from precise observations and modelling of their X-ray light curves. In the present study, we model the thermal X-ray signals originated in MSPs, all the way from numerically solving the surrounding magnetospheres up to the ray tracing of the emitted photons and the final computation of their light curves and spectra. Our modelled X-ray signals are then compared against a set of very accurate NICER observations of four target pulsars: PSR J0437-4715, PSR J1231-1411, PSR J2124-3358 and PSR J0030+0451. We find very good simultaneous fits for the light curve and spectral distribution in all these pulsars. The magnetosphere is solved by performing general relativistic force-free simulations of a rotating neutron star (NS) endowed with a simple centered dipolar magnetic field, for many different stellar compactness and pulsar misalignments. From these solutions, we derive an emissivity map over the surface of the star, which is based on the electric currents in the magnetosphere. In particular, the emission regions (ERs) are determined in this model by spacelike four-currents that reach the NS. We show that this assumption, together with the inclusion of the gravitational curvature on the force-free simulations, lead to non-standard ERs facing the closed-zone of the pulsar, in addition to other ERs within the polar caps. The combined X-ray signals from these two kinds of ERs (both antipodal) allow to approximate the non-trivial interpulses found in all the target MSPs light curves.

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F. Carrasco, J. Pelle, O. Reula, et. al.
Mon, 26 Sep 22
61/62

Comments: 16 pages, 9 figures

Hybrid metric-Palatini Higgs inflation [CL]

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http://arxiv.org/abs/2209.11051


We propose an extension of the Higgs inflation to the hybrid metric-Palatini gravity, where we introduce non-minimal couplings between Higgs and both the metric-type and the Palatini-type Ricci scalars. We study the inflationary phenomenology of our model and find that slow-roll inflation can be realized in the large-field regime, giving the observationally favored predictions. In particular, the scalar spectral index exhibits an attractor behavior to $n_{\mathrm{s}}\sim 0.964$, while the tensor-to-scalar ratio can take an arbitrary value depending on the non-minimal coupling parameters, with the metric-Higgs limit $r\sim10^{-3}$ being the maximum. We also investigate the unitarity property of our model. As the ultraviolet (UV) cutoff as a low-energy effective field theory (EFT) of this model is significantly lower than the Planck scale due to a strong curvature of field-space, we consider a possible candidate of UV-extended theories with an additional scalar field introduced so as to flatten the field-space in five-dimension. While the field-space can be flatten completely and this approach can lead to a weakly-coupled EFT, we gain an implication that Planck-scale EFT can be only realized in the limit of metric-Higgs inflation. We also discuss generalizations of the model up to mass-dimension four.

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M. He, Y. Mikura and Y. Tada
Fri, 23 Sep 22
2/70

Comments: 17 pages, 1 figure

Tachyonic production of dark relics: a non-perturbative quantum study [CL]

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http://arxiv.org/abs/2209.10945


We study production of dark relics during reheating after the end of inflation in a system consisting of a non-minimally coupled spectator scalar field and the inflaton. We derive a set of renormalized quantum transport equations for the one-point function and the two-point function of the spectator field and solve them numerically. We find that our system can embody both tachyonic and parametric instabilities. The former is an expected result due to the non-minimal coupling, but the latter displays new features driven by a novel interplay of the two-point function with the Ricci scalar. We find that when the parametric instability driven by the two-point function takes place, it dominates the total particle production. The quantitative results are also found to be highly sensitive to the model parameters.

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K. Kainulainen, O. Koskivaara and S. Nurmi
Fri, 23 Sep 22
5/70

Comments: 21 pages, 8 figures

MLGWSC-1: The first Machine Learning Gravitational-Wave Search Mock Data Challenge [IMA]

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http://arxiv.org/abs/2209.11146


We present the results of the first Machine Learning Gravitational-Wave Search Mock Data Challenge (MLGWSC-1). For this challenge, participating groups had to identify gravitational-wave signals from binary black hole mergers of increasing complexity and duration embedded in progressively more realistic noise. The final of the 4 provided datasets contained real noise from the O3a observing run and signals up to a duration of 20 seconds with the inclusion of precession effects and higher order modes. We present the average sensitivity distance and runtime for the 6 entered algorithms derived from 1 month of test data unknown to the participants prior to submission. Of these, 4 are machine learning algorithms. We find that the best machine learning based algorithms are able to achieve up to 95% of the sensitive distance of matched-filtering based production analyses for simulated Gaussian noise at a false-alarm rate (FAR) of one per month. In contrast, for real noise, the leading machine learning search achieved 70%. For higher FARs the differences in sensitive distance shrink to the point where select machine learning submissions outperform traditional search algorithms at FARs $\geq 200$ per month on some datasets. Our results show that current machine learning search algorithms may already be sensitive enough in limited parameter regions to be useful for some production settings. To improve the state-of-the-art, machine learning algorithms need to reduce the false-alarm rates at which they are capable of detecting signals and extend their validity to regions of parameter space where modeled searches are computationally expensive to run. Based on our findings we compile a list of research areas that we believe are the most important to elevate machine learning searches to an invaluable tool in gravitational-wave signal detection.

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M. Schäfer, O. Zelenka, A. Nitz, et. al.
Fri, 23 Sep 22
6/70

Comments: 25 pages, 6 figures, 4 tables, additional material available at this https URL

New cosmological constraints on $f(T)$ gravity in the light of full Planck-CMB and type Ia Supernovae data [CEA]

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http://arxiv.org/abs/2209.11131


We investigate two new observational perspectives in the context of torsional gravitational modification of general relativity, i.e., the $f(T)$ gravity: i) We use Pantheon data of type Ia supernovae motivated by a time variation of the Newton’s constant on the supernovae distance modulus relation, and find that a joint analysis with Baryon Acoustic Oscillations (BAO) and Big Bang Nucleosynthesis (BBN), i.e., Pantheon+BAO+BBN, provides constraints on the effective free parameter of the theory to be well compatible with the $\Lambda$CDM prediction; ii) We present the framework of $f(T)$ gravity at the level of linear perturbations with the phenomenological functions, namely the effective gravitational coupling $\mu$ and the light deflection parameter $\Sigma$, which are commonly used to parameterize possible modifications of the Poisson equation relating the matter density contrast to the lensing and the Newtonian potentials, respectively. We use the available Cosmic Microwave Background (CMB) data sets from the Planck 2018 release to constrain the free parameters of the $f(T)$ gravity and $\Lambda$CDM models. We find that CMB data, and its joint analyses with Pantheon and BAO data constrain the $f(T)$ gravity scenario to be practically indistinguishable from the $\Lambda$CDM model. We obtain the strongest limits ever reported on $f(T)$ gravity scenario at the cosmological level.

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S. Kumar, R. Nunes and P. Yadav
Fri, 23 Sep 22
7/70

Comments: 18 pages, 2 tables, 5 figures

Stationary black holes and stars in the Brans-Dicke theory with $Λ >0$ revisited [CL]

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http://arxiv.org/abs/2209.11011


It was shown a few years back that for the Brans-Dicke theory with a positive cosmological constant $\Lambda$, and a de Sitter or cosmological event horizon in the asymptotic region, not only there exist no non-trivial field configurations, but also the inverse Brans-Dicke parameter $\omega^{-1}$ must be vanishing, thereby essentially reducing the theory to Einstein’s General Relativity. The assumption of the existence of the cosmological horizon was crucial for this proof. However, since the Brans-Dicke field $\phi$, couples directly to the $\Lambda$-term in the energy-momentum tensor as well as in its equation of motion, perhaps it is reasonable to ask : can $\phi$ become strong instead and screen the effect of $\Lambda$ at very large scales, so that the asymptotic de Sitter structure is replaced by some physically acceptable alternative non-singular boundary condition? In this work we analytically argue that under the assumption of any generic asymptotic stationary spacetime structure in the absence of a cosmological event horizon, similar non-existence results hold, as long as the spacetime is free of any naked curvature singularity. We further support this result by providing explicit numerical computations. Thus we conclude that in the presence of a positive $\Lambda$, and for any generic asymptotic spacetime structure free from curvature singularity, a stationary black hole or even a star solution in the Brans-Dicke theory always necessitates $\omega^{-1}=0$, and thereby reducing the theory to General Relativity.

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M. Ali, S. Bhattacharya and S. Kaushal
Fri, 23 Sep 22
17/70

Comments: v1; 10pp, 4 figs

The effects of self-interacting bosonic dark matter on neutron star properties [HEAP]

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http://arxiv.org/abs/2209.10905


We propose a model of asymmetric bosonic dark matter (DM) with self-repulsion mediated by the vector field coupled to the complex scalar particles. By adopting the two-fluid formalism, we study different DM distribution regimes, either, fully condensed inside the core of a star or, otherwise, distributed in a dilute halo around a neutron star (NS). We show that DM condensed in a core leads to a decrease of the total gravitational mass, radius and tidal deformability compared to a pure baryonic star with the same central density, which we will perceive as an effective softening of the equation of state (EoS). On the other hand, the presence of a DM halo increases the tidal deformability and total gravitational mass. As a result, an accumulated DM inside compact stars could mimic an apparent stiffening of strongly interacting matter equation of state and constraints we impose on it at high densities.
From the performed analysis of the effect of DM particles in a MeV-GeV mass-scale, interaction strength, and relative DM fractions inside NSs we obtained a rigorous constraint on model parameters. Finally, we discuss several smoking guns of the presence of DM that are free from the above mentioned apparent modification of the strongly interacting matter equation of state. With this we could be probed with the future astrophysical and gravitational wave (GW) surveys.

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E. Giangrandi, V. Sagun, O. Ivanytskyi, et. al.
Fri, 23 Sep 22
29/70

Comments: 14 pages, 5 figures

Fully data-driven time-delay interferometry with time-varying delays [CL]

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http://arxiv.org/abs/2209.10851


We recently introduced the basic concepts of an approach to filtering strongly laser-noise dominated space-based gravitational-wave data, like LISA’s phase comparison data streams, which does not rely on independent knowledge of a temporal delays pattern in the dominant noise that generates the data. Instead, our automated Principal Component Interferometry (aPCI) approach only assumes that one can produce some linear combinations of the temporally nearby regularly spaced phase measurements, which cancel the laser noise. Then we let the data reveal those combinations, thus providing us with a set of laser-noise-free data channels. Our basic approach relied on the simplifying additional assumption that laser-noise-cancelling data combinations or the filters which lead to the laser-noise-free data streams are time-independent. In LISA, however, these filters will vary as the constellation armlengths evolve. Here, we discuss a generalization of the basic aPCI concept compatible with data dominated by a still unmodeled but slowly varying dominant noise covariance. We find that despite its independence on any model, the aPCI processing successfully mitigates laser frequency noise below the other noise sources level, and that its sensitivity to gravitational waves is the same as the state-of-the-art second-generation time-delay interferometry, up to a 2% error.

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Q. Baghi, J. Baker, J. Slutsky, et. al.
Fri, 23 Sep 22
33/70

Comments: 11 pages, 7 figures

Polarimetric signatures of hot spots in black hole accretion flows [HEAP]

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http://arxiv.org/abs/2209.09931


The flaring events observed in the Sagittarius A* supermassive black hole system can be attributed to the non-homogeneous nature of the near-horizon accretion flow. Bright regions in this flow may be associated with density or temperature anisotropies, so-called “bright spot” or “hot spots”. Such orbiting features may explain observations at infrared wavelengths as well as recent findings at millimeter wavelengths. In this work, we study the emission from an orbiting equatorial bright spot, imposed on a radiatively inefficient accretion flow background, to find polarimetric features indicative of the underlying magnetic field structure and other system variables including inclination angle, spot size, black hole spin, and more. Specifically, we investigate the impact of these parameters on the Stokes Q-U signatures that commonly exhibit a typical double loop (pretzel-like) structure. Our semi-analytical model, describing the underlying plasma conditions and the orbiting spot, is built within the framework of the numerical radiative transfer code ipole, which calculates synchroton emission at 230 GHz. We showcase the wide variety of Q-U loop signatures and the relation between inner and outer loops. For the vertical magnetic field topology, the inner Q-U loop is explained by the suppression of the synchrotron emission as seen by the distant observer. For the radial and toroidal magnetic field topologies, the inner \quloop corresponds to the part of the orbit where the spot it is receding with respect to the observer. Based on our models we conclude that it is possible to constrain the underlying magnetic field topology with an analysis of the Q-U loop geometry, particularly in combination with a circular polarization measurements.

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J. Vos, M. Moscibrodzka and M. Wielgus
Thu, 22 Sep 22
21/65

Comments: Submitted to A&A

Impact of Rastall gravity on mass, radius and sound speed of the pulsar PSR J0740+6620 [HEAP]

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http://arxiv.org/abs/2209.10287


Millisecond pulsars are perfect laboratories to test possible matter-geometry coupling and its physical implications in light of recent Neutron Star Interior Composition Explorer (NICER) observations. We apply Rastall field equations of gravity, where matter and geometry are non-minimally coupled, to Krori-Barua interior spacetime whereas the matter source is assumed to be anisotropic fluid. We show that all physical quantities inside the star can be expressed in terms of Rastall, $\epsilon$, and compactness, $C=2GM/Rc^2$, parameters. Using NICER and X-ray Multi-Mirror (XMM-Newton) X-ray observational constraints on the mass and radius of the pulsar PSR J0740+6620 we determine Rastall parameter to be at most $\epsilon=0.041$ in the positive range. The obtained solution provides a stable compact object, in addition the squared sound speed does not violate the conjectured sound speed $c_s^2\leq c^2/3$ unlike the general relativistic treatment. We note that there is no equations of state are assumed, the model however fits well with linear patterns with bag constants. In general, for $\epsilon>0$, the theory predicts a slightly larger size star in comparison to general relativity for the same mass. This has been explained as an additional force, due to matter geometry coupling, in the hydrodynamic equilibrium equation contributes to partially diminish the gravitational force effect. Consequently, we calculate the maximal compactness as allowed by the strong energy condition to be $C=0.735$ which is $\sim 2\%$ higher than general relativity prediction. Moreover, for surface density at saturation nuclear density $\rho_{\text{nuc}}=2.7\times 10^{14}$ g/cm$^3$ we estimate the maximum mass $M=4 M_\odot$ at radius $R=16$ km.

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W. Hanafy
Thu, 22 Sep 22
43/65

Comments: 16 pages, 11 figures, 2 tables, to appear in ApJ

The halo bias for number counts on the light cone from relativistic N-body simulations [CEA]

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http://arxiv.org/abs/2209.10533


We present the halo number counts and its two-point statistics, the observable angular power spectrum, extracted for the first time from relativistic N-body simulations. The halo catalogues used in this work are built from the relativistic N-body code gevolution, and the observed redshift and angular positions of the sources are computed using a non-perturbative ray-tracing method, which includes all relativistic scalar contributions to the number counts. We investigate the validity and limitations of the linear bias prescription to describe our simulated power spectra. In particular, we assess the consistency of different bias measurements on large scales, and we estimate up to which scales a linear bias is accurate in modelling the data, within the statistical errors. We then test a second-order perturbative bias expansion for the angular statistics, on a range of redshifts and scales previously unexplored in this context, that is $0.4 \le \bar{z} \le 2$ up to scales $\ell_\mathrm{max} \sim 1000$. We find that the angular power spectra at equal redshift can be modelled with high accuracy with a minimal extension of the number of bias parameters, that is using a two-parameter model comprising linear bias and tidal bias. We show that this model performs significantly better than a model without tidal bias but with quadratic bias as extra degree of freedom, and that the latter is inaccurate at $\bar{z} \ge 0.7$. Finally, we extract from our simulations the cross-correlation of halo number counts and lensing convergence. We show that the estimate of the linear bias from this cross-correlation is consistent with the measurements based on the clustering statistics alone, and that it is crucial to take into account the effect of magnification in the halo number counts to avoid systematic shifts in the computed bias.

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F. Lepori, S. Schulz, J. Adamek, et. al.
Thu, 22 Sep 22
47/65

Comments: 28 pages, 16 figures. Comments are welcome

Revisiting Thermal Charge Carrier Refractive Noise in Semiconductor Optics for Gravitational-Wave Interferometers [CL]

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http://arxiv.org/abs/2209.09994


The test masses in next-generation gravitational-wave interferometers may have a semiconductor substrate, most likely silicon. The stochastic motion of charge carriers within the semiconductor will cause random fluctuations in the material’s index of refraction, introducing a noise source called Thermal Charge Carrier Refractive (TCCR) noise. TCCR noise was previously studied in 2020 by Bruns et al., using a Langevin force approach. Here we compute the power spectral density of TCCR noise by both using the Fluctuation-Dissipation theorem (FDT) and accounting for previously neglected effects of the standing wave of laser light which is produced inside the input test mass by its high-reflecting coatings. We quantify our results with parameters from Einstein Telescope, and show that at temperatures of 10 K the amplitude of TCCR noise is up to a factor of $\sqrt{2}$ times greater than what was previously claimed, and from 77 K to 300 K the amplitude is around 5 to 7 orders of magnitude lower than previously claimed when we choose to neglect the standing wave, and is up to a factor of 6 times lower if the standing wave is included. Despite these differences, we still conclude like Bruns et al. that TCCR noise should not be a limiting noise source for next-generation gravitational-wave interferometers.

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H. Siegel and Y. Levin
Thu, 22 Sep 22
54/65

Comments: 7 pages, 1 figure

Generation of gravitational waves in dynamical Chern-Simons gravity [CL]

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http://arxiv.org/abs/2209.10374


We investigate gravitational waves (GWs) generated in a two-field inflationary model with a non-canonical kinetic term, in which the gravitational Chern-Simons term is coupled to a heavy dynamical field. In such a model, primordial GWs experience a period of resonant amplification for some modes. In addition, isocurvature perturbations suffer from a temporary tachyonic instability due to an effective negative mass, which source curvature perturbations, resulting in large induced GWs. These two stochastic gravitational wave backgrounds correspond to different frequency bands, which are expected to be detected by future GW detectors such as SKA, LISA and Taiji.

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Z. Peng, Z. Zeng, C. Fu, et. al.
Thu, 22 Sep 22
58/65

Comments: N/A

Calibration of neutron star natal kick velocities to isolated pulsar observations [HEAP]

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http://arxiv.org/abs/2209.09252


Current prescriptions for supernova natal kicks in rapid binary population synthesis simulations are based on fits of simple functions to single pulsar velocity data. We explore a new parameterization of natal kicks received by neutron stars in isolated and binary systems developed by Mandel & M\”uller, which is based on 1D and 3D supernova simulations and accounts for the physical correlations between progenitor properties, remnant mass, and the kick velocity. We constrain two free parameters in this model using very long baseline interferometry velocity measurements of Galactic single pulsars. We find that the inferred values of natal kick parameters do not differ significantly between single and binary evolution scenarios. The best-fit values of these parameters are $v_{\rm ns} = 520$ km s$^{-1}$ for the scaling pre-factor for neutron star kicks, and $\sigma_{\rm ns}=0.3$ for the fractional stochastic scatter in the kick velocities.

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V. Kapil, I. Mandel, E. Berti, et. al.
Wed, 21 Sep 22
2/68

Comments: 8 pages, 8 figures, 1 table

Causal, stable first-order viscous relativistic hydrodynamics with ideal gas microphysics [CL]

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http://arxiv.org/abs/2209.09265


We present the first numerical analysis of causal, stable first-order relativistic hydrodynamics with ideal gas microphysics, based in the formalism developed by Bemfica, Disconzi, Noronha, and Kovtun (BDNK theory). The BDNK approach provides definitions for the conserved stress-energy tensor and baryon current, and rigorously proves causality, local well-posedness, strong hyperbolicity, and linear stability (about equilibrium) for the equations of motion, subject to a set of coupled nonlinear inequalities involving the undetermined model coefficients (the choice for which defines the “hydrodynamic frame”). We present a class of hydrodynamic frames derived from the relativistic ideal gas “gamma-law” equation of state which satisfy the BDNK constraints, and explore the properties of the resulting model for a series of (0+1)D and (1+1)D tests in 4D Minkowski spacetime. These tests include a comparison of the dissipation mechanisms in Eckart, BDNK, and Muller-Israel-Stewart theories, as well as investigations of the impact of hydrodynamic frame on the causality and stability properties of Bjorken flow, planar shockwave, and heat flow solutions.

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A. Pandya, E. Most and F. Pretorius
Wed, 21 Sep 22
3/68

Comments: 22 pages, 7 figures, to be submitted to PRD

Jet-Inflated Cocoons in Dying Stars: New LIGO-Detectable Gravitational Wave Sources [HEAP]

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http://arxiv.org/abs/2209.09256


Long Gamma-Ray Bursts (LGRBs), the most powerful events in the Universe, are generated by jets that emerge from dying massive stars. Highly beamed geometry and immense energy make jets promising gravitational wave (GW) sources. However, their sub-Hertz GW emission is outside of ground based GW detector (LIGO) frequency band. Using a 3D general-relativistic magnetohydrodynamic simulation of a dying star, we show that jets inflate a turbulent, energetic bubble-cocoon that emits strong quasi-spherical GW emission within the LIGO band, $ 0.1-0.6 $ kHz, over the characteristic jet activity timescale, $ \approx 10-100 $ s. This is the first non-inspiral GW source detectable by LIGO out to hundreds of Mpc, with $ \approx 0.1 – 10 $ detectable events expected during LIGO observing run O4. These GWs are likely accompanied by detectable energetic core-collapse supernova and cocoon electromagnetic emission, making jetted stellar explosions promising multi-messenger sources.

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O. Gottlieb, H. Nagakura, A. Tchekhovskoy, et. al.
Wed, 21 Sep 22
8/68

Comments: N/A

Amplification of the Primordial Gravitational Waves Energy Spectrum by a Kinetic Scalar in $F(R)$ Gravity [CL]

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http://arxiv.org/abs/2209.09781


In this work we consider a combined theoretical framework comprised by $F(R)$ gravity and a kinetic scalar field. The kinetic energy of the scalar field dominates over its potential for all cosmic times, and the kinetic scalar potential is chosen to be small and non-trivial. In this case, we show that the primordial gravitational wave energy spectrum of vacuum $F(R)$ gravity is significantly enhanced and can be detectable in future interferometers. The kinetic scalar thus affects significantly the inflationary era, since it extends its duration, but also has an overall amplifying effect on the energy spectrum of pure $F(R)$ gravity primordial gravitational waves. The form of the signal is characteristic for all these theories, since it is basically flat and should be detectable from all future gravitational wave experiments for a wide range of frequencies, unless some unknown damping factor occurs due to some unknown physical process.

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V. Oikonomou
Wed, 21 Sep 22
19/68

Comments: Astroparticle Physics in press

Samuil Kaplan and the development of astrophysical research at the Lviv University (dedicated to the 100th anniversary of his birth) [CEA]

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http://arxiv.org/abs/2209.09494


Samuil Kaplan (1921-1978) was a productive and famous astrophysicist. He was affiliated with a number of scientific centers in different cities of former Soviet Union. The earliest 13 years of his career, namely in the 1948-1961 years, he worked in Lviv University in Ukraine (then it was called the Ukrainian Soviet Socialist Republic). In the present paper, the Lviv period of his life and scientific activity is described on the basis of archival materials and his published studies. Kaplan arrived in Lviv in June 1948, at the same month when he obtained the degree of Candidate of science. He was a head of the astrophysics sector at the Astronomical Observatory of the University, was a professor of department for theoretical physics as well as the founder and head of a station for optical observations of artificial satellites of Earth. He was active in the organization of the astronomical observational site outside of the city. During the years in Lviv, Kaplan wrote more than 80 articles and 3 monographs in 9 areas. The focus of his interests at that time was on stability of circular orbits in the Schwarzschild field, on white dwarf theory, on space gas dynamics, and cosmic plasma physics, and turbulence, on acceleration of cosmic rays, on physics of interstellar medium, on physics and evolution of stars, on cosmology and gravitation, and on optical observations of Earth artificial satellites. Some of his results are fundamental for development of theory in these fields as well as of observational techniques. The complete bibliography of his works published during the Lviv period is presented. Respective scientific achievements of Samuil Kaplan are reviewed in the light of the current state of research in these areas.

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B. Novosyadlyj, B. Hnatyk, Y. Kulinich, et. al.
Wed, 21 Sep 22
21/68

Comments: 24 pages, 5 figures; accepted for publication in Europian Physical Journal H

A fraction of dark matter fading with early dark energy ? [CEA]

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http://arxiv.org/abs/2209.09685


In pre-recombination early dark energy (EDE) resolutions of the Hubble tension, the rise of Hubble constant value $H_0$ is usually accompanied with the exacerbation of so-called $S_8$ tension. Inspired by the swampland conjecture, we investigate what if a fraction $f_$ of dark matter is coupled to EDE, $m_{cdm}\sim \exp{(-c{|\Delta\phi_{ede}|\over M_{pl}})}$ with $c\sim {\cal O}(1)$. We perform the MCMC analysis for the relevant EDE models with PlanckCMB, BAO, Pantheon and SH0ES dataset, as well as DES-Y1 data, and find that such a fraction helps to alleviate the $S_8$ tension. However, though $c\gtrsim 0.1$ is allowed for a very small $f_$, which suggests that a small fraction of dark matter has ever faded with EDE, $c\sim0$ is also consistent.

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H. Wang and Y. Piao
Wed, 21 Sep 22
25/68

Comments: 23 pages,8figures

Implementation of an efficient Bayesian search for gravitational wave bursts with memory in pulsar timing array data [CL]

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http://arxiv.org/abs/2209.09343


The standard Bayesian technique for searching pulsar timing data for gravitational wave (GW) bursts with memory (BWMs) using Markov Chain Monte Carlo (MCMC) sampling is very computationally expensive to perform. In this paper, we explain the implementation of an efficient Bayesian technique for searching for BWMs. This technique makes use of the fact that the signal model for Earth-term BWMs (BWMs passing over the Earth) is fully factorizable. We estimate that this implementation reduces the computational complexity by a factor of 100. We also demonstrate that this technique gives upper limits consistent with published results using the standard Bayesian technique, and may be used to perform all of the same analyses that standard MCMC techniques can perform.

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J. Sun, P. Baker, A. Johnson, et. al.
Wed, 21 Sep 22
34/68

Comments: 19 pages, 3 figures, 1 table. Submitted to Astrophysical Journal

Evolving morphology of resolved stellar Einstein rings [IMA]

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http://arxiv.org/abs/2209.09534


We consider strong gravitational lensing by nearby stars. Using our wave-optical treatment of lensing by a compact mass, we study Einstein rings that may form around such stellar lenses. These large and bright rings are resolvable by existing instruments. Such lensing events take place in hours or days, with peak light amplification lasting several minutes. Many such events may be predicted using the Gaia astrometric catalogue. Serendipitous discoveries are also possible. Fortuitous alignments can be used to confirm or discover and study exoplanets. For lenses that have dense stellar regions in their background, these events may occur annually or more often, warranting their continuous or recurrent monitoring. Resolved imaging and spectroscopy of the evolving morphology of an Einstein ring offers knowledge about both the lens and the source. The angular size of the Einstein ring amounts to a direct measurement of the lens mass. The changing orientation of the major and minor images of the source offers astrometric information. The event duration helps determine the source’s size. The sky position of planetary lensing events constrains the planet’s orbit. Spectroscopy of the ring allows for direct investigations of the source. The frequency and predictability of these events and the wealth of information that can be obtained by imaging motivate observational campaigns using existing facilities or new instruments dedicated to the search and study of Einstein rings that form around nearby stars. As a specific example, we consider a predicted 2028 lensing of a red giant by $\alpha$ Centauri A.

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S. Turyshev and V. Toth
Wed, 21 Sep 22
56/68

Comments: 26 pages, 10 figures, 2 table

Compact objects in gravity theories [CL]

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http://arxiv.org/abs/2209.09499


We briefly discuss explicit compact object solutions in higher-order scalar-tensor theories. We start by so-called stealth solutions, whose metric are General Relativity (GR) solutions, but accompanied by a non-trivial scalar field, in both spherically-symmetric and rotating cases. The latter then enables to construct an analytic stationary solution of scalar tensor theory which is called disformed Kerr metric. This solution constitutes a measurable departure from the usual Kerr geometry of GR. We finally consider a scalar-tensor theory stemming from a Kaluza-Klein reduction of a higher-dimensional Lovelock theory, and which enables to obtain non-stealth black holes, highly compact neutron stars and finally wormhole solutions.

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A. Bakopoulos, C. Charmousis and N. Lecoeur
Wed, 21 Sep 22
63/68

Comments: 9 pages, 2 figures, conference proceedings : Rencontres de Blois 2022

Discretely Charged Dark Matter in Inflation Models Based on Holographic Space-time [CL]

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http://arxiv.org/abs/2209.08361


The Holographic Space-time (HST) model of inflation has a potential explanation for dark matter as tiny primordial black holes. Motivated by a recent paper of Barrau\cite{barrau} we propose a version of this model where some of the Inflationary Black Holes (IBHs), whose decay gives rise to the Hot Big Bang, carry the smallest value of a discrete symmetry charge. The fraction $f$ of IBHs carrying this charge is difficult to estimate from first principles, but we fix it by requiring that the crossover between radiation and matter domination occurs at the correct temperature $T_{eq} \sim 1 eV = 10^{-28} M_P$. The fraction is small, $f \sim 2\times 10^{-9}$ so we believe this gives an extremely plausible model of dark matter.

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T. T.Banks and W. W.Fischler
Tue, 20 Sep 22
15/81

Comments: 7 pages, 1 Figure

The Merger Rate of Primordial Black Hole-Neutron Star Binaries in Ellipsoidal-Collapse Dark Matter Halo Models [CEA]

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http://arxiv.org/abs/2209.08909


Primordial black holes (PBHs), as a potential macroscopic candidate for dark matter, can encounter other compact objects in dark matter halos because of their random distribution. Besides, the detection of gravitational waves (GWs) related to the stellar-mass black hole-neutron star (BH-NS) mergers raises the possibility that the BHs involved in such events may have a primordial origin. In this work, we calculate the merger rate of PBH-NS binaries within the framework of ellipsoidal-collapse dark matter halo models and compare it with the corresponding results derived from spherical-collapse dark matter halo models. Our results exhibit that ellipsoidal-collapse dark matter halo models can potentially amplify the merger rate of PBH-NS binaries in such a way that it is very close to the range estimated by the LIGO-Virgo observations. While spherical-collapse dark matter halo models cannot justify PBH-NS merger events as consistent results with the latest GW data reported by the LIGO-Virgo collaboration. In addition, we calculate the merger rate of PBH-NS binaries as a function of PBH mass and fraction within the context of ellipsoidal-collapse dark matter halo models. The results indicate that PBH-NS merger events with the mass of $(M_{PBH}\le 5 M_{\odot}, M_{NS}\simeq 1.4 M_{\odot})$ will be consistent with the LIGO-Virgo observations if $f_{PBH}\simeq 1$. We also show that to have at least on $(M_{PBH}\simeq 5 M_{\odot}, M_{NS}\simeq 1.4 M_{\odot})$ event in the comoving volume $1 Gpc^{3}$ annually, ellipsoidal-collapse dark matter halo models constrain the abundance of PBHs as $f_{PBH} \geq 0.1$.

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S. Fakhry, Z. Salehnia, A. Shirmohammadi, et. al.
Tue, 20 Sep 22
22/81

Comments: 8 pages, 3 figures, 1 table, references added

Impact of large-mass constraints on the properties of neutron stars [HEAP]

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http://arxiv.org/abs/2209.08101


The maximum mass of a nonrotating neutron star, $M_{\rm TOV}$, plays a very important role in deciphering the structure and composition of neutron stars and in revealing the equation of state (EOS) of nuclear matter. Although with a large-error bar, the recent mass estimate for the black-widow binary pulsar PSR J0952-0607, i.e. $M=2.35\pm0.17~M_\odot$, provides the strongest lower bound on $M_{\rm TOV}$ and suggests that neutron stars with very large masses can in principle be observed. Adopting an agnostic modelling of the EOS, we study the impact that large masses have on the neutron-star properties. In particular, we show that assuming $M_{\rm TOV}\gtrsim 2.35\,M_\odot$ constrains tightly the behaviour of the pressure as a function of the energy density and moves the lower bounds for the stellar radii to values that are significantly larger than those constrained by the NICER measurements, rendering the latter ineffective in constraining the EOS. We also provide updated analytic expressions for the lower bound on the binary tidal deformability in terms of the chirp mass and show how larger bounds on $M_{\rm TOV}$ lead to tighter constraints for this quantity. In addition, we point out a novel quasi-universal relation for the pressure profile inside neutron stars that is only weakly dependent from the EOS and the maximum-mass constraint. Finally, we study how the sound speed and the conformal anomaly are distributed inside neutron stars and show how these quantities depend on the imposed maximum-mass constraints.

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C. Ecker and L. Rezzolla
Tue, 20 Sep 22
31/81

Comments: 6 pages, 4 figures, 1 appendix

$R^2$ Gravity Effects on the Kinetic Axion Phase Space [CL]

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http://arxiv.org/abs/2209.08339


In this work we consider the effect of an $R^2$ term on the kinetic misalignment axion theory. By using the slow-roll assumptions during inflation and the field equations, we construct an autonomous dynamical system for the kinetic axion, including the effects of the $R^2$ term and we solve numerically the dynamical system. As we demonstrate, the pure kinetic axion attractor is transposed to the right in the field phase space, and it is no longer $(\phi,\dot{\phi})=(\langle \phi \rangle,0)$, but it is $(\phi,\dot{\phi})=(\langle \phi ‘\rangle,0)$, with $\langle \phi ‘\rangle\neq 0$ some non-zero value of the scalar field with $\langle \phi ‘\rangle> \langle \phi \rangle$. This feature indicates that the kinetic axion mechanism is enhanced, and the axion oscillations are further delayed, compared with the pure kinetic axion case. The phenomenological implications on the duration of the inflationary era, on the commencing of the reheating era and the reheating temperature, are also discussed.

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V. Oikonomou
Tue, 20 Sep 22
44/81

Comments: EPL in press

The Effect of Light Deflection by Solar System Objects on High-Precision SKA Astrometry [CL]

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http://arxiv.org/abs/2209.08702


We have computed the deflection angles caused by 195 objects in the solar system, including 177 satellites and eight asteroids. Twenty-one satellites and six asteroids can bend light from distant compact extragalactic sources by more than 0.1 $\mu$as, and fourteen satellites and the asteroid Ceres can deflect light by more than 1.0 $\mu$as. We calculated the zones and durations of perturbations posed by the gravitational fields of five planets (excluding Earth, Jupiter, and Saturn), Pluto, and Ceres, where the perturbations would affect astrometry measured with the Squared Kilometre Array (SKA). Perturbed zones with deflection angles larger than 0.1 and 1.0 $\mu$as appear as ribbons. Their widths range from dozens of degrees for Uranus, Neptune, and Venus to several degrees or less for other objects at 0.1 $\mu$as, and from $\sim$ 16$^{\circ}$ for Venus to several degrees or less for other objects at 1.0 $\mu$as. From the calculated perturbation durations, the influence of the gravitational fields of selected objects can be divided into four levels: hardly affect SKA astrometry (I), may have little effect (II), may have a great effect (III) on single-epoch astrometry, and may greatly affect both single- and multi-epoch astrometry (IV). The objects corresponding to these levels are Ceres (I), Pluto (II), Mercury and Mars (III), and other objects (IV).

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Y. Li, Y. Xu, S. Bian, et. al.
Tue, 20 Sep 22
48/81

Comments: 10 figures, 5 tables, accepted by ApJ

Null test for cosmic curvature using Gaussian process [CEA]

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http://arxiv.org/abs/2209.08502


The cosmic curvature $\Omega_{K,0}$, which determines the spatial geometry of the universe, is an important parameter in modern cosmology. Any deviation from $\Omega_{K,0}=0$ would have a profound impact on primordial inflation paradigm and fundamental physics. In this work, we adopt a model-independent method to test whether $\Omega_{K,0}$ deviates from zero. We use the Gaussian process to reconstruct the reduced Hubble parameter $E(z)$ and the derivative of distance $D'(z)$ from observational data, and then determine $\Omega_{K,0}$ with a null test relation. The cosmic chronometer (CC) Hubble data, baryon acoustic oscillation (BAO) Hubble data, and supernovae Pantheon sample are considered. Our result is consistent with a spatially flat universe within the domain of reconstruction $0<z<2.3$, at the $1\sigma$ confidence level. In the redshift interval $0<z<1$, the result favors a flat universe, while at $z>1$, it tends to favor a closed universe. In this sense, there is still a possibility for a closed universe. We also carry out the null test of the cosmic curvature at $0<z<4.5$ using the simulated gravitational wave standard sirens, CC+BAO and redshift drift Hubble data. The result shows that in the future, with the synergy of multiple high-quality observations, we can tightly constrain the spatial geometry or exclude the flat universe.

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P. Wu, J. Qi and X. Zhang
Tue, 20 Sep 22
49/81

Comments: 10 pages, 4 figures

The Effect of Stars on the Dark Matter Spike Around a Black Hole: A Tale of Two Treatments [GA]

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http://arxiv.org/abs/2209.08105


We revisit the role that gravitational scattering off stars plays in establishing the steady-state distribution of collisionless dark matter (DM) around a massive black hole (BH). This is a physically interesting problem that has potentially observable signatures, such as $\gamma-$rays from DM annihilation in a density spike. The system serves as a laboratory for comparing two different dynamical approaches, both of which have been widely used: a Fokker-Planck treatment and a two-component conduction fluid treatment. In our Fokker-Planck analysis we extend a previous analytic model to account for a nonzero flux of DM particles into the BH, as well as a cut-off in the distribution function near the BH due to relativistic effects or, further out, possible DM annihilation. In our two-fluid analysis, following an approximate analytic treatment, we recast the equations as a “heated Bondi accretion” problem and solve the equations numerically without approximation. While both the Fokker-Planck and two-fluid methods yield basically the same DM density and velocity dispersion profiles away from the boundaries in the spike interior, there are other differences, especially the determination of the DM accretion rate. We discuss limitations of the two treatments, including the assumption of an isotropic velocity dispersion.

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S. Shapiro and D. Heggie
Tue, 20 Sep 22
50/81

Comments: 12 pages, 6 figures

Isotropic cosmic birefringence from early dark energy [CEA]

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http://arxiv.org/abs/2209.07804


A tantalizing hint of isotropic cosmic birefringence has been found in the $E B$ cross-power spectrum of the cosmic microwave background (CMB) polarization data with a statistical significance of $3\sigma$. A pseudoscalar field coupled to the CMB photons via the Chern-Simons term can explain this observation. The same field may also be responsible for early dark energy (EDE), which alleviates the so-called Hubble tension. Since the EDE field evolves significantly during the recombination epoch, the conventional formula that relates $E B$ to the difference between the $E$- and $B$-mode auto-power spectra is no longer valid. Solving the Boltzmann equation for polarized photons and the dynamics of the EDE field consistently, we find that currently favored parameter space of the EDE model yields a variety of shapes of the $EB$ spectrum, which can be tested by CMB experiments.

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K. Murai, F. Naokawa, T. Namikawa, et. al.
Mon, 19 Sep 22
15/50

Comments: 6 pages, 3 figures, 1 table

Odd-parity perturbations in the most general scalar-vector-tensor theory [CL]

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http://arxiv.org/abs/2209.07555


In the context of the most general scalar-vector-tensor theory, we study the stability of static spherically symmetric black holes under linear odd-parity perturbations. We calculate the action to second order in the linear perturbations to derive a master equation for these perturbations. For this general class of models, we obtain the conditions of no-ghost and Laplacian instability. Then, we study in detail the generalized Regge-Wheeler potential of particular cases to find their stability conditions.

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Y. Baez and M. Gonzalez-Espinoza
Mon, 19 Sep 22
19/50

Comments: 22 pages, Mathematica Notebook

Gravitational waves from primordial scalar and tensor perturbations [CEA]

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http://arxiv.org/abs/2209.07693


We investigate the second order gravitational waves induced by the primordial scalar and tensor perturbations during radiation-dominated era. The explicit expressions of the power spectra of the second order GWs are presented. We calculate the energy density spectra of the second order GWs for a monochromatic primordial power spectra. For large $k$ $\left( k>k_* \right)$, the effects of the primordial tensor perturbation with tensor-to-scalar ratio $r=A_{h}/A_{\zeta}=0.2$ lead to an around $50\% $ increase of the signal-to-noise ratio (SNR) for LISA observations.

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Z. Chang, X. Zhang and J. Zhou
Mon, 19 Sep 22
29/50

Comments: N/A

Lower bound on the cosmological constant from the classicality of the Early Universe [CL]

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http://arxiv.org/abs/2209.07914


We use the quantum unimodular theory of gravity to relate the value of the cosmological constant, $\Lambda$, and the energy scale for the emergence of cosmological classicality. The fact that $\Lambda$ and unimodular time are complementary quantum variables implies a perennially quantum Universe should $\Lambda$ be zero (or, indeed, fixed at any value). Likewise, the smallness of $\Lambda$ puts an upper bound on its uncertainty, and so a lower bound on the unimodular clock’s uncertainty or the cosmic time for the emergence of classicality. Far from being the Planck scale, classicality arises at around $7 \times 10^{11}$ GeV for the observed $\Lambda$, and taking the region of classicality to be our Hubble volume. We confirm this argument with a direct evaluation of the wavefunction of the Universe in the connection representation for unimodular theory. Our argument is robust, with the only leeway being in the comoving volume of our cosmological classical patch, which should be bigger than that of the observed last scattering surface. Should it be taken to be the whole of a closed Universe, then the constraint depends weakly on $\Omega_k$: for $-\Omega_k < 10^{-3}$ classicality is reached at $ > 4 \times 10^{12}$ GeV. If it is infinite, then this energy scale is infinite, and the Universe is always classical within the minisuperspace approximation. It is a remarkable coincidence that the only way to render the Universe classical just below the Planck scale is to define the size of the classical patch as the scale of non-linearity for a red spectrum with the observed spectral index $n_s = 0.967(4)$ (about $10^{11}$ times the size of the current Hubble volume). In the context holographic cosmology, we may interpret this size as the scale of confinement in the dual 3D quantum field theory, which may be probed (directly or indirectly) with future cosmological surveys.

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N. Afshordi and J. Magueijo
Mon, 19 Sep 22
33/50

Comments: 8 pages, 3 figures, comments are welcome

Gravity assist as a test of relativistic gravity [CL]

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http://arxiv.org/abs/2208.14016


We consider the gravity assist maneuver, that is, a correction of spacecraft motion at its passing near a planet, as a tool for evaluating the Eddington post-Newtonian parameters $\beta$ and $\gamma$, characterizing vacuum spherically symmetric gravitation fields in metric theories of gravity. We estimate the effect of variation in $\beta$ and $\gamma$ on a particular trajectory of a probe launched from the Earth’s orbit and passing closely near Venus, where relativistic corrections slightly change the impact parameter of probe scattering in Venus’s gravitational field. It is shown, in particular, that a change of $10^{-4}$ in $\beta$ or $\gamma$ leads to a shift of about 50 km in the probe’s aphelion position.

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S. Bolokhov, K. Bronnikov and M. Skvortsova
Fri, 16 Sep 22
2/84

Comments: 9 pages, 2 figures

Spin it as you like: the (lack of a) measurement of the spin tilt distribution with LIGO-Virgo-KAGRA binary black holes [HEAP]

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http://arxiv.org/abs/2209.06978


The growing set of gravitational-wave sources is being used to measure the properties of the underlying astrophysical populations of compact objects, black holes and neutron stars. Most of the detected systems are black hole binaries. While much has been learned about black holes by analyzing the latest LIGO-Virgo-KAGRA (LVK) catalog, GWTC-3, a measurement of the astrophysical distribution of the black hole spin orientations remains elusive. This is usually probed by measuring the cosine of the tilt angle ($\cos\tau$) between each black hole spin and the orbital angular momentum, $\cos\tau=+1$ being perfect alignment. Abbott et al. (2021e) has modeled the $\cos\tau$ distribution as a mixture of an isotropic component and a Gaussian component with mean fixed at $+1$ and width measured from the data. In this paper, we want to verify if the data require the existence of such a peak at $\cos\tau=+1$. We use various models for the astrophysical tilt distribution and find that a) Augmenting the LVK model such that the mean of the Gaussian is not fixed at $+1$ returns results that strongly depend on priors. If we allow $\mu>+1$ then the resulting astrophysical $\cos\tau$ distribution peaks at $+1$ and looks linear, rather than Gaussian. If we constrain $-1\leq \mu\leq+1$ the Gaussian component peaks at $\mu=0.47^{+0.47}{-1.04}$ (median and 90\% symmetric credible interval). Two other 2-component mixture models yield $\cos\tau$ distributions that either have a broad peak centered at $0.20^{+0.21}{-0.18}$ or a plateau that spans the range $[-0.5, +1]$, without a clear peak at $+1$. b) All of the models we considered agree on the fact that there is \textit{no} excess of black hole tilts at around $-1$. c) While yielding quite different posteriors, the models considered in this work have Bayesian evidences that are the same within error bars.

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S. Vitale, S. Biscoveanu and C. Talbot
Fri, 16 Sep 22
3/84

Comments: 18 pages including appendices. Zenodo repo will be populated with arxiv v2 at latest

Snowmass 2021 Cosmic Frontier White Paper: The Dense Matter Equation of State and QCD Phase Transitions [HEAP]

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http://arxiv.org/abs/2209.07412


Our limited understanding of the physical properties of matter at ultra-high density, high proton/neutron number asymmetry, and low temperature is presently one of the major outstanding problems in physics. As matter in this extreme state is known to only exist stably in the cores of neutron stars (NSs), complementary measurements from electromagnetic and gravitational wave astrophysical observations of NSs, combined with terrestrial laboratory constraints and further theoretical investigations, hold the promise to provide important insight into the properties of matter in a region of the quantum chromodynamics phase space that is otherwise inaccessible. This multidisciplinary endeavor imposes the following requirements for facilities and resources in the upcoming decade and beyond:
* A next generation of gravitational wave detectors to uncover more double NS and neutron star-black hole mergers;
* Sensitive radio telescopes to find the most massive and fastest spinning NSs;
* Large-area, high-time-resolution and/or high angular resolution X-ray telescopes to constrain the NS mass-radius relation;
* Suitable laboratory facilities for nuclear physics experiments to constrain the dense matter equation of state;
* Funding resources for theoretical studies of matter in this regime;
* The availability of modern large-scale high performance computing infrastructure.
The same facilities and resources would also enable significant advances in other high-profile fields of inquiry in modern physics such as the nature of dark matter, alternative theories of gravity, nucleon superfluidity and superconductivity, as well as an array of astrophysics, including but not limited to stellar evolution, nucleosynthesis, and primordial black holes.

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S. Bogdanov, E. Fonseca, R. Kashyap, et. al.
Fri, 16 Sep 22
6/84

Comments: Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021) under Cosmic Frontier (CF07: Cosmic probes of fundamental physics); 30 pages, 8 figures

Type V singularities with inhomogeneous equations of state [CL]

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http://arxiv.org/abs/2209.07328


Interest in cosmological singularities has remarkably grown in recent times, particularly on future singularities with the discovery of late-time acceleration of the universe and dark energy. Recent work has seen a proper classification of such singularities into strong and weak based on their strength, with weak singularities being the likes of sudden, w and big freeze singularities and strong singularities like the big rip. This has led to a classification of such singularities in various types like Big rip is Type 1, w-singularity is type V etc. While singularities of type I-type IV have been discussed vividly by taking into account inhomogeneous equations of state (EOS), the same has not been attempted for type V singularities. So in this work we have discussed in detail about the formation of type V singularities in various cosmologies after considering inhomogeneous equations of state. We consider two inhomogeneous forms of the EOS in the context of four different cosmological backgrounds ; standard general relativistic cosmology, an asymptotically safe cosmology, a cosmology inspired by modified area-entropy relations, generalized uncertainty principles, holographic renormalization and Chern-Simons gravity( all of which can be coincidentally described by the same form of the modified Friedmann equation) and an f(R) gravity cosmology. We show in detail that one sees some very big differences in the occurence conditions of type V singularities when one makes such considerations. In the particular case of the f(R) gravity cosmology, we see that the type V singularities get completely removed. This work goes to show that the creation and formation of type V singularities is influenced most strongly by the form of the equation of state that one considers, way more so than what background cosmology one chooses.

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O. Trivedi
Fri, 16 Sep 22
13/84

Comments: 19 pages with no figures, comments are very welcome !

Solving nonlinear Klein-Gordon equations on unbounded domains via the Finite Element Method [CL]

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http://arxiv.org/abs/2209.07226


A large class of scalar-tensor theories of gravity exhibit a screening mechanism that dynamically suppresses fifth forces in the Solar system and local laboratory experiments. Technically, at the scalar field equation level, this usually translates into nonlinearities which strongly limit the scope of analytical approaches. This article presents $femtoscope$ $-$ a Python numerical tool based on the Finite Element Method (FEM) and Newton method for solving Klein-Gordon-like equations that arise in particular in the symmetron or chameleon models. Regarding the latter, the scalar field behavior is generally only known infinitely far away from the its sources. We thus investigate existing and new FEM-based techniques for dealing with asymptotic boundary conditions on finite-memory computers, whose convergence are assessed. Finally, $femtoscope$ is showcased with a study of the chameleon fifth force in Earth orbit.

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H. Lévy, J. Bergé and J. Uzan
Fri, 16 Sep 22
27/84

Comments: N/A

A Foreground Model Independent Bayesian CMB Temperature and Polarization Signal Reconstruction and Cosmological Parameter Estimation over Large Angular Scales [CEA]

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http://arxiv.org/abs/2209.07179


Recent CMB observations have resulted in very precise observational data. A robust and reliable CMB reconstruction technique can lead to efficient estimation of the cosmological parameters. We demonstrate the performance of our methodology using simulated temperature and polarization observations using cosmic variance limited future generation PRISM satellite mission. We generate samples from the joint distribution by implementing the CMB inverse covariance weighted internal-linear-combination (ILC) with the Gibbs sampling technique. We use the Python Sky Model (PySM), d4f1s1 to generate the realistic foreground templates. The Synchrotron is parametrized by a spatially varying spectral index, whereas thermal dust is described as two component dust model. We estimate the marginalized densities of CMB signal ${\bf S}$ and theoretical angular power spectrum $C_{\ell}$ utilizing the samples from the entire posterior distribution. The best-fit cleaned CMB map and the corresponding angular power spectrum are consistent with the CMB realization and the sky $C_{\ell}$ implying an efficient foreground minimized reconstruction. The likelihood function $P(C_{\ell}|{\bf D}$) estimated by making use of the Blackwell-Rao estimator is used for the estimation of the cosmological parameters. Our methodology can estimate tensor to scalar ratio $r\ge 0.0075$. Our current work demonstrates an analysis pipeline starting from the reliable estimation of CMB signal and its angular power spectrum to the case of cosmological parameter estimation using the foreground model independent Gibbs-ILC method.

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A. Joseph, U. Purkayastha and R. Saha
Fri, 16 Sep 22
49/84

Comments: N/A

Causal Modifications of Gravity and Their Observational Bounds [CL]

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http://arxiv.org/abs/2209.07525


Since general relativity is the unique theory of massless spin 2 particles at large distances, the most reasonable way to have significant modifications is to introduce one or more light scalars that mediate a new long-range force. Most existing studies of such scalars invoke models that exhibit some kind of “screening” at short distances to hide the force from solar system tests. However, as is well known, such modifications also exhibit superluminality, which can be interpreted as a form of acausality. In this work we explore explicitly subluminal and causal scalar field models. In particular, we study a conformally coupled scalar $\phi$, with a small coupling to matter to obey solar system bounds, and a non-canonical kinetic term $K(X)$ ($X=(\partial\phi)^2/2$) that obeys all subluminality constraints and is hyperbolic. We consider $K(X)$ that is canonical for small $X$, but beyond some nonlinear scale enters a new scaling regime of power $p$, with $1/2<p<1$ (the DBI kinetic term is the limit $p=1/2$ and a canonical scalar is $p=1$). As opposed to screening (and superluminality), this new force becomes more and more important in the regime of high densities (and subluminality). We then turn to the densest environments to put bounds on this new interaction. We compute constraints from precession in binary systems such as Hulse-Taylor, we compute corrections to neutron star hydrostatic equilibrium, and we compute power in radiation, both tensor mode corrections and the new scalar mode, which can be important during mergers.

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M. Hertzberg, J. Litterer and N. Shah
Fri, 16 Sep 22
50/84

Comments: 42 pages, 5 figures

The effect of dynamical tides on gravitational waves from eccentric double white dwarfs [CL]

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http://arxiv.org/abs/2209.07009


The dynamical tide can play an important role in the orbital motion of close eccentric double white dwarf binaries. As the launching of the space-based gravitational-wave detector, the Laser Interferometer Space Antenna (LISA), is just around the corner, detection of gravitational wave signals from such systems is anticipated. In this paper, we discuss the influence of the dynamical tide on eccentric orbits, focusing on the effect on orbital precession. We show that in orbits with a high eccentricity, resonance can cause a large precession when a harmonic of the orbital frequency matches the natural frequencies of the normal modes of the star. In contrast to the case with circular orbits, each mode can encounter multiple resonances with different harmonics and these resonant regions can cover about 10% of the frequency space for orbits with close separations. In this case, the tidal precession effect is distinct from the other contributions and can be identified with LISA if the signal-to-noise ratio is high enough. However, within the highly eccentric-small separation region, the dynamical tide causes chaotic motion and the gravitational wave signal becomes unpredictable. Even not at resonance, the dynamical tide can contribute up to 20% of the precession for orbits close to Roche-lobe filling separation with low eccentricities and LISA can resolve these off-resonant dynamical tide effects within the low eccentricity-small orbital separation region of the parameter space. For lower mass systems, the dynamical tide effect can degenerate with the uncertainties of the eccentricity, making it unmeasurable from the precession rate alone. For higher mass systems, the radiation reaction effect becomes significant enough to constrain the eccentricity, allowing the measurement of the dynamical tide.

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S. Lau, K. Yagi and P. Arras
Fri, 16 Sep 22
55/84

Comments: 13 pages. 9 figures. Submitted to Phys. Rev. D

Testing Modified Gravity Theories with Numerical Solutions of the External Field Effect in Rotationally Supported Galaxies [GA]

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http://arxiv.org/abs/2209.07357


The strong equivalence principle is violated by gravity theories of Milgromian dynamics (MOND) through the action of the external field effect. We test two different Lagrangian theories AQUAL and QUMOND based on their numerical solutions of the external field effect, by comparing two independent estimates of the mean external field strength of the nearby universe: a theory-deduced value from fitting the outer rotation curves of 114 galaxies and an empirical value from the large-scale distribution of cosmic baryons. The AQUAL-deduced external field strength from rotation curves agrees with that from the large-scale cosmic environment, while QUMOND-deduced value is somewhat higher. This suggests that AQUAL is likely to be preferred over QUMOND as an effective non-relativistic limit of a potential relativistic modified gravity theory.

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K. Chae, F. Lelli, H. Desmond, et. al.
Fri, 16 Sep 22
56/84

Comments: 6 pages, 2 figures, 1 table

Improving agnostic searches of Gravitational Waves from Neutron Star instabilities using image filtering [IMA]

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http://arxiv.org/abs/2209.07276


In this paper I present a method to enhance the search sensitivity for long transient Gravitational Waves produced by Neutron Star instabilities. This method consists in a selective image filter, called Triangular Filter, to be applied to data spectrograms. It is shown that thanks to this implementation a 20% gain in sensitivity is achievable.

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L. Pierini
Fri, 16 Sep 22
61/84

Comments: Accepted in Proceedings of the International Astronomical Union, Volume 15 Issue 363

Dynamics of ultrarelativistic charged particles with strong radiation reaction. I. Aristotelian equilibrium state [CL]

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http://arxiv.org/abs/2209.07469


Previous studies from the astrophysics and laser physics communities have identified an interesting phenomenon wherein ultrarelativistic charged particles experiencing strong radiation reaction tend to move along special directions fixed by the local electromagnetic field. In the relativity literature these are known as the “principal null directions” (PNDs) of the Maxwell field. A particle in this regime has “Aristotelian” dynamics in the sense that its velocity (rather than acceleration) is determined by the local field. We study this Aristotelian equilibrium in detail, starting from the Landau-Lifshitz equation describing charged particle motion including radiation reaction. Using a Frenet-Serret frame adapted to the PNDs, we derive the Lorentz factor describing motion along the local PND, together with drift velocities reflecting slower passage from one PND to another. We derive conditions on the field configuration that are necessary for such an equilibrium to occur. We demonstrate agreement of our analytic formulas with full numerical solutions of the Landau-Lifshitz equation in the appropriate regime.

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Y. Cai, S. Gralla and V. Paschalidis
Fri, 16 Sep 22
62/84

Comments: N/A

Constraining Interacting Dark Energy Models from Future Generation PICO and DESI Missions [CEA]

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http://arxiv.org/abs/2209.07167


The next-generation CMB satellite missions are expected to provide robust constraints on a wide range of cosmological parameters with unprecedented precision. But these constraints on the parameters could weaken if we do not attribute dark energy to a cosmological constant. The cosmological models involving interaction between dark energy and dark matter can give rise to comparable energy densities at the present epoch, thereby alleviating the so-called cosmic coincidence problem. In the present paper, we perform a forecast analysis to test the ability of the future generation high-sensitive Cosmic Microwave Background (CMB), and Baryon Acoustic Oscillation (BAO) experiments to constrain phenomenological interacting dark energy models. We consider cosmic variance limited future CMB polarization experiment PICO along with BAO information from the DESI experiment to constrain the parameters of the interacting dark sector. Based on the stability of the cosmological perturbations, we consider two possibilities for the interaction scenario. We investigate the impact of both the coupling constant and the equation of state parameter of dark energy on the CMB temperature power spectrum, matter power spectrum, and $f\sigma_8$. We have used simulated temperature and polarization data from PICO within the multipole ranges ($\ell = 2 – 4000$), and as expected, we do see PICO alone produces better constraints than Planck on the $\Lambda$CDM parameters. With the integration of the PICO and DESI missions, we observe a significant improvement in the constraints on several cosmological parameters, especially the equation of state parameter of dark energy. However, we note that additional data is required to constrain a small positive coupling constant.

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A. Joseph and R. Saha
Fri, 16 Sep 22
63/84

Comments: N/A

Revisiting the Schönberg-Chandrasekhar limit in post main sequence stellar evolution [SSA]

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http://arxiv.org/abs/2209.07389


The Sch\”{o}nberg-Chandrasekhar limit in post main sequence evolution for stars of masses in the range $1.4\lesssim M/M_{\odot}\lesssim 6$ gives the maximum pressure that the stellar core can withstand, once the central hydrogen is exhausted. It is usually expressed as a quadratic function of $1/\alpha$, with $\alpha$ being the ratio of the mean molecular weight of the core to that of the envelope. Here, we revisit this limit in scenarios where the pressure balance equation in the stellar interior may be modified, and in the presence of small stellar pressure anisotropy, that might arise due to several physical phenomena. Using numerical analysis, we derive a three parameter dependent master formula for the limit, and discuss various physical consequences. As a byproduct, in a limiting case of our formula, we find that in the standard Newtonian framework, the Sch\”{o}nberg-Chandrasekhar limit is best fitted by a polynomial that is linear, rather than quadratic, to lowest order in $1/\alpha$.

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S. Chowdhury and T. Sarkar
Fri, 16 Sep 22
72/84

Comments: 12 Pages, 5 figures

Slow-roll inflation in $f(Q)$ non-metric gravity [CL]

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http://arxiv.org/abs/2209.06670


We discuss the cosmological inflation in the context of $f(Q)$ non-metric gravity, where $Q$ is the non-metric scalar. After introducing conformal transformations for $f(Q)$ gravity, we first focus on the potential-slow-roll inflation by studying the corresponding potentials for different forms of the function $f(Q)$ in the Einstein frame. Secondly, we investigate the Hubble-slow-roll inflation for three classes of inflationary potentials considered for the specific form $f(Q)\propto Q^{2}$, in the Jordan frame. We compare results in both approaches with observations coming from Planck and BICEP2/Keck array satellites. Observational constraints on the parameters space of the models are obtained as well.

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S. Capozziello and M. Shokri
Thu, 15 Sep 22
4/67

Comments: 18 pages, 7 figures, accepted for publication ion Physics of the Dark Universe

Kerr black holes with synchronised Proca hair: lensing, shadows and EHT constraints [CL]

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http://arxiv.org/abs/2209.06237


We investigate the gravitational lensing by spinning Proca stars and the shadows and lensing by Kerr black holes (BHs) with synchronised Proca hair, discussing both theoretical aspects and observational constraints from the Event Horizon Telescope (EHT) M87* and Sgr A* data. On the theoretical side, this family of BHs interpolates between Kerr-like solutions — exhibiting a similar optical appearance to that of Kerr BHs — to very non-Kerr like solutions, exhibiting exotic features such as cuspy shadows, egg-like shadows and ghost shadows. We interpret these features in terms of the structure of the fundamental photon orbits, for which different branches exist, containing both stable and unstable orbits, with some of the latter not being shadow related. On the observational side, we show that current EHT constraints are compatible with all such BHs that could form from the growth of the superradiant instability of Kerr BHs. Unexpectedly, given the (roughly) 10% error bars in the EHT data — and in contrast to their scalar cousin model –, some of the BHs with up to 40% of their energy in their Proca hair are compatible with the current data. We estimate the necessary resolution of future observations to better constrain this model.

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I. Sengo, P. Cunha, C. Herdeiro, et. al.
Thu, 15 Sep 22
12/67

Comments: 36 pages, 20 figures + appendix

From the gates of the abyss: Frequency- and polarization-dependent lensing of gravitational waves in strong gravitational fields [CL]

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http://arxiv.org/abs/2209.06459


The propagation of gravitational waves can be described in terms of null geodesics by using the geometrical optics approximation. However, at large but finite frequencies the propagation is affected by the spin-orbit coupling corrections to geometrical optics, known as the gravitational spin Hall effect. Consequently, gravitational waves follow slightly different frequency- and polarization-dependent trajectories. We study the potential for detection of the gravitational spin Hall effect in hierarchical triple black hole systems, consisting of an emitting binary orbiting a more massive body, acting as a gravitational lens. We calculate the difference in time of arrival with respect to the geodesic propagation and find that it follows a simple power law dependence on frequency with a fixed exponent. We calculate the gravitational spin Hall-corrected waveform and its mismatch with respect to the original waveform. The waveform carries a measurable imprint of the strong gravitational field if the source, lens and observer are sufficiently aligned or for generic observers if the source is close enough to the lens. We demonstrate that the gravitational spin Hall effect can be detected, providing an interesting avenue to probe general relativity and the environments of compact binary systems.

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M. Oancea, R. Stiskalek and M. Zumalacárregui
Thu, 15 Sep 22
15/67

Comments: 20 pages, 14 figures

Cosmic searches for Lorentz invariance violation [HEAP]

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http://arxiv.org/abs/2209.06531


Cosmic messengers (gamma rays, cosmic rays, neutrinos and gravitational waves) provide a powerful complementary way to search for Lorentz invariance violating effects to laboratory-based experiments. The long baselines and high energies involved make Cherenkov telescopes, air-shower arrays, neutrino telescopes and gravitational wave detectors unique tools to probe the expected tiny effects that the breaking of Lorentz invariance would cause in the propagation of these messengers, in comparison with the standard scenario. In this chapter we explain the expected effects that the mentioned detectors can measure and summarize current results of searches for Lorentz violation.

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C. Heros and T. Terzić
Thu, 15 Sep 22
33/67

Comments: To appear as a chapter in the book “Modified and Quantum Gravity – From Theory to Experimental Searches on All Scales”, C. L\”ammerzahl and C. Pfeifer editors. Springer Nature

Ultra Long-Term Cosmology and Astrophysics [CEA]

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http://arxiv.org/abs/2209.06572


We examine astronomical observations that would be achievable over a future timeline corresponding to the documented history of human civilization so far, $\sim 10^4$ years. We examine implications for measurements of the redshift drift, evolution of the CMB, and cosmic parallax. A number of events that are rare on the scale of centuries will become easily observable on a timescale $\sim 10^4$ years. Implications for several measurements related to gravity are discussed.

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R. Scherrer and A. Loeb
Thu, 15 Sep 22
45/67

Comments: 4 pages, no figures

Squeezing ${\boldsymbol f_{\rm NL}}$ out of the matter bispectrum with consistency relations [CEA]

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http://arxiv.org/abs/2209.06228


We show how consistency relations can be used to robustly extract the amplitude of local primordial non-Gaussianity ($f_{\rm NL}$) from the squeezed limit of the matter bispectrum, well into the non-linear regime. First, we derive a non-perturbative relation between primordial non-Gaussianity and the leading term in the squeezed bispectrum, revising some results present in the literature. This relation is then used to successfully measure $f_{\rm NL}$ from $N$-body simulations. We discuss the dependence of our results on different scale cuts and redshifts. Specifically, the analysis is strongly dependent on the choice of the smallest soft momentum, $q_{\rm min}$, which is the most sensitive to primordial bispectrum contributions, but is largely independent of the choice of the largest hard momentum, $k_{\rm max}$, due to the non-Gaussian nature of the covariance. We also show how the constraints on $f_{\rm NL}$ improve at higher redshift, due to a reduced off-diagonal covariance. In particular, for a simulation with $f_{\rm NL} = 100$ and a volume of $(2.4 \text{ Gpc}/h)^3$, we measure $f_{\rm NL} = 98 \pm 12$ at redshift $z=0$ and $f_{\rm NL} = 97 \pm 8$ at $z=0.97$. Finally, we compare our results with a Fisher forecast, showing that the current version of the analysis is satisfactorily close to the Fisher error. We regard this as a first step towards the realistic application of consistency relations to constrain primordial non-Gaussianity using observations.

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S. Goldstein, A. Esposito, O. Philcox, et. al.
Thu, 15 Sep 22
50/67

Comments: 16 pages, 8 figures

Black hole hierarchical growth efficiency and mass spectrum predictions [HEAP]

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http://arxiv.org/abs/2209.05766


Hierarchical mergers in bound gravitational environments can explain the presence of black holes with masses greater than $\sim 100 M_{\odot}$. Evidence for this process is found in the third LIGO-Virgo-KAGRA gravitational-wave transient catalog (GWTC-3). We study the efficiency with which hierarchical mergers can produce higher and higher masses using a simple model of forward evolution of binary black hole populations in gravitationally bound systems like stellar clusters. The model relies on pairing probability and initial mass functions for the black hole population, along with numerical relativity fitting formulas for the mass, spin and kick speed of the merger remnant. If unequal mass pairing is disfavored, we show that the retention probability decreases significantly with later generations of the binary black hole population. Our model also predicts the distribution of masses of each black hole merger generation. We find that two of the subdominant peaks in the GWTC-3 component mass spectrum are consistent with second and third generation mergers in dense environments. With more binary black hole detections, our model can be used to infer the black hole initial mass function and pairing probability exponent.

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P. Mahapatra, A. Gupta, M. Favata, et. al.
Wed, 14 Sep 22
6/90

Comments: 12 pages, 4 figures, 1 table

A Systematic Error in the Internal Friction Measurement of Coatings for Gravitational Waves Detectors [IMA]

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http://arxiv.org/abs/2209.06106


Low internal friction coatings are key components of advanced technologies such as optical atomic clocks and high-finesse optical cavity and often lie at the forefront of the most advanced experiments in Physics. Notably, increasing the sensitivity of gravitational-wave detectors depends in a very large part on developing new coatings, which entails developing more suitable methods and models to investigate their loss angle. In fact, the most sensitive region of the detection band in such detectors is limited by the coating thermal noise, which is related to the loss angle of the coating. Until now, models which describe only ideal physical properties have been adopted, wondering about the use of one or more loss angles to describe the mechanical properties of coatings. Here we show the presence of a systematic error ascribed to inhomogeneity of the sample at its edges in measuring the coating loss angle. We present a model for disk-shaped resonators, largely used in loss angle measurements, and we compare the theory with measurements showing how this systematic error impacts on the accuracy with which the loss model parameters are known.

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A. Amato, D. Lumaca, E. Cesarini, et. al.
Wed, 14 Sep 22
25/90

Comments: N/A

On the response of the Einstein Telescope to Doppler anisotropies [CL]

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http://arxiv.org/abs/2209.05770


We study the response function of the Einstein Telescope to kinematic Doppler anisotropies, which represent one of the guaranteed properties of the stochastic gravitational wave background. If the frequency dependence of the stochastic background changes slope within the detector frequency band, the Doppler anisotropic contribution to the signal can not be factorized in a part depending on frequency, and a part depending on direction. For the first time, we study the detector response function to Doppler anisotropies without making any factorizable Ansatz. Moreover, we do not assume that kinematic effects are small, and we derive general formulas valid for any relative velocity among frames. We apply our findings to three well-motivated examples of background profiles: power-law, broken power-law, and models with a resonance motivated by primordial black hole scenarios. We derive the signal-to-noise ratio associated with an optimal estimator for the detection of non-factorizable kinematic anisotropies, and we study it for representative examples.

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D. Chowdhury, G. Tasinato and I. Zavala
Wed, 14 Sep 22
27/90

Comments: 19+9 pages, 10 figures

Building post-Newtonian neutron stars [CL]

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http://arxiv.org/abs/2209.05871


Owed to their compactness, neutron stars involve strong gravity and extreme density physics. Nevertheless, at present, there are a variety of problems where progress (at least conceptually) can be made in the context of weak gravity. Motivated by this we examine how accurately one can model neutron stars using the post-Newtonian approximation to general relativity. In general, we find there is a significant degree of freedom in how the post-Newtonian equations of stellar structure can be formulated. We discuss this flexibility in the formulation and provide examples to demonstrate the impact on stellar models. We also consider the (closely related) problem of building neutron stars using isotropic coordinates. In this context, we provide a new strategy for solving the equations (based on a scaling argument) which significantly simplifies the problem.

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N. Andersson, F. Gittins, S. Yin, et. al.
Wed, 14 Sep 22
39/90

Comments: 23 pages, 7 figures, RevTeX format

From inflation to black hole mergers and back again: Gravitational-wave data-driven constraints on inflationary scenarios with a first-principle model of primordial black holes across the QCD epoch [CEA]

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http://arxiv.org/abs/2209.05959


Recent population studies have searched for a subpopulation of primordial black holes (PBHs) in the gravitational-wave (GW) events so far detected by LIGO/Virgo/KAGRA (LVK), in most cases adopting a phenomenological PBH mass distribution. When deriving such population from first principles in the standard scenario, however, the equation of state of the Universe at the time of PBH formation may strongly affect the PBH abundance and mass distribution, which ultimately depend on the power spectrum of cosmological perturbations. Here we improve on previous population studies on several aspects: (i) we adopt state-of-the-art PBH formation models describing the collapse of cosmological perturbations across the QCD epoch; (ii) we perform the first Bayesian multi-population inference on GW data including PBHs and directly using power spectrum parameters instead of phenomenological distributions; (iii) we critically confront the PBH scenario with LVK phenomenological models describing the GWTC-3 catalog both in the neutron-star and in the BH mass ranges, also considering PBHs as subpopulation of the total events. Our results confirm that LVK observations prevent the majority of the dark matter to be in the form of stellar mass PBHs. We find that the best fit PBH model can comprise a small fraction of the total events, in particular it can naturally explain events in the mass gaps. If the lower mass-gap event GW190814 is interpreted as a PBH binary, we predict that LVK should detect up to a few subsolar mergers and one to $\approx 30$ lower mass gap events during the upcoming O4 and O5 runs. Finally, mapping back the best-fit power spectrum into an ultra slow-roll inflationary scenario, we show that the latter predicts detectable PBH mergers in the LVK band, a stochastic GW background detectable by current and future instruments, and may include the entirety of dark matter in asteroid-mass PBHs.

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G. Franciolini, I. Musco, P. Pani, et. al.
Wed, 14 Sep 22
54/90

Comments: 41 pages, 21 figures

Emergent universe: tensor perturbations within the CSL framework [CL]

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http://arxiv.org/abs/2209.05637


We calculate the primordial power spectrum of tensor perturbations, within the emergent universe scenario, incorporating a version of the Continuous Spontaneous Localization (CSL) model as a mechanism capable of: breaking the initial symmetries of the system, generating the perturbations, and also achieving the quantum-to-classical transition of such perturbations. We analyze how the CSL model modifies the characteristics of the B-mode CMB polarization power spectrum, and we explore their differences with current predictions from the standard concordance cosmological model. We have found that, regardless of the CSL mechanism, a confirmed detection of primordial B-modes that fits to a high degree of precision the shape of the spectrum predicted from the concordance $\Lambda$CDM model, would rule out one of the distinguishing features of the emergent universe. Namely, achieving a best fit to the data consistent with the suppression observed in the low multipoles of the angular power spectrum of the temperature anisotropy of the CMB. On the contrary, a confirmed detection that accurately exhibits a suppression of the low multipoles in the B-modes, would be a new feature that could be considered as a favorable evidence for the emergent scenario.

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O. Palermo, M. Ocampo, G. Bengochea, et. al.
Wed, 14 Sep 22
60/90

Comments: 11 pages, 2 figures, 1 appendix. arXiv admin note: text overlap with arXiv:2108.01472

Simulations of PBH formation at the QCD epoch and comparison with the GWTC-3 catalog [CEA]

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http://arxiv.org/abs/2209.06196


The probability of primordial black hole (PBH) formation is known to be boosted during the Quantum Chromodynamics (QCD) crossover due to a slight reduction of the equation of state. This induces a high peak and other features in the PBH mass distribution. But the impact of this variation during the PBH formation has been so far neglected. In this work we simulate for the first time the formation of PBHs by taking into account the varying equation of state at the QCD epoch, compute the over-density threshold using different curvature profiles and find that the resulting PBH mass distributions are significantly impacted. The expected merger rate distributions of early and late PBH binaries is comparable to the ones inferred from the GWTC-3 catalog for dark matter fractions in PBHs within $0.1 < f_{\rm PBH} <1 $. The distribution of gravitational-wave events estimated from the volume sensitivity could explain mergers around $30-50 M_\odot$, with asymmetric masses like GW190814, or in the pair-instability mass gap like GW190521. However, none of the considered cases leads to a multi-modal distribution with a secondary peak around $8-15 M_\odot$, as suggested by the GWTC-3 catalog, possibly pointing to a mixed population of astrophysical and primordial black holes.

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A. Escrivà, E. Bagui and S. Clesse
Wed, 14 Sep 22
85/90

Comments: 41 pages, 18 figures, comments welcome

Stability and Observability of Magnetic Primordial Black Hole-Neutron Star Collisions [HEAP]

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http://arxiv.org/abs/2209.06060


The collision of a primordial black hole with a neutron star results in the black hole eventually consuming the entire neutron star. However, if the black hole is magnetically charged, and therefore stable against decay by Hawking radiation, the consequences can be quite different. Upon colliding with a neutron star, a magnetic black hole very rapidly comes to a stop. For large enough magnetic charge, we show that this collision can be detected as a sudden change in the rotation period of the neutron star, a glitch or anti-glitch.We argue that the magnetic primordial black hole, which then settles to the core of the neutron star, does not necessarily devour the entire neutron star; the system can instead reach a long-lived, quasi-stable equilibrium. Because the black hole is microscopic compared to the neutron star, most stellar properties remain unchanged compared to before the collision. However, the neutron star will heat up and its surface magnetic field could potentially change, both effects potentially observable.

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J. Estes, M. Kavic, S. Liebling, et. al.
Wed, 14 Sep 22
88/90

Comments: 16 pages, 5 figures

How to delay death and look further into the future if you fall into a black hole [CL]

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http://arxiv.org/abs/2209.04823


In this note, we present a pedagogical illustration of peculiar properties of motion in the vicinity and inside black holes. We discuss how a momentary impulse can modify the lifetime of an object radially falling into a Schwarzschild black hole down to singularity. The well known upper limit for a proper time spent within a horizon, in fact, requires an infinitely powerful kick. We calculate the proper time interval (perceived as personal lifetime of a falling observer) till the contact with the singularity, as well as the time interval in the Lema\^itre frame (which reflects how far into the future of the outer world a falling observer can look), for different values of the kick received by the falling body. We discuss the ideal strategy to increase both time intervals by the engine with a finite power.
This example is suitable for university seminars for undergraduate students specializing in General Relativity and related astrophysical subjects.

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A. Toporensky and S. Popov
Tue, 13 Sep 22
6/85

Comments: 13 pages with 2 figures, accepted for publication in Resonance

Self-gravitating disks around rapidly spinning, tilted black holes: General relativistic simulations [HEAP]

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http://arxiv.org/abs/2209.04454


We perform general relativistic simulations of self-gravitating black hole-disks in which the spin of the black hole is significantly tilted ($45^\circ$ and $90^\circ$) with respect to the angular momentum of the disk and the disk-to-black hole mass ratio is $16\%-28\%$. The black holes are rapidly spinning with dimensionless spins up to $\sim 0.97$. These are the first self-consistent hydrodynamic simulations of such systems, which can be prime sources for multimessenger astronomy. In particular tilted black hole-disk systems lead to: i) black hole precession; ii) disk precession and warping around the black hole; iii) earlier saturation of the Papaloizou-Pringle instability compared to aligned/antialigned systems, although with a shorter mode growth timescale; iv) acquisition of a small black-hole kick velocity; v) significant gravitational wave emission via various modes beyond, but as strong as, the typical $(2,2)$ mode; and vi) the possibility of a broad alignment of the angular momentum of the disk with the black hole spin. This alignment is not related to the Bardeen-Petterson effect and resembles a solid body rotation. Our simulations suggest that any electromagnetic luminosity from our models may power relativistic jets, such as those characterizing short gamma-ray bursts. Depending on the black hole-disk system scale the gravitational waves may be detected by LIGO/Virgo, LISA and/or other laser interferometers.

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A. Tsokaros, M. Ruiz, S. Shapiro, et. al.
Tue, 13 Sep 22
7/85

Comments: N/A

Self-force regularization of a point particle for generic orbits in Kerr spacetime: electromagnetic and gravitational cases [CL]

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http://arxiv.org/abs/2209.05450


The self-force is the leading method in modelling waveforms for extreme mass ratio inspirals, a key target of ESA’s future space-based gravitational wave detector LISA. In modelling these systems, one approximates the smaller body as a point particle leading to problematic singularities that need to be removed. Modelling of this singular structure has settled on the Detweiler-Whiting singular field as the gold standard. As a solution to the governing wave equation itself, on removal, it leaves a smooth regular field that is a solution to the homogeneous wave equation, much like its well established flat spacetime counterpart. The mode-sum method enables subtraction of this singularity mode by mode via a spherical harmonic decomposition. The more modes one has, the faster the convergence in the $\ell$-sum, making these expressions highly beneficial, especially considering the heavy computational burden of waveform production. Until recently, only the two leading orders were known for generic orbits in Kerr spacetime. In a previous paper, we produced the next non-zero parameter for a scalar charged particle in curved spacetime, laying the groundwork for the electromagnetic and gravitational case which we present here.

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A. Heffernan
Tue, 13 Sep 22
14/85

Comments: 11 pages

Gravitational waves from rapid structure formation on microscopic scales before matter-radiation equality [CEA]

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http://arxiv.org/abs/2209.04970


The existence of scalar fields can be probed by observations of stochastic gravitational waves. Scalar fields mediate attractive forces, usually stronger than gravity, on the length scales shorter than their Compton wavelengths, which can be non-negligible in the early universe, when the horizon size is small. These attractive forces exhibit an instability similar to the gravitational instability, only stronger. They can, therefore, lead to the growth of structures in some species. We identify a gravitational waves signature of such processes and show that it can be detected by the future gravitational waves experiments.

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M. Flores, A. Kusenko and M. Sasaki
Tue, 13 Sep 22
18/85

Comments: 7 pages, 1 figure

Multimessenger Picture of J1048+7143 [HEAP]

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http://arxiv.org/abs/2209.05107


We draw the multimessenger picture of J1048+7143, a flat-spectrum radio quasar known to show quasi-periodic oscillations in the $\gamma$-ray regime. We generate the adaptively-binned Fermi Large Area Telescope light curve of this source above 168 MeV to find three major $\gamma$-ray flares of the source, such that all three flares consist of two-two sharp sub-flares. Based on radio interferometric imaging data taken with the Very Large Array, we find that the kpc-scale jet is directed towards west, while our analysis of $8.6$-GHz very long baseline interferometry data, mostly taken with the Very Long Baseline Array, revealed signatures of two pc-scale jets, one pointing towards east, one pointing towards south. We suggest that the misalignment of the kpc- and pc-scale jets is a revealing signature of jet precession. We also analyze the $5$-GHz total flux density curve of J1048+7143 taken with the Nanshan(Ur) and RATAN-600 single dish radio telescopes and find two complete radio flares, slightly lagging behind the $\gamma$-ray flares. We model the timing of $\gamma$-ray flares as signature of the spin-orbit precession in a supermassive black hole binary, and find that the binary could merge in the next $\sim 60-80$ years. We show that both the Pulsar Timing Arrays and the planned Laser Interferometer Space Antenna lack sensitivity and frequency coverage to detect the hypothetical supermassive black hole binary in J1048$+$7143. We argue that the identification of sources similar to J1048+7143 plays a key role to reveal periodic high-energy sources in the distant Universe.

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E. Kun, I. Jaroschewski, A. Ghorbanietemad, et. al.
Tue, 13 Sep 22
27/85

Comments: 16 pages, 8 figures, 2 tables. Submitted to ApJ

SIGWfast: a python package for the computation of scalar-induced gravitational wave spectra [CEA]

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http://arxiv.org/abs/2209.05296


SIGWfast is a python code to compute the scalar-induced gravitational wave spectrum from a primordial scalar power spectrum that can be given in analytical or numerical form. SIGWfast was written with the aim of being easy to install and use, and to produce results fast, typically in a matter of a few seconds. To this end the code employs vectorization techniques within python, but there is also the option to compile a C++ module to perform the relevant integrations, further accelerating the computation. The python-only version should run on all platforms that support python 3. The version employing the C++ module is only available for Linux and MacOS systems.

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L. Witkowski
Tue, 13 Sep 22
32/85

Comments: 16 pages, 4 figures

The Cosmological Black Hole [CL]

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http://arxiv.org/abs/2209.04813


We briefly review the recent novel solution of General Relativity, we call the cosmological black hole, firstly discovered in [Roupas, Z. Eur. Phys. J. C 82, 255 (2022)]. A dark energy universe and a Schwartzschild black hole are matched on a common dual event horizon which is finitely thick due to quantum indeterminacy. The system gets stabilized by a finite tangential pressure applied on the dual horizon. The fluid entropy of the system at a Tolman temperature identified with the cosmological horizon temperature is calculated to be equal with the Bekenstein-Hawking entropy.

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Z. Roupas
Tue, 13 Sep 22
41/85

Comments: Talk given in the 11th International Conference on Mathematical Modelling in Physical Sciences

Probing our Universe's Past Using Earth's Geological and Climatological History and Shadows of Galactic Black Holes [CL]

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http://arxiv.org/abs/2209.04669


In this short review, we discuss how Earth’s climatological and geological history and also how the shadows of galactic black holes might reveal our Universe’s past evolution. Specifically we point out that a pressure singularity that occurred in our Universe’s past might have left its imprint on Earth’s geological and climatological history and on the shadows of cosmological black holes. Our approach is based on the fact that the $H_0$ tension problem may be resolved if some sort of abrupt physics change occurred in our Universe $70-150\,$Myrs ago, an abrupt change that deeply affected the Cepheid parameters. We review how such an abrupt physics change might have been caused in our Universe by a smooth passage of it through a pressure finite-time singularity. Such finite-time singularities might occur in modified gravity and specifically in $F(R)$ gravity, so we show how modified gravity might drive this type of evolution, without resorting to peculiar cosmic fluids or scalar fields. The presence of such a pressure singularity can distort the elliptic trajectories of bound objects in the Universe, causing possible geological and climatological changes on Earth, if its elliptic trajectory around the Sun might have changed. Also, such a pressure singularity affects directly the circular photon orbits around supermassive galactic black holes existing at cosmological redshift distances, thus the shadows of some cosmological black holes at redshifts $z\leq 0.01$, might look different in shape, compared with the SgrA* and M87* supermassive black holes. This feature however can be checked experimentally in the very far future.

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V. Oikonomou, P. Tsyba and O. Razina
Tue, 13 Sep 22
51/85

Comments: Invited article accepted in the journal Universe, special issue ”Modified Gravity Approaches to the Tensions of LCDM”

Axisymmetric, stationary collisionless gas configurations surrounding black holes [CL]

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http://arxiv.org/abs/2209.05327


The properties of a stationary gas cloud surrounding a black hole are discussed, assuming that the gas consists of collisionless, identical massive particles that follow spatially bound geodesic orbits in the Schwarzschild spacetime. Several models for the one-particle distribution function are considered, and the essential formulae that describe the relevant macroscopic observables, like the current density four-vector and the stress-energy-momentum tensor are derived. This is achieved by rewriting these observables as integrals over the constants of motion and by a careful analysis of the range of integration. In particular, we provide configurations with finite total mass and angular momentum. Differences between these configurations and their nonrelativistic counterparts in a Newtonian potential are analyzed. Finally, our configurations are compared to their hydrodynamic analogues, the “polish doughnuts”.

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C. Gabarrete and O. Sarbach
Tue, 13 Sep 22
54/85

Comments: 28 pages, 19 figures, 1 table

Is there evidence for CIDER in the Universe? [CEA]

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http://arxiv.org/abs/2209.04468


In this work we analyze the full linear behaviour of the constrained interacting dark energy (CIDER) model, which is a conformally coupled quintessence model tailored to mimic a $\Lambda$CDM expansion. We compute the matter and temperature anisotropies power spectra and test the model against recent observational data. We shed light on some particular subtleties of the background behaviour that were not fully captured in previous works, and study the physics of the linear cosmological observables. One novelty found was that matter perturbations are enhanced at large scales when compared with the ones of the standard $\Lambda$CDM. The reason and impact of this trend on the cosmological observables and on the physics of the early Universe are considered. We find that the introduction of the coupling parameter alleviates the $\sigma_8$ tension between early and late time probes although Planck data favours the $\Lambda$CDM limit of the model.

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B. Barros, D. Castelão, V. Fonseca, et. al.
Tue, 13 Sep 22
57/85

Comments: 13 pages, 11 figures, 1 table

A characterization method for low-frequency environmental noise in LIGO [IMA]

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http://arxiv.org/abs/2209.04452


We present a method to characterize the noise in ground-based gravitational-wave observatories such as the Laser Gravitational-Wave Observatory (LIGO). This method uses linear regression algorithms such as the least absolute shrinkage and selection operator (LASSO) to identify noise sources and analyzes the detector output versus noise witness sensors to quantify the coupling of such noise. Our method can be implemented with currently available resources at LIGO, which avoids extra coding or direct experimentation at the LIGO sites. We present two examples to validate and estimate the coupling of elevated ground motion at frequencies below 10 Hz with noise in the detector output.

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G. Valdes, A. Hines, A. Nelson, et. al.
Tue, 13 Sep 22
61/85

Comments: N/A

Priorities in gravitational waveform modelling for future space-borne detectors: vacuum accuracy or environment? [CL]

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http://arxiv.org/abs/2209.04060


In preparation for future space-borne gravitational-wave (GW) detectors, should the modelling effort focus on high-precision vacuum templates or on the the astrophysical environment of the sources? We perform a systematic comparison of the phase contributions caused by 1) known environmental effects in both gaseous and stellar matter backgrounds, or 2) high-order post-Newtonian terms in the evolution of mHz GW sources. We use the accuracy of currently available analytical waveform models as a benchmark and find the following trends: the largest unmodelled contributions are likely environmental for binaries lighter than $\sim 10^7/(1+z)^2$~M${\odot}$, where $z$ is the redshift. Binaries heavier than $\sim 10^8/(1+z)$~M${\odot}$ do not require more accurate waveforms due to low signal-to-noise ratios (SNRs). For high-SNR sources, environmental influences are relevant at low redshift, while high-order vacuum templates are required at $z > 4$. Led by these findings, we argue that including environmental effects in waveform models should be prioritised in order to maximize the science yield of mHz detectors.

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L. Zwick, P. Capelo and L. Mayer
Tue, 13 Sep 22
62/85

Comments: Submitted to MNRAS

An Analytical Study of the Primordial Gravitational-Wave-Induced Contribution to the Large-Scale Structure of the Universe [CEA]

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http://arxiv.org/abs/2209.05329


The imprint of gravitational waves (GWs) on large-scale structures (LSS) is a useful and promising way to detect or to constrain them. Tensor fossils have been largely studied in the literature as an indirect way to detect primordial GWs. In this paper we analyze a new effect induced by primordial GWs: a correction to the density contrast of the underlying matter distribution of LSS, as well as its radiation counterpart, induced by the energy density fluctuation of the gravitational radiation. We perform our derivation of the full analytical solution of the density contrast for waves entering the horizon during radiation dominance. We account for two phases in the radiation era, depending on the main contributor to the perturbed energy density of the Universe. By comparing the density contrast of cold dark matter and radiation — sourced by linear gravitational waves only — we conclude that the former overcomes the latter at some time in the radiation era, a behaviour analogous to their linear counterpart. Then we conclude by discussing the case of density perturbations produced by GWs entering the Hubble radius during the matter era as well as their evolution in the late dark-energy dominated phase.

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P. Bari, D. Bertacca, N. Bartolo, et. al.
Tue, 13 Sep 22
68/85

Comments: 51 pages, 1 figure

The False Alarms induced by Gaussian Noise in Gravitational Wave Detectors [CL]

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http://arxiv.org/abs/2209.05475


Gaussian noise is an irreducible component of the background in gravitational wave (GW) detectors. Although stationary Gaussian noise is uncorrelated in frequencies, we show that there is an important correlation in time when looking at the matched filter signal to noise ratio (SNR) of a template, with a typical autocorrelation time that depends on the template and the shape of the noise power spectral density (PSD). Taking this correlation into account, we compute from first principles the false alarm rate (FAR) of a template in Gaussian noise, defined as the number of occurrences per unit time that the template’s matched filter SNR goes over a threshold $\rho$. We find that the Gaussian FAR can be well approximated by the usual expression for uncorrelated noise, if we replace the sampling rate by an effective sampling rate that depends on the parameters of the template, the noise PSD and the threshold $\rho$. This results in a minimum SNR threshold that has to be demanded to a given GW trigger, if we want to keep events generated from Gaussian noise below a certain FAR. We extend the formalism to multiple detectors and to the analysis of GW events. We apply our method to the GW candidates added in the GWTC-3 catalog, and discuss the possibility that GW200308_173609 and GW200322_091133 could be generated by Gaussian noise fluctuations.

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G. Morras, J. Siles, J. Garcia-Bellido, et. al.
Tue, 13 Sep 22
78/85

Comments: 22 pages, 11 figures

Axisymmetric, stationary collisionless gas clouds trapped in a Newtonian potential [CL]

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http://arxiv.org/abs/2209.05325


The properties of an axisymmetric, stationary gas cloud surrounding a massive central object are discussed. It is assumed that the gravitational field is dominated by the central object which is modeled by a nonrelativistic rotationally-symmetric potential. Further, we assume that the gas consists of collisionless, identical massive particles that follow bound orbits in this potential. Several models for the one-particle distribution function are considered and the essential formulae that describe the relevant macroscopical observables, such as the particle and energy densities, pressure tensor, and the kinetic temperature are derived. The asymptotic decay of the solutions at infinity is discussed and we specify configurations with finite total mass, energy and (zero or non-zero) angular momentum. Finally, our configurations are compared to their hydrodynamic analogs. In an accompanying paper, the equivalent general relativistic problem is discussed, where the central object consists of a Schwarzschild black hole.

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C. Gabarrete and O. Sarbach
Tue, 13 Sep 22
80/85

Comments: 27 pages, 15 figures, 3 tables

Cotton gravity and 84 galaxy rotation curves [CL]

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http://arxiv.org/abs/2209.04055


Recently, as a generalization of general relativity, a gravity theory has been proposed in which gravitational field equations are described by the Cotton tensor. That theory allows an additional contribution to the gravitational potential of a point mass that rises linearly with radius as $\Phi = -GM/r + \gamma r/2$, where $G$ is the Newton constant. The coefficients $M$ and $\gamma$ are the constants of integration and should be determined individually for each physical system. When applied to galaxies, the coefficient $\gamma$, which has the dimension of acceleration, should be determined for each galaxy. This is the same as having to determine the mass $M$ for each galaxy. If $\gamma$ is small enough, the linear potential term is negligible at short distances, but can become significant at large distances. In fact, it may contribute to the extragalactic systems. In this paper, we derive the effective field equation for Cotton gravity applicable to extragalactic systems. We then use the effective field equation to numerically compute the gravitational potential of a sample of 84 rotating galaxies. The 84 galaxies span a wide range, from stellar disk-dominated spirals to gas-dominated dwarf galaxies. We do not assume the radial density profile of the stellar disk, bulge, or gas; we use only the observed data. We find that the rotation curves of 84 galaxies can be explained by the observed distribution of baryons. This is due to the flexibility of Cotton gravity to allow the integration constant $\gamma$ for each galaxy. In the context of Cotton gravity, “dark matter” is in some sense automatically included as a curvature of spacetime. Consequently, even galaxies that have been assumed to be dominated by dark matter do not need dark matter.

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J. Harada
Mon, 12 Sep 22
7/54

Comments: 22 pages, 7 figures, 1 table, accepted for publication in Phys. Rev. D

Quasiclassical model of inhomogeneous cosmology [CL]

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http://arxiv.org/abs/2209.04429


Fluctuation terms and higher moments of a quantum state imply corrections to the classical equations of motion that may have implications in early-universe cosmology, for instance in the state-dependent form of effective potentials. In addition, space-time properties are relevant in cosmology, in particular when combined with quantum corrections required to maintain general covariance in a consistent way. Here, an extension of previous investigations of static quasiclassical space-time models to dynamical ones is presented, describing the evolution of 1-dimensional space as in the classical Lemaitre–Tolman–Bondi models. The corresponding spatial metric has two independent components, both of which are in general subject to quantum fluctuations. The main result is that individual moments from both components are indeed required for general covariance to be maintained at a semiclassical level, while quantum correlations between the components are less relevant.

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M. Bojowald and F. Hancock
Mon, 12 Sep 22
21/54

Comments: 43 pages, 11 figures

The Laser Interferometer Space Antenna mission in Greece White Paper [CL]

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http://arxiv.org/abs/2209.04358


The Laser Interferometer Space Antenna (LISA) mission, scheduled for launch in the mid-2030s, is a gravitational wave observatory in space designed to detect sources emitting in the millihertz band. LISA is an ESA flagship mission, currently entering the Phase B development phase. It is expected to help us improve our understanding about our Universe by measuring gravitational wave sources of different types, with some of the sources being at very high redshifts $z\sim 20$. On the 23rd of February 2022 we organized the 1$^\mathrm{st}$ {\it LISA in Greece Workshop}. This workshop aimed to inform the Greek scientific and tech industry community about the possibilities of participating in LISA science and LISA mission, with the support of the Hellenic Space Center (HSC). In this white paper, we summarize the outcome of the workshop, the most important aspect of it being the inclusion of $15$ Greek researchers to the LISA Consortium, raising our total number to $22$. At the same time, we present a road-map with the future steps and actions of the Greek Gravitational Wave community with respect to the future LISA mission.

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N. Karnesis, N. Stergioulas, G. Pappas, et. al.
Mon, 12 Sep 22
23/54

Comments: 11 pages, 3 figures

Gravitational Lensing in a Universe with matter and Cosmological Constant [CEA]

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http://arxiv.org/abs/2209.04063


We extend the results obtained in \cite{Piattella_2016, mcvittie_2015} for gravitational lensing in the McVittie metric by including the effect of the transition from the matter-dominated epoch of the Universe to the $\Lambda$-dominated era. We derive a formula that agrees with the previous results for the McVittie metric at lowest order, and compare the lensing angle predictions obtained from the Schwarzschild approximation, the McVittie model and higher order corrections to the McVittie model. In doing this, we test if, beyond the correction from the accelerated expansion of the Universe, there is a need for including the matter content of the Universe in modeling lens systems at the redshifts observerd in lens systems. We investigate if there is a need for a modification of the lens equation from these corrections, and if so, to which order and whether it is measurable. We find that while the effect is of the same order as the one calculated previously, there is no significant contribution to the bending angle, as the 1st order effect is already of order $\mathcal{O}(\theta_O^4)$ in the observed angle.

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P. Bessa and O. Piattella
Mon, 12 Sep 22
25/54

Comments: 6 pages, 3 figures

Accumulation of elastic strain toward crustal fracture in magnetized neutron stars [HEAP]

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http://arxiv.org/abs/2209.04136


This study investigates elastic deformation driven by the Hall drift in a magnetized neutron-star crust. Although the dynamic equilibrium initially holds without elastic displacement, the magnetic-field evolution changes the Lorentz force over a secular timescale, which inevitably causes the elastic deformation to settle in a new force balance. Accordingly, elastic energy is accumulated, and the crust is eventually fractured beyond a particular threshold. We assume that the magnetic field is axially symmetric, and we explicitly calculate the breakup time, maximum elastic energy stored in the crust, and spatial shear-stress distribution. For the barotropic equilibrium of a poloidal dipole field expelled from the interior core without a toroidal field, the breakup time corresponds to a few years for the magnetars with a magnetic field strength of $\sim 10^{15}$G; however, it exceeds 1 Myr for normal radio pulsars. The elastic energy stored in the crust before the fracture ranges from $10^{41}$ to $10^{45}$ erg, depending on the spatial-energy distribution. Generally, a large amount of energy is deposited in a deep crust. The energy released at fracture is typically $\sim 10^{41}$ erg when the rearrangement of elastic displacements occurs only in the fragile shallow crust. The amount of energy is comparable to the outburst energy on the magnetars.

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Y. Kojima
Mon, 12 Sep 22
48/54

Comments: 14 pages, 5 figures

Inspirals from the innermost stable circular orbit of Kerr black holes: Exact solutions and universal radial flow [CL]

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http://arxiv.org/abs/2209.03579


We present exact solutions of test particle orbits spiralling inward from the innermost stable circular orbit (ISCO) of a Kerr black hole. Our results are valid for any allowed value of the angular momentum $a$-parameter of the Kerr metric. These solutions are of considerable physical interest. In particular, the radial 4-velocity of these orbits is both remarkably simple and, with the radial coordinate scaled by its ISCO value, universal in form, otherwise completely independent of the black hole spin.

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A. Mummery and S. Balbus
Fri, 9 Sep 22
7/76

Comments: Accepted for publication in Physical Review Letters. 5 pages 3 figures

Neutron stars as extreme laboratories for gravity tests [CL]

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http://arxiv.org/abs/2209.03351


Neutron stars are versatile in their application to studying various important aspects of fundamental physics, in particular strong-field gravity tests and the equation of state for super-dense nuclear matter at low temperatures. However, in many cases these two objectives are degenerate to each other. We discuss how pulsar timing and gravitational waves provide accurate measurements of neutron star systems and how to effectively break the degeneracy using tools like universal relations. We also present perspectives on future opportunities and challenges in the field of neutron star physics.

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L. Shao and K. Yagi
Fri, 9 Sep 22
9/76

Comments: 5 pages, 2 figures; accepted by Science Bulletin