Tag Archives: General Relativity and Quantum Cosmology

Shadow of regular black hole in scalar-tensor-vector gravity theory [CL]

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http://arxiv.org/abs/2211.15040


We investigate the shadow cast by a regular black hole in scalar-tensor-vector mOdified gravity theory. This black hole differs from a Schwarzschild-Kerr black hole by the dimensionless parameter $\beta$. The size of the shadow depends on this parameter. Increasing the value of the parameter $\beta$ shrinks the shadow. A critical value of the parameter $\beta$ is found to be $\beta_{\rm crit}=0.40263$. The shadow for the horizonless dark compact object has been analysed for the static, spherically symmetric case and compared with M87* and Sgr A* data. Shadow observables have been determined in the context of the regular black hole and used for obtaining the energy emission rate. The peak of the energy emission rate shifts to lower frequency for the increasing value of the parameter $\beta$.

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S. Sau and J. Moffat
Tue, 29 Nov 22
70/80

Comments: 29 pages, 13 figures

Primordial black holes from Higgs inflation with a Gauss-Bonnet coupling [CEA]

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http://arxiv.org/abs/2211.13364


Primordial black holes (PBHs) can be the source for all or a part of today’s dark matter density. Inflation provides a mechanism for generating the seeds of PBHs in the presence of a temporal period where the velocity of an inflaton field $\phi$ rapidly decreases toward 0. We compute the primordial power spectra of curvature perturbations generated during Gauss-Bonnet (GB) corrected Higgs inflation in which the inflaton field has not only a nonminimal coupling to gravity but also a GB coupling. For a scalar-GB coupling exhibiting a rapid change during inflation, we show that curvature perturbations are sufficiently enhanced by the appearance of an effective potential $V_{\rm eff}(\phi)$ containing the structures of plateau-type, bump-type, and their intermediate type. We find that there are parameter spaces in which PBHs can constitute all dark matter for these three types of $V_{\rm eff}(\phi)$. In particular, models with bump- and intermediate-types give rise to the primordial scalar and tensor power spectra consistent with the recent Planck data on scales relevant to the observations of cosmic microwave background. This property is attributed to the fact that the number of e-foldings $\Delta N_c$ acquired around the bump region of $V_{\rm eff}(\phi)$ can be as small as a few, in contrast to the plateau-type where $\Delta N_c$ typically exceeds the order of 10.

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R. Kawaguchi and S. Tsujikawa
Mon, 28 Nov 22
1/93

Comments: 20 pages, 7 figures

Machine learning cosmic inflation [CEA]

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http://arxiv.org/abs/2211.14142


We present a machine-learning approach, based on the genetic algorithms (GA), that can be used to reconstruct the inflationary potential directly from cosmological data. We create a pipeline consisting of the GA, a primordial code and a Boltzmann code used to calculate the theoretical predictions, and Cosmic Microwave Background (CMB) data. As a proof of concept, we apply our methodology to the Planck CMB data and explore the functional space of single-field inflationary potentials in a non-parametric, yet analytical way. We show that the algorithm easily improves upon the vanilla model of quadratic inflation and proposes slow-roll potentials better suited to the data, while we confirm the robustness of the Starobinsky inflation model (and other small-field models). Moreover, using unbinned CMB data, we perform a first concrete application of the GA by searching for oscillatory features in the potential in an agnostic way, and find very significant improvements upon the best featureless potentials, $\Delta \chi^2 < -20$. These encouraging preliminary results motivate the search for resonant features in the primordial power spectrum with a multimodal distribution of frequencies. We stress that our pipeline is modular and can easily be extended to other CMB data sets and inflationary scenarios, like multifield inflation or theories with higher-order derivatives.

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A. Kamerkar, S. Nesseris and L. Pinol
Mon, 28 Nov 22
10/93

Comments: 14 pages, 10 figures, 2 tables. Comments welcome

Maximum mass of relativistic self-gravitating Bose-Einstein condensates with repulsive or attractive $|\varphi|^4$ self-interaction [CL]

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http://arxiv.org/abs/2211.13237


We derive an approximate analytical expression of the maximum mass of relativistic self-gravitating Bose-Einstein condensates with repulsive or attractive $|\varphi|^4$ self-interaction. This expression interpolates between the general relativistic maximum mass of noninteracting bosons stars, the general relativistic maximum mass of bosons stars with a repulsive self-interaction in the Thomas-Fermi limit, and the Newtonian maximum mass of dilute axion stars with an attractive self-interaction [P.H. Chavanis, Phys. Rev. D {\bf 84}, 043531 (2011)]. We obtain the general structure of our formula from simple considerations and determine the numerical coefficients in order to recover the exact asymptotic expressions of the maximum mass in particular limits. As a result, our formula should provide a relevant approximation of the maximum mass of relativistic boson stars for any value (positive and negative) of the self-interaction parameter. We discuss the evolution of the system above the maximum mass and consider application of our results to dark matter halos and inflaton clusters. We also make a short review of boson stars and Bose-Einstein condensate dark matter halos, and point out analogies with models of extended elementary particles.

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P. Chavanis
Mon, 28 Nov 22
18/93

Comments: arXiv admin note: text overlap with arXiv:gr-qc/9801063 by other authors

Logarithmic Duality of the Curvature Perturbation [CEA]

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http://arxiv.org/abs/2211.13932


We study the comoving curvature perturbation $\mathcal{R}$ in general single-field inflation models whose potential can be approximated by a piecewise quadratic potential $V(\varphi)$ by using the $\delta N$ formalism. We find a general formula for $\mathcal{R}(\delta\varphi)$, which consists of a sum of logarithmic functions of the field perturbation $\delta\varphi$ at the point of interest, as well as of its field velocity perturbations $\delta\pi_*$ at the boundaries of each quadratic piece, which are functions of $\delta\varphi$ through the equations of motion. In some simple cases, $\mathcal{R}(\delta\varphi)$ reduces to a single logarithm, which yields either the renowned “exponential tail” of the probability distribution function of $\mathcal{R}$ or the Gumbel distribution.

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S. Pi and M. Sasaki
Mon, 28 Nov 22
25/93

Comments: 7 pages, 3 figures

Aberration of gravitational waveforms by peculiar velocity [CL]

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http://arxiv.org/abs/2211.14183


One key prediction of General Relativity is that gravitational waves are emitted with a pure spin-2 polarisation. Any extra polarisation mode, spin-1 or spin-0, is consequently considered a smoking gun for deviations from General Relativity. In this paper, we show that the velocity of merging binaries with respect to the observer gives rise to spin-1 polarisation in the observer frame even in the context of General Relativity. These are pure projection effects, proportional to the plus and cross polarisations in the source frame, hence they do not correspond to new degrees of freedom. We demonstrate that the spin-1 modes can always be rewritten as pure spin-2 modes coming from an aberrated direction. Since gravitational waves are not isotropically emitted around binary systems, this aberration modifies the apparent orientation of the binary system with respect to the observer: the system appears slightly rotated due to the source velocity. Fortunately, this bias does not propagate to other parameters of the system (and therefore does not spoil tests of General Relativity), since the impact of the velocity can be fully reabsorbed into new orientation angles.

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C. Bonvin, G. Cusin, C. Pitrou, et. al.
Mon, 28 Nov 22
28/93

Comments: 13 pages, 4 figures

Prospects of Probing Dark Matter Condensates with Gravitational Waves [CL]

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http://arxiv.org/abs/2211.13988


The Lambda-Cold Dark Matter model explains cosmological observations most accurately till date. However, it is still plagued with various shortcomings at galactic scales. Models of dark matter such as superfluid dark matter, Bose-Einstein Condensate(BEC) dark matter and fuzzy dark matter have been proposed to overcome some of these drawbacks. In this work, we probe these models using the current constraint on the gravitational wave (GW) propagation speed coming from the binary neutron star GW170817 detection by LIGO-Virgo detector network and use it to study the allowed parameter space for these three models for Advanced LIGO, LISA, IPTA and SKA detection frequencies. The speed of GW has been shown to depend upon the refractive index of the medium, which in turn, depends on the dark matter model parameters through the density profile of the galactic halo. We constrain the parameter space for these models using the bounds coming from GW speed measurement and the Milky Way radius bound. Our findings suggest that with Advanced LIGO-Virgo detector sensitivity, the three models considered here remain unconstrained. A meaningful constraint can only be obtained for detection frequencies $\leq 10^{-9}$ Hz, which falls in the detection range of radio telescopes such as IPTA and SKA. Considering this best possible case, we find that out of the three condensate models, the fuzzy dark matter model is the most feasible scenario to be falsified/ validated in near future.

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S. Banerjee, S. Bera and D. Mota
Mon, 28 Nov 22
36/93

Comments: 25 pages, 6 figures

A hybrid model for the dark sector [CL]

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http://arxiv.org/abs/2211.13653


Diverse cosmological and astrophysical observations strongly hint at the presence of dark matter and dark energy in the Universe. One of the main goals of Cosmology is to explain the nature of these two components. It may well be that both dark matter and dark energy have a common origin. In this paper, we develop a model in which the dark sector arises due to an interplay between two interacting scalar fields. Employing a hybrid inflation potential, we show that the model can be described as a system of a pressureless fluid coupled to a light scalar field. We discuss this setup’s cosmological consequences and the observational signatures in the cosmic microwave background radiation and the large-scale structures.

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C. Bruck, G. Poulot and E. Teixeira
Mon, 28 Nov 22
40/93

Comments: 13 pages, 10 figures

Compact Binaries through a Lens: Silent vs. Detectable Microlensing for the LIGO-Virgo-KAGRA Gravitational Wave Observatories [CL]

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http://arxiv.org/abs/2211.13604


Massive objects located between Earth and a compact binary merger can act as a magnifying glass improving the sensitivity of gravitational wave detectors to distant events. A point mass lens between the detector and the source can manifest itself either through an amplification of the gravitational wave signal in a frequency dependent manner that is maximum at merger or through magnification combined with the appearance of a second image that interferes with the first creating a regular, predictable pattern. We map the increase in the signal to noise ratio for upcoming LVK observations as a function of the mass of the lens $M_L$ and dimensionless source position y for any point mass lens between the detector and the binary source. We find that most microlensing is silent with mismatch under $10\%$ and may never be identified as lensed. To quantify detectability, we compute the optimal match between the lensed waveform and the waveforms in the unlensed template bank and provide a map of the match. The higher the mismatch with unlensed templates, the more detectable lensing is. Furthermore, we estimate the probability of lensing, and find that the redshift to which binary mergers are visible with the LVK increases from $z \approx 1$ to $z\approx 3.2$ for a total detected mass $M_{det} = 120 M_\odot$. The overall probability of lensing is $<20\%$ of all detectable events above the threshold SNR for $M_{det} = 120 M_\odot$ and $<5\%$ for more common events with $M_{det} = 60 M_\odot$. We find that there is a selection bias for detectable lensing that favors events that are close to the line of sight $y \lesssim 0.5$. Black hole binary searches could thus improve their sensitivity by introducing a prior that takes the bias into account.

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R. Bondarescu, H. Ubach, O. Bulashenko, et. al.
Mon, 28 Nov 22
43/93

Comments: 17 pages, 12 Figures, Submitted to Phys. Rev. D

Hybrid $α$-attractors, primordial black holes and gravitational wave backgrounds [CEA]

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http://arxiv.org/abs/2211.14262


We investigate the two-stage inflation regime in the theory of hybrid cosmological $\alpha$-attractors. The spectrum of inflationary perturbations is compatible with the latest Planck/BICEP/Keck results, thanks to the attractor properties of the model. However, at smaller scales, it may have a very high peak of controllable width and position, leading to a copious production of primordial black holes (PBH) and generation of a stochastic background of gravitational waves (SGWB).

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M. Braglia, A. Linde, R. Kallosh, et. al.
Mon, 28 Nov 22
52/93

Comments: 39 pages, 12 figures

Slow-roll inflation in $f\left(R, T, R_{ab}T^{ab}\right)$ gravity [CL]

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http://arxiv.org/abs/2211.13233


In the framework of $f\left(R, T, R_{ab}T^{ab}\right)$ gravity theory, the slow-roll approximation of the cosmic inflation is investigated, where $T$ is the trace of the energy-momentum tensor $T^{ab}$, $R$ and $R_{ab}$ are the Ricci scalar and tensor, respectively. After obtaining the equations of motion of the gravitational field from the action principle in the spatially flat FLRW metric, the fundamental equations of this theory are received by introducing the inflation scalar field as the matter and taking into account only the minimum curvature-inflation coupling term. Remarkably, after taking the slow-roll approximation, the identical equations as in $f(R, T)$ gravity with a $RT$ mixing term are derived. Several potentials of interest in different domains are evaluated individually, calculating the slow-roll parameter and the e-folding number $N$. Finally, we analyze the behavior of the inflation scalar field under perturbation while ignoring the effect of metric perturbations. This research complements the slow-roll inflation in the modified theory of gravity.

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Z. Feng
Mon, 28 Nov 22
53/93

Comments: 14 pages, 1 figure

Skewness consistency relation in large-scale structure and test of gravity theory [CEA]

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http://arxiv.org/abs/2211.13453


We investigate the skewness of galaxy number density fluctuations as a possible probe to test gravity theories. We find that the specific linear combination of the skewness parameters corresponds to the coefficients of the second-order kernels of the density contrast, which can be regarded as the consistency relation and used as a test of general relativity and modified gravity theories. We also extend the analysis of the skewness parameters from real space to redshift space and derive the redshift-space skewness consistency relation.

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D. Yamauchi, S. Ishimaru, T. Matsubara, et. al.
Mon, 28 Nov 22
58/93

Comments: 18 pages, 2 figures

Chasing Super-Massive Black Hole merging events with $Athena$ and LISA [HEAP]

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http://arxiv.org/abs/2211.13759


The European Space Agency is studying two large-class missions bound to operate in the $2030$s, and aiming at investigating the most energetic phenomena in the Universe. $Athena$ is poised to study the physical conditions of baryons in large-scale structures, as well as to yield a census of accreting super-massive black holes down to the epoch of reionization; the Laser Interferometer Space Antenna (LISA) will extend the hunt for Gravitational Wave (GW) events to the mHz regime. While the science cases of the two missions are independently outstanding, we discuss in this paper the $additional$ science that their concurrent operation could yield. We focus on the multi-messenger study of Super-Massive (M$\lesssim 10^7\rm M_{\odot}$) Black Hole Mergers (SMBHMs), accessible to $Athena$ up to $z\sim2$. The simultaneous measurement of their electro-magnetic (EM) and GW signals may enable unique experiments in the domains of astrophysics, fundamental physics, and cosmography. Key to achieve these results will be the LISA capability of locating a SMBHM event with an error box comparable to, or better than the field-of-view of the $Athena$ Wide Field Imager ($\simeq0.4$deg$^2$). LISA will achieve such an accuracy several hours prior to merging for the highest signal-to-noise events. While theoretical predictions of the EM emission are still uncertain, this opens in principle the possibility of truly concurrent EM and GW studies of the merger phase. LISA localization improves significantly at merging, and is likely to reach the arcminute-level for a sizeable fraction of events at $z\lesssim 0.5$ and masses $\lesssim10^6\rm M_{\odot}$, well within the detection capability of $Athena$. We also briefly discuss the prospective of $Athena$ studies for other classes of GW-emitting black hole binaries, for which theoretical predictions are admittedly extremely uncertain. [abridged]

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L. Piro, M. Colpi, J. Aird, et. al.
Mon, 28 Nov 22
59/93

Comments: 18 pages, 8 figures. Submitted to MNRAS

Crustal magnetic fields do not lead to magnetar-strength amplifications in binary neutron-star mergers [HEAP]

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http://arxiv.org/abs/2211.13661


The amplification of magnetic fields plays an important role in explaining numerous astrophysical phenomena associated with binary neutron-star mergers, such as mass ejection and the powering of short gamma-ray bursts. Magnetic fields in isolated neutron stars are often assumed to be confined to a small region near the stellar surface, while they are normally taken to fill the whole stars in the numerical modelling. By performing high-resolution, global, and high-order general-relativistic magnetohydrodynamic simulations we investigate the impact of a purely crustal magnetic field and contrast it with the standard configuration consisting of a dipolar magnetic field with the same magnetic energy but filling the whole star. While the crust-configurations are very effective in generating strong magnetic fields during the Kelvin-Helmholtz-instability stage, they fail to achieve the same level of magnetic-field amplification of the full-star configurations. This is due to the lack of magnetized material in the neutron-star interiors to be used for further turbulent amplification and to the surface losses of highly magnetized matter in the crust-configurations. Hence, the final magnetic energies in the two configurations differ by more than one order of magnitude. We briefly discuss the impact of these results on astrophysical observables and how they can be employed to deduce the magnetic topology in merging binaries.

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M. Chabanov, S. Tootle and L. Rezzolla
Mon, 28 Nov 22
65/93

Comments: 10 pages, 5 figures, videos of the simulations available on this https URL

Gravitational waves radiated by magnetic galactic binaries and detection by LISA [CL]

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http://arxiv.org/abs/2211.14278


In the context of the future Laser Interferometer Space Antenna (LISA) mission, galactic binary systems of white dwarfs and neutron stars will represent the dominant source of Gravitational Waves (GWs) within the $10^{-4}-10^{-1}\,\mathrm{Hz}$ frequency band. It is expected that LISA will measure simultaneously, the GWs from more than ten thousands of these compact galactic binaries. The analysis of such a superposition of signals will represent one of the greatest challenge for the mission. Currently, in the LISA Datacode Challenge, each galactic binary is modeled as a quasi-monochromatic source of GWs. This corresponds to the circular motion of two point-masses at the 2.5 post-Newtonian approximation. If this picture is expected to be an accurate description for most of the galactic binaries that LSIA will detect, we nevertheless expect to observe eccentric systems with complex physical properties beyond the point-mass approximation. In this work, we investigate how a binary system of highly magnetic objects in quasi-circular orbit could affect the quasi-monochromatic picture of the GW signal detected by LISA. We demonstrate that the eccentricity generates additional frequency peaks at harmonics of the mean motion and that magnetism is responsible for shifting each frequency peak with respect to the case without magnetism. We provide analytical estimates and argue that LISA will be able to detect magnetism if it can measure the main peaks at two and three times the mean motion with a sufficient accuracy.

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A. Bourgoin, C. Poncin-Lafitte, S. Mathis, et. al.
Mon, 28 Nov 22
76/93

Comments: 4 pages, 1 figure, proceedings Les rencontres de Moriond

Resonant friction on discs in galactic nuclei [GA]

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http://arxiv.org/abs/2211.12754


We argue that resonant friction has a dramatic effect on a disc whose rotation direction is misaligned with that of its host nuclear star cluster. The disc’s gravity causes gravitational perturbation of the cluster that in turn exerts a strong torque back onto the disc. We argue that this torque may be responsible for the observed disruption of the clockwise disc of young stars in the Galactic Center, and show in numerical experiments that it produces the observed features in the distribution of the stars’ angular momenta. More generally, we speculate that the rotation of nuclear star clusters has a stabilizing effect on the orientation of transient massive accretion discs around the supermassive black holes residing in their centers, and thus on the directions and magnitudes of the black-hole spins.

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Y. Levin
Thu, 24 Nov 22
2/71

Comments: submitted to ApJ

Constraints on Yukawa gravity parameters from observations of bright stars [GA]

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http://arxiv.org/abs/2211.12951


In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction $\Lambda$ and universal constant $\delta$) with the Schwarzschild precession of the S-stars assuming that the observed Schwarzschild precession will be equal to their GR estimates. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant $\delta$, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction $\delta$ and find that this parameter has strong influence on range of Yukawa interaction $\Lambda$. Using MCMC simulations we obtain the best-fit values and uncertanties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories.

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P. Jovanović, V. Jovanović, D. Borka, et. al.
Thu, 24 Nov 22
15/71

Comments: 22 pages, 1 table, 5 figures

One-loop tensor power spectrum from an excited scalar field during inflation [CEA]

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http://arxiv.org/abs/2211.12766


We present a consistent one-loop calculation for the inflationary tensor power spectrum in the presence of an excited spectator scalar field using the in-in formalism. We find that the super-horizon primordial power spectrum of the tensor mode can be scale-invariantly enhanced or reduced by the loop effects of a subhorizon scalar field. Our calculation also includes the scalar-induced gravitational wave spectrum classically computed in the previous literature, which is significant only near the scales where the scalar field is amplified. The super-horizon enhancement is a higher-order effect of the interaction Hamiltonian, which can be understood as a Bogoliubov transformation introduced by nonlinear interactions. On the other hand, the scale-invariant reduction of the tensor power spectrum may occur due to the fourth-order scalar-scalar-tensor-tensor coupling. This phenomenon can be understood as the evolution of an anisotropic Bianchi type-I background in the separate universe approach. Our result suggests that large-scale measurements may indirectly test the dramatic effects of small-scale cosmological perturbations through loop corrections. This possibility opens a new ground in probing the small-scale physics of the primordial Universe through gravitational wave detectors of cosmological scales.

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A. Ota, M. Sasaki and Y. Wang
Thu, 24 Nov 22
28/71

Comments: 22 pages, 5 figures, full details of 2209.02272 and more

Searching for double-peak and doubly-broken gravitational-wave spectra from Advanced LIGO-Virgo's first three observing runs [CL]

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http://arxiv.org/abs/2211.13111


The current LIGO-Virgo observing run has been pushing the sensitivity limit to touch the stochastic gravitational-wave backgrounds (SGWBs). However, no significant detection has been reported to date for any single dominated source of SGWBs with a single broken-power-law (BPL) spectrum. Nevertheless, it could equally well escape from existing Bayesian searches from, for example, two comparable dominated sources with two separate BPL spectra (double-peak case) or a single source with a doubly-BPL (DBPL) spectrum (doubly-broken case). In this paper, we put constraints on these two cases from Advanced LIGO-Virgo’s first three observing runs. We found strong negative evidence for the double-peak case and hence place 95\% confidence-level (CL) upper limits $\Omega_\mathrm{BPL,1}<2.5\times10^{-7}$ and $\Omega_\mathrm{BPL,2}<9.4\times10^{-8}$ on the two BPL spectra amplitudes with respect to the unresolved compact-binary-coalescence (CBC) amplitude $\Omega_\mathrm{CBC}<5.6\times10^{-9}$. We further found weak negative evidence for the doubly-broken case and hence place 95\% CL upper limit $\Omega_\mathrm{DBPL}<1.7\times10^{-7}$ on the overall amplitude of the DBPL spectrum with respect to $\Omega_\mathrm{CBC}<6.0\times10^{-9}$. The implications of cosmological first-order phase transitions are also discussed.

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W. Yu and S. Wang
Thu, 24 Nov 22
48/71

Comments: 5 pages + references, 5 figures, 1 table

Gravitational radiation from binary systems in $f(R)$ gravity: A semi-classical approach [CL]

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http://arxiv.org/abs/2211.12947


The rate of energy loss and orbital period decay of quasi-stable compact binary systems are derived in $f(R)$ theory of gravity using the method of a single vertex graviton emission process from a classical source. After linearising the $f(R)$ action written in an equivalent scalar-tensor format in the Einstein frame, we identify the appropriate interaction terms between the massless spin-2 tensor mode, massive scalar mode, and the energy momentum tensor. The definition of the scalar field is related to the $f(R)$ models. Then using the interaction vertex we compute the rate of energy loss due to spin-2 quadrupole radiation, which comes out to be the same as the Peter-Mathews formula with a multiplication factor, and also the energy loss due to the scalar dipole radiation. The total energy loss is the sum of these two contributions. Our derivation is most general as it is applicable for both arbitrary eccentricity of the binary orbits and arbitrary mass of the scalar field. Using the derived theoretical formula for the period decay of the binary systems, we compare the predictions of $f(R)$ gravity and general relativity for the observations of three binary systems, i.e. Hulse-Taylor Binary, PSR J1141-6545 and PSR J1738+0333. Thus we put bound on three well-known $f(R)$ dark energy models, namely the Hu-Sawicki, the Straobinsky, and the Tsujukawa model. We get the best constraint on $f'(R_0)-1$ (where $R_0$ is the scalar curvature of the Universe at the present epoch) from the Tsujikawa model, i.e $\vert f'(R_0)-1\vert < 3.44\times 10^{-4}$. This bound is stronger than those from most of the astrophysical observations and even some cosmological observations.

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A. Narang, S. Mohanty and S. Jana
Thu, 24 Nov 22
67/71

Comments: 21 pages, 1 figure, 2 tables

One-loop tensor power spectrum from an excited scalar field during inflation [CEA]

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http://arxiv.org/abs/2211.12766


We present a consistent one-loop calculation for the inflationary tensor power spectrum in the presence of an excited spectator scalar field using the in-in formalism. We find that the super-horizon primordial power spectrum of the tensor mode can be scale-invariantly enhanced or reduced by the loop effects of a subhorizon scalar field. Our calculation also includes the scalar-induced gravitational wave spectrum classically computed in the previous literature, which is significant only near the scales where the scalar field is amplified. The super-horizon enhancement is a higher-order effect of the interaction Hamiltonian, which can be understood as a Bogoliubov transformation introduced by nonlinear interactions. On the other hand, the scale-invariant reduction of the tensor power spectrum may occur due to the fourth-order scalar-scalar-tensor-tensor coupling. This phenomenon can be understood as the evolution of an anisotropic Bianchi type-I background in the separate universe approach. Our result suggests that large-scale measurements may indirectly test the dramatic effects of small-scale cosmological perturbations through loop corrections. This possibility opens a new ground in probing the small-scale physics of the primordial Universe through gravitational wave detectors of cosmological scales.

Read this paper on arXiv…

A. Ota, M. Sasaki and Y. Wang
Thu, 24 Nov 22
10/71

Comments: 22 pages, 5 figures, full details of 2209.02272 and more

Resonant friction on discs in galactic nuclei [GA]

Posted on by

http://arxiv.org/abs/2211.12754


We argue that resonant friction has a dramatic effect on a disc whose rotation direction is misaligned with that of its host nuclear star cluster. The disc’s gravity causes gravitational perturbation of the cluster that in turn exerts a strong torque back onto the disc. We argue that this torque may be responsible for the observed disruption of the clockwise disc of young stars in the Galactic Center, and show in numerical experiments that it produces the observed features in the distribution of the stars’ angular momenta. More generally, we speculate that the rotation of nuclear star clusters has a stabilizing effect on the orientation of transient massive accretion discs around the supermassive black holes residing in their centers, and thus on the directions and magnitudes of the black-hole spins.

Read this paper on arXiv…

Y. Levin
Thu, 24 Nov 22
15/71

Comments: submitted to ApJ

Searching for double-peak and doubly-broken gravitational-wave spectra from Advanced LIGO-Virgo's first three observing runs [CL]

Posted on by

http://arxiv.org/abs/2211.13111


The current LIGO-Virgo observing run has been pushing the sensitivity limit to touch the stochastic gravitational-wave backgrounds (SGWBs). However, no significant detection has been reported to date for any single dominated source of SGWBs with a single broken-power-law (BPL) spectrum. Nevertheless, it could equally well escape from existing Bayesian searches from, for example, two comparable dominated sources with two separate BPL spectra (double-peak case) or a single source with a doubly-BPL (DBPL) spectrum (doubly-broken case). In this paper, we put constraints on these two cases from Advanced LIGO-Virgo’s first three observing runs. We found strong negative evidence for the double-peak case and hence place 95\% confidence-level (CL) upper limits $\Omega_\mathrm{BPL,1}<2.5\times10^{-7}$ and $\Omega_\mathrm{BPL,2}<9.4\times10^{-8}$ on the two BPL spectra amplitudes with respect to the unresolved compact-binary-coalescence (CBC) amplitude $\Omega_\mathrm{CBC}<5.6\times10^{-9}$. We further found weak negative evidence for the doubly-broken case and hence place 95\% CL upper limit $\Omega_\mathrm{DBPL}<1.7\times10^{-7}$ on the overall amplitude of the DBPL spectrum with respect to $\Omega_\mathrm{CBC}<6.0\times10^{-9}$. The implications of cosmological first-order phase transitions are also discussed.

Read this paper on arXiv…

W. Yu and S. Wang
Thu, 24 Nov 22
49/71

Comments: 5 pages + references, 5 figures, 1 table

Constraints on Yukawa gravity parameters from observations of bright stars [GA]

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http://arxiv.org/abs/2211.12951


In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction $\Lambda$ and universal constant $\delta$) with the Schwarzschild precession of the S-stars assuming that the observed Schwarzschild precession will be equal to their GR estimates. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant $\delta$, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction $\delta$ and find that this parameter has strong influence on range of Yukawa interaction $\Lambda$. Using MCMC simulations we obtain the best-fit values and uncertanties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories.

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P. Jovanović, V. Jovanović, D. Borka, et. al.
Thu, 24 Nov 22
57/71

Comments: 22 pages, 1 table, 5 figures

Gravitational radiation from binary systems in $f(R)$ gravity: A semi-classical approach [CL]

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http://arxiv.org/abs/2211.12947


The rate of energy loss and orbital period decay of quasi-stable compact binary systems are derived in $f(R)$ theory of gravity using the method of a single vertex graviton emission process from a classical source. After linearising the $f(R)$ action written in an equivalent scalar-tensor format in the Einstein frame, we identify the appropriate interaction terms between the massless spin-2 tensor mode, massive scalar mode, and the energy momentum tensor. The definition of the scalar field is related to the $f(R)$ models. Then using the interaction vertex we compute the rate of energy loss due to spin-2 quadrupole radiation, which comes out to be the same as the Peter-Mathews formula with a multiplication factor, and also the energy loss due to the scalar dipole radiation. The total energy loss is the sum of these two contributions. Our derivation is most general as it is applicable for both arbitrary eccentricity of the binary orbits and arbitrary mass of the scalar field. Using the derived theoretical formula for the period decay of the binary systems, we compare the predictions of $f(R)$ gravity and general relativity for the observations of three binary systems, i.e. Hulse-Taylor Binary, PSR J1141-6545 and PSR J1738+0333. Thus we put bound on three well-known $f(R)$ dark energy models, namely the Hu-Sawicki, the Straobinsky, and the Tsujukawa model. We get the best constraint on $f'(R_0)-1$ (where $R_0$ is the scalar curvature of the Universe at the present epoch) from the Tsujikawa model, i.e $\vert f'(R_0)-1\vert < 3.44\times 10^{-4}$. This bound is stronger than those from most of the astrophysical observations and even some cosmological observations.

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A. Narang, S. Mohanty and S. Jana
Thu, 24 Nov 22
60/71

Comments: 21 pages, 1 figure, 2 tables

Formation, Possible Detection and Consequences of Highly Magnetized Compact Stars [HEAP]

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http://arxiv.org/abs/2211.11998


Over the past several years, there has been enormous interest in massive neutron stars and white dwarfs due to either their direct or indirect evidence. The recent detection of gravitational wave event GW190814 has confirmed the existence of compact stars with masses as high as $\sim2.5-2.67M_{\odot}$ within the so-called mass gap, indicating the existence of highly massive neutron stars. One of the primary goals to invoke massive compact objects was to explain the recent detections of over a dozen Type Ia supernovae, whose peculiarity lies with their unusual light curve, in particular the high luminosity and low ejecta velocity. In a series of recent papers, our group has proposed that highly magnetised white dwarfs with super-Chandrasekhar masses can be promising candidates for the progenitors of these peculiar supernovae. The mass-radius relations of these magnetised stars are significantly different from those of their non-magnetised counterparts, which leads to a revised super-Chandrasekhar mass-limit. These compact stars have wider ranging implications, including those for soft gamma-ray repeaters, anomalous X-ray pulsars, white dwarf pulsars and gravitational radiation. Here we review the development of the subject over the last decade or so, describing the overall state of the art of the subject as it stands now. We mainly touch upon the possible formation channels of these intriguing stars as well as the effectiveness of direct detection methods. These magnetised stars can have many interesting consequences, including reconsideration of them as possible standard candles.

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B. Mukhopadhyay and M. Bhattacharya
Wed, 23 Nov 22
24/71

Comments: 24 pages, 11 figures (23 pdf figures), 1 table; based on the invited (online) talk given by Banibrata Mukhopadhyay in “The Modern Physics of Compact Stars and Relativistic Gravity 2021” meeting held during September 27 – 30, 2021 at Yerevan, Armenia; invited review published in a special issue of Particles, edited by Armen Sedrakian; both authors have contributed equally to this work. arXiv admin note: text overlap with arXiv:2110.15374

Dark matter production via a non-minimal coupling to gravity [CL]

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http://arxiv.org/abs/2211.11773


We study postinflationary scalar dark matter production via its non-minimal coupling to gravity. During the inflaton oscillation epoch, dark matter is produced resonantly for a sufficiently large non-minimal coupling $\xi\gtrsim 5$. We find that backreaction on the curvature and rescattering effects typically become important for the values of $\xi$ above $30$, which invalidate simple estimates of the production efficiency. At large couplings, the dark matter yield becomes almost independent of $\xi$, signifying approximate quasi-equilibrium in the inflaton-dark matter system. Although the analysis gets complicated by the presence of apparent negative energy in the Jordan frame, this behaviour can be regularized by introducing mild dark matter self-interaction. Using lattice simulations, we delineate parameter space leading to the correct dark matter relic abundance.

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O. Lebedev, T. Solomko and J. Yoon
Wed, 23 Nov 22
34/71

Comments: 18 pages, 7 figures

Hybrid stars may have an inverted structure [CL]

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http://arxiv.org/abs/2211.12043


We propose a new stellar structure of compact stars, the “Cross stars” (CrSs) that consist of a hadronic matter core and a quark matter crust, with an inverted structure compared to the conventional hybrid stars. This distinct stellar structure naturally arises from the quark matter to hadronic matter transition associated with the chemical potential crossing, in the context of the quark matter hypothesis that either strange or up-down quark matter is the ground state of baryonic matter at low pressure. We find that the interplay between the hadronic matter and quark matter compositions of CrSs can help to reconcile the small radii constraints indicated by the LIGO/Virgo GW170817 event, the large radii constraints set for massive compact stars by recent NICER X-ray observations, and the recent observation of the most-massive pulsar PSR J0952-0607. This leaves more space open for the equation of states of both hadronic matter and quark matter.

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J. Ren and C. Zhang
Wed, 23 Nov 22
40/71

Comments: 10 pages, 6 figures

Can General Relativity play a role in galactic dynamics? [CL]

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http://arxiv.org/abs/2211.11815


We use the gravitoelectromagnetic approach to the solutions of Einstein’s equations in the weak-field and slow-motion approximation to investigate the impact of General Relativity on galactic dynamics. In particular, we focus on a particular class of the solutions for the gravitomagnetic field, and show that, contrary to what is expected, they may introduce non negligible corrections to the Newtonian velocity profile. The origin and the interpretation of these corrections are discussed and explicit applications to some galactic models are provided. These are the homogeneous solutions (HS) for the gravitomagnetic field, i.e. solutions with vanishing matter currents.

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D. Astesiano and M. Ruggiero
Wed, 23 Nov 22
43/71

Comments: 7 pages, 2 figures, accepted for publication as a Letter in Physical Review D

Generic modification of gravity, late time acceleration and Hubble tension [CL]

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http://arxiv.org/abs/2211.12041


We consider a scenario of large-scale modification of gravity that does not invoke extra degrees of freedom but includes coupling between baryonic matter and dark matter in the Einstein frame. The total matter energy density follows the standard conservation, and evolution has the character of deceleration in this frame. The model exhibits interesting features in the Jordan frame realized by virtue of a disformal transformation where individual matter components adhere to standard conservation but gravity is modified. A generic parametrization of disformal transformation leaves thermal history intact. It gives rise to late time acceleration in the Jordan frame, which necessarily includes phantom crossing, which, in the standard framework, can be realized using at least two scalar fields. This scenario is embodied by two distinguishing features, namely, acceleration in the Jordan frame and deceleration in the Einstein frame, and the possibility of resolution of the Hubble tension thanks to the emergence of the phantom phase at late times.

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M. Gangopadhyay, S. Pacif, M. Sami, et. al.
Wed, 23 Nov 22
50/71

Comments: N/A

Cosmography using strongly lensed gravitational waves from binary black holes [CEA]

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http://arxiv.org/abs/2211.12212


Third generation gravitational wave (GW) detectors are expected to detect millions of binary black hole (BBH) mergers during their operation period. A small fraction of them ($\sim 1\%$) will be strongly lensed by intervening galaxies and clusters, producing multiple observable copies of the GW signals. The expected number of lensed events and the distribution of the time delay between lensed events depend on the cosmology. We develop a Bayesian analysis method for estimating cosmological parameters from the detected number of lensed events and their time delay distribution. The expected constraints are comparable to that obtained from other cosmological measurements, but probing a different redshift regime ($z \sim 10$) that is not explored by other probes.

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S. Jana, S. Kapadia, T. Venumadhav, et. al.
Wed, 23 Nov 22
51/71

Comments: 9 pages, 7 figures (including supplementary material)

Second order scalar perturbations induced by primordial curvature and tensor perturbations [CEA]

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http://arxiv.org/abs/2211.11948


The primordial perturbations will inevitably generate higher order perturbations. We study the second order scalar perturbations generated by the primordial curvature and tensor perturbations in the radiation-dominated era. After presenting all the possible second-order source terms, we obtain the explicit expressions of the kernel functions and the power spectra of the second order scalar perturbations. The contributions from the initial second-order perturbations are considered. We calculate the power spectra of second order scalar perturbations for different tensor-to-scalar ratio $r$.

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Z. Changa, K. Tinga, X. Zhang, et. al.
Wed, 23 Nov 22
58/71

Comments: N/A

Non-perturbative massless minimal quantum scalar field with $V(φ)=λφ^4/4!+βφ^3/3!$ in the inflationary de Sitter spacetime [CL]

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http://arxiv.org/abs/2211.12027


We consider a massless, minimally coupled quantum scalar field theory with an asymmetric self interaction, $V (\phi) = \lambda\phi^4/4!+\beta\phi^3/3!$ ($\lambda >0$) in the inflationary de Sitter spacetime. This potential is bounded from below. While the $\beta=0$ case has been much well studied, the motivation behind taking such a hybrid potential corresponds to the fact that it might generate finite negative vacuum expectation values of $V(\phi)$ as well of $\phi$, leading to some dynamical screening of the inflationary cosmological constant, $\Lambda$, at late times, with the initial conditions, $\langle \phi \rangle=0=\langle V(\phi) \rangle $. In this work we first compute the vacuum expectation values of $\phi,\, \phi^2$ and $V(\phi)$, using the late time, non-perturbative stochastic formalism. The backreactions to the inflationary $\Lambda$ are estimated. We also compute the dynamically generated mass of the scalar field using $\langle \phi^2 \rangle$. We next compute $\langle\phi^2\rangle$ using quantum field theory with respect to the initial Bunch-Davies vacuum at one and two loop, using the Schwinger-Keldysh formalism. These results show non-perturbative secular logarithms, growing with the cosmological time. Using next a recently proposed renormalisation group inspired formalism, we attempt to find out a resummed $\langle\phi^2\rangle$. We have been able to resum some part of the same which contains contributions only from the local self energy. The corresponding dynamically generated mass is computed. Comparison of the stochastic and the quantum field theory results shows that they differ numerically, although they have similar qualitative behaviour. Possible reasons for such quantitative mismatch is discussed. The manifestation of strong non-classical effects in the results found via both the formalisms has been emphasised.

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S. Bhattacharya and N. Joshi
Wed, 23 Nov 22
61/71

Comments: v1, 35pp, 10 figures, 1 table

Are nonsingular black holes with super-Planckian hair ruled out by S2 star data? [CL]

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http://arxiv.org/abs/2211.11585


We propose a novel nonsingular black-hole spacetime representing a strong deformation of the Schwarzschild solution with mass $M$ by an additional hair $\ell$, which may be hierarchically larger than the Planck scale. Our black-hole model presents a de Sitter core and $\mathcal{O}(\ell^2/r^2)$ slow-decaying corrections to the Schwarzschild solution. Our black-hole solutions are thermodynamically preferred when $0.2 \lesssim \ell/GM \lesssim \, 0.3$ and are characterized by strong deviations in the orbits of test particles from the Schwarzschild case. In particular, we find corrections to the perihelion precession angle scaling linearly with $\ell$. We test our model using the available data for the orbits of the S2 star around $\text{SgrA}^*$. These data strongly constrain the value of the hair $\ell$, casting an upper bound on it of $\sim \, 0.47 \, GM$, but do not rule out the possible existence of regular black holes with super-Planckian hair.

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M. Cadoni, M. Laurentis, I. Martino, et. al.
Tue, 22 Nov 22
13/83

Comments: 6 pages, 2 figures, 1 table

IWDM: The fate of an interacting non-cold dark matter $-$ vacuum scenario [CEA]

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http://arxiv.org/abs/2211.11047


In almost every cosmological models, the equation of state of the dark matter is assumed to be zero (i.e. a pressure-less/cold dark matter). Although such hypothesis is motivated by the abundance of cold dark matter in the universe, there is however no compelling reason to set the dark matter equation of state to zero, rather, the more generic picture is to consider a free-to-vary dark matter equation of state and let the observational data decide its fate. With the growing sensitivity of the experimental data, we choose the second possibility and consider an interacting non-cold dark matter $-$ vacuum scenario in which the dark matter equation of state is constant but free-to-vary in an interval. Considering a very well known and most used interaction function in the literature, we constrain this scenario using the Cosmic Microwave Background (CMB) anisotropies and the CMB lensing reconstruction from the legacy Planck release, baryon acoustic oscillations distance measurements and the Pantheon catalogue from Supernovae Type Ia. We find that for all the observational data sets, a non-zero value of the dark matter equation of state is preferred at 68\% CL which indicates that a non-cold dark matter sector in the universe should be investigated further in order to understand the intrinsic nature of the dark matter sector.

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S. Pan, W. Yang, E. Valentino, et. al.
Tue, 22 Nov 22
40/83

Comments: 9 pages, 2 tables and 3 captioned figures

Minimal decoherence from inflation [CL]

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http://arxiv.org/abs/2211.11046


We compute the rate with which super-Hubble cosmological fluctuations are decohered during inflation, by their gravitational interactions with unobserved shorter-wavelength scalar and tensor modes. We do so using Open Effective Field Theory methods, that remain under control at the late times of observational interest, contrary to perturbative calculations. Our result is minimal in the sense that it only incorporates the self-interactions predicted by General Relativity in single-clock models (additional interaction channels should only speed up decoherence). We find that decoherence is both suppressed by the first slow-roll parameter and by the energy density during inflation in Planckian units, but that it is enhanced by the volume comprised within the scale of interest, in Hubble units. This implies that, for the scales probed in the Cosmic Microwave Background, decoherence is effective as soon as inflation proceeds above $\sim 5\times 10^{9}$ GeV. Alternatively, if inflation proceeds at GUT scale decoherence is incomplete only for the scales crossing out the Hubble radius in the last ~ 13 e-folds, of inflation. We also compute how short-wavelength scalar modes decohere primordial tensor perturbations, finding a faster rate unsuppressed by slow-roll parameters. Identifying the parametric dependence of decoherence, and the rate at which it proceeds, helps suggest ways to look for quantum effects.

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C. Burgess, R. Holman, G. Kaplanek, et. al.
Tue, 22 Nov 22
51/83

Comments: 31 pages + appendices, 7 figures

Perspectives on the Dark Sector [CL]

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http://arxiv.org/abs/2211.11273


I present some new perspectives on Dark Matter, Dark Energy and the origin of structure in the Universe. First, I argue that in order to understand the two latter issues, one needs to go beyond a standard point particle effective field theory analysis. Next, I review recent work attempting to construct a unified dark sector model from Heterotic superstring theory. I finish by discussing a new research effort to obtain early Universe cosmology directly from a non-perturbative definition of superstring theory.

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R. Brandenberger
Tue, 22 Nov 22
53/83

Comments: Invited concluding talk, 33rd Rencontres de Blois

Sudden braking and turning in the single/multi-stream inflation: primordial black hole formation [CEA]

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http://arxiv.org/abs/2211.11387


We study a two-field inflation model with a Gaussian bump on the potential, also known as the multi-stream inflation, which can give rise to multiply inflationary trajectories with various interesting phenomena. With a shifted Gaussian bump, the multiply streams are approximately reduced to a single stream. We find that when inflaton rounds the Gaussian potential, its speed is easily slowed down, and thus the slow-roll parameter can be largely reduced. Consequently, the original decaying modes of comoving curvature perturbations during the slow-roll phase start growing, and lead to enhanced small-scale density perturbations which can produce amounts of primordial black holes (PBHs) and associated scalar-induced gravitational waves. In addition, inflaton also undergoes sudden turnings at the encounter of the Gaussian potential, which is insignificant to the overall curvature power spectrum since their durations are quite short. Our work gives a simple example of the extension of a bump-like potential for PBH formation in a single-field inflation to a two-field case, which can relax the fine-tuning of initial conditions to some extent.

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C. Fu and C. Chen
Tue, 22 Nov 22
54/83

Comments: 25 pages, 6 figures

Entanglement masquerading in the CMB [CL]

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http://arxiv.org/abs/2211.11079


The simplest single-field inflation models capture all the relevant contributions to the patterns in the Cosmic Microwave Background (CMB) observed today. A key assumption in these models is that the quantum inflationary fluctuations that source such patterns are generated by a particular quantum state — the Bunch-Davies (BD) state. While this is a well-motivated choice from a theoretical perspective, the question arises of whether current data can rule out other, also well motivated, choices of states. In particular, as we previously demonstrated in arXiv:2104.13410 [hep-th], entanglement is naturally and inevitably dynamically generated during inflation given the presence of a “rolling” spectator scalar field — and the resulting entangled state will yield a primordial power spectrum with potentially measurable deviations compared to the canonical BD result. For this work we developed a perturbative framework to allow a systematic exploration of constraints on (or detection of) entangled states with Planck CMB data using Monte Carlo techniques. We have found that most entangled states accessible with our framework are consistent with the data. One would have to expand the framework to allow a greater variety of entangled states in order to saturate the Planck constraints and more systematically explore any preferences the data may have among the different possibilities.

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A. Adil, A. Albrecht, R. Baunach, et. al.
Tue, 22 Nov 22
55/83

Comments: 37 pages, 12 figures, 3 appendices

Probing de Sitter from the horizon [CL]

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http://arxiv.org/abs/2211.11672


In a QFT on de Sitter background, one can study correlators between fields pushed to the future and past horizons of a comoving observer. This is a neat probe of the physics in the observer’s causal diamond (known as the static patch). We use this observable to give a generalization of the quasinormal spectrum in interacting theories, and to connect it to the spectral density that appears in the K\”all\’en-Lehmann expansion of dS correlators. We also introduce a finite-temperature effective field theory consisting of free bulk fields coupled to a boundary. In matching it to the low frequency expansion of correlators, we find positivity constraints on the EFT parameters following from unitarity.

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M. Mirbabayi and F. Riccardi
Tue, 22 Nov 22
57/83

Comments: 24 pages, 3 figures

Determination of the angular momentum of the Kerr black hole from equatorial geodesic motion [CL]

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http://arxiv.org/abs/2211.10464


We present a method to determine the angular momentum of a black hole, based on observations of the trajectories of the bodies in the Kerr space-time. We use the Hamilton equations to describe the dynamics of a particle and present results for equatorial trajectories, obtaining an algebraic equation for the magnitude of the black hole’s angular momentum. We tailor a numerical code to solve the dynamical equations and use it to generate synthetic data. We apply the method in some representative examples, obtaining the parameters of the trajectories as well as the black hole’s angular momentum in good agreement with the input data.

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L. Villegas, E. Ramirez-Codiz, V. Jaramillo, et. al.
Tue, 22 Nov 22
59/83

Comments: 18 pages

Effect of the $σ$-cut potential on the properties of neutron stars with or without a hyperonic core [CL]

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http://arxiv.org/abs/2211.10616


Motivated by the recent observation of high-mass pulsars ($M \simeq 2 M_{\odot}$), we employ the $\sigma$-cut potential on the equation of state (EOS) of high-density matter and the properties of neutron stars within the relativistic mean-field (RMF) model using TM1$^{*}$ parameter set. The $\sigma$-cut potential is known to reduce the contributions of the $\sigma$ field, resulting in a stiffer EOS at high densities and hence leading to larger neutron star masses without affecting the properties of nuclear matter at normal saturation density. We also analyzed the effect of the same on pure neutron matter and also on the neutron star matter with and without hyperonic core and compared it with the available theoretical, experimental, and observational data. The corresponding tidal deformability ($\Lambda_{1.4}$) is also calculated. With the choice of meson-hyperon coupling fixed to hypernuclear potentials, we obtain $\approx 10~\%$ increase in mass by employing the $\sigma$-cut potential for $f_{s} = 0.6$. Our results are in good agreement with various experimental constraints and observational data, particularly with the GW170817 data.

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N. Patra, B. Sharma, A. Reghunath, et. al.
Tue, 22 Nov 22
68/83

Comments: 7 Pages, 6 Figures and 1 Table (Accepted in Phys. Rev. C)

$F(R)$ gravity inflationary model with $(R+R_0)^{3/2}$ term [CL]

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http://arxiv.org/abs/2211.10988


The proposed inflationary model, which is a one-parametric generalization of the Starobinsky $R+R^2$ model, includes the $(R+3m^2\beta^2)^{3/2}$ term, where the parameter $m$ is the inflaton mass, defined in the same way as in the Starobinsky model, and $\beta$ is a dimensionless constant. Using the conformal transformation and the Einstein frame potential, we obtain the inflationary parameters of the model proposed. The value of the tensor-to-scalar ratio $r$ is bigger than in the Starobinsky model. The considered inflationary model produces a good fit to current observation data.

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E. Pozdeeva and S. Vernov
Tue, 22 Nov 22
69/83

Comments: 11 pages, 2 figures

How does dark matter affect compact star properties and high density constraints of strongly interacting matter [HEAP]

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http://arxiv.org/abs/2211.10510


We study the impact of asymmetric bosonic dark matter on neutron star properties, including possible changes of tidal deformability, maximum mass, radius, and matter distribution inside the star. The conditions at which dark matter particles tend to condensate in the star’s core or create an extended halo are presented. We show that dark matter condensed in a core leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, which we will perceive as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo increases those observable quantities. Thus, observational data on compact stars could be affected by accumulated dark matter and, consequently, constraints we put on strongly interacting matter at high densities. To confirm the presence of dark matter in the compact star’s interior, and to break the degeneracy between the effect of accumulated dark matter and strongly interacting matter properties at high densities, several astrophysical and GW tests are proposed.

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V. Sagun, E. Giangrandi, O. Ivanytskyi, et. al.
Tue, 22 Nov 22
72/83

Comments: 8 pages, 3 figures, Proceeding of the 15th Quark Confinement and the Hadron Spectrum Conference

Massively parallel simulations of binary black holes with Dendro-GR [CL]

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http://arxiv.org/abs/2211.11575


We present results from the new Dendro-GR code. These include simulations of binary black hole mergers for mass ratios up to q=16. Dendro-GR uses Wavelet Adaptive Multi-Resolution (WAMR) to generate an unstructured grid adapted to the spacetime geometry together with an octree based data structure. We demonstrate good scaling, improved convergence properties and efficient use of computational resources. We validate the code with comparisons to LazEv.

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M. Fernando, D. Neilsen, Y. Zlochower, et. al.
Tue, 22 Nov 22
73/83

Comments: N/A

General Effective Field Theory of Teleparallel Gravity [CL]

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http://arxiv.org/abs/2211.11420


We construct the Effective Field Theory (EFT) of the teleparallel equivalent of general relativity (TEGR). Firstly, we present the necessary field redefinitions of the scalar field and the tetrads. Then we provide all the terms at next-to-leading-order, containing the torsion tensor and its derivatives, and derivatives of the scalar field, accompanied by generic scalar-field-dependent couplings, where all operators are suppressed by a scale $\Lambda$. Removing all redundant terms using the field redefinitions we result to the EFT of TEGR, which includes significantly more terms comparing to the EFT of General Relativity. Finally, we present an application in a cosmological framework. Interestingly enough, although GR and TEGR are completely equivalent at the level of classical equations, we find that their corresponding EFTs possess minor but non-zero differences. Hence, we do verify that at higher energies the excitation and the features of the extra degrees of freedom are slightly different in the two theories, thus making them theoretically distinguishable. Nevertheless, we mention that these differences are suppressed by the heavy mass scale $\Lambda$ and thus it is not guaranteed that they could be measured in future experiments and observations.

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M. Mylova, J. Said and E. Saridakis
Tue, 22 Nov 22
78/83

Comments: 16 pages, comments are welcome

Black holes shielded by magnetic fields [HEAP]

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http://arxiv.org/abs/2211.11356


Black holes (BHs) formed by collapsing of magnetized progenitors, have magnetic fields penetrating the event horizon, and there are several possible scenarios. Bearing this in mind and considering a Schwarzschild BH of mass $M$ immersed in a uniform magnetic field $B$, we show that all three frequencies related to the equatorial circular orbit of a test particle become imaginary for the orbits of radii $r_B > 2/B$. It signifies that if a BH is surrounded by a magnetic field of order $B \sim M^{-1}$, a test particle could unable to continue its regular geodesic motion from/at $r > r_B$, hence the accretion disk could not be formed, and the motion of other stellar objects around the BH could be absent. As the BHs are generally detected by watching for their effects on nearby stars and gas, a magnetic field of order $B \sim M^{-1}$ could be able to shield a BH in such a way that it could remain undetectable. Motivated with this theoretical investigation and considering the sphere (of radius $r_f$) of magnetic influence around an astrophysical BH, we constrain $B$, above which a magnetized BH could remain undetectable. For example, $M=10^9M_{\odot}$ BH surrounded by $B > 10^6$ G and $M=10M_{\odot}$ BH surrounded by $B > 10^{14}$ G could remain undetectable for $r_f \sim 10^5M$. In other words, our result also explains why a detected SMBH has surprisingly weak magnetic field.

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C. Chakraborty
Tue, 22 Nov 22
80/83

Comments: 8 pages including 4 figures

Probing phase transition in neutron stars via the crust-core interfacial mode [HEAP]

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http://arxiv.org/abs/2211.11529


Gravitational waves emitted from the binary neutron star (BNS) systems can carry information about the dense matter phase in these compact stars. The crust-core interfacial mode is an oscillation mode in a neutron star and it depends mostly on the equation of the state of the matter in the crust-core transition region. This mode can be resonantly excited by the tidal field of an inspiraling-in BNS system, thereby affecting the emitted gravitational waves, and hence could be used to probe the equation of state in the crust-core transition region. In this work, we investigate in detail how the first-order phase transition inside the neutron star affects the properties of the crust-core interfacial mode, using a Newtonian fluid perturbation theory on a general relativistic background solution of the stellar structure. Two possible types of phase transitions are considered: (1) the phase transitions happen in the fluid core but near the crust-core interface, which results in density discontinuities; and (2) the strong interaction phase transitions in the dense core (as in the conventional hybrid star case). These phase transitions’ impacts on interfacial mode properties are discussed. In particular, the former phase transition has a minor effect on the M-R relation and the adiabatic tidal deformability, but can significantly affect the interfacial mode frequency and thereby could be probed using gravitational waves. For the BNS systems, we discuss the possible observational signatures of these phase transitions in the gravitational waveforms and their detectability. Our work enriches the exploration of the physical properties of the crust-core interfacial mode and provides a promising method for probing the phase transition using the seismology of a compact star.

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J. Zhu, C. Wang, C. Xia, et. al.
Tue, 22 Nov 22
83/83

Comments: 18 pages, 14 figures

Prospects for constraining interacting dark energy models from gravitational wave and gamma ray burst joint observation [CEA]

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http://arxiv.org/abs/2211.10087


With the measurement of the electromagnetic (EM) counterpart, a gravitational wave (GW) event could be treated as a standard siren. As a novel cosmological probe, the standard siren will bring significant implications for cosmology. In this paper, by considering the coincident detections of GW and associated $\gamma$ ray burst (GRB), we find that only about 400 GW bright standard sirens from binary neutron star mergers could be detected in a 10-year observation of the Einstein Telescope and the THESEUS satellite mission. Based on this mock sample, we investigate the implications of GW standard sirens on the interaction between dark energy and dark matter. In our analysis, four viable interacting dark energy (IDE) models, with interaction forms $Q=3\beta H \rho_{\mathrm{de}}$ and $Q=3 \beta H \rho_{\mathrm{c}}$, are considered. Compared with the traditional EM observational data such as CMB, BAO, and SN Ia, the combination of both GW and EM observations could effectively break the degeneracies between different cosmological parameters and provide more stringent cosmological fits. We also find that the GW data could play a more important role for determining the interaction in the models with $Q=3 \beta H \rho_{\mathrm{c}}$, compared with the models with $Q=3\beta H \rho_{\mathrm{de}}$.

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W. Hou, J. Qi, T. Han, et. al.
Mon, 21 Nov 22
6/66

Comments: 16 pages, 5 figures

Scalar scattering by black holes and wormholes [CL]

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http://arxiv.org/abs/2211.09886


We study the scattering of monochromatic planar scalar waves in a geometry that interpolates between the Schwarzschild solution, regular black holes and traversable wormhole spacetimes. We employ the partial waves approach to compute the differential scattering cross section of the regular black hole, as well as of the wormhole solutions. We compare our full numerical results with the classical geodesic scattering and the glory approximation, obtaining excellent agreement in the appropriate regime of validity of such approximations. We obtain that the differential scattering cross section for the regular black hole case is similar to the Schwarzschild result. Notwithstanding, the results for wormholes can be very distinctive from the black hole ones. In particular, we show that the differential scattering cross section for wormholes considerably decreases at large scattering angles for resonant frequencies.

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H. Junior, C. Benone and L. Crispino
Mon, 21 Nov 22
13/66

Comments: N/A

Exploring the Phase Diagram of V-QCD with Neutron Star Merger Simulations [HEAP]

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http://arxiv.org/abs/2211.10118


Determining the phase structure of Quantum Chromodynamics (QCD) and its Equation of State (EOS) at densities and temperatures realized inside neutron stars and their mergers is a long-standing open problem. The holographic V-QCD framework provides a model for the EOS of dense and hot QCD, which describes the deconfinement phase transition between a dense baryonic and a quark matter phase. We use this model in fully general relativistic hydrodynamic (GRHD) simulations to study the formation of quark matter and the emitted gravitational wave signal of binary systems that are similar to the first ever observed neutron star merger event GW170817.

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T. Demircik, C. Ecker, M. Järvinen, et. al.
Mon, 21 Nov 22
15/66

Comments: 8 pages, 3 figures, contribution to the proceedings of the XVth Quark Confinement and the Hadron Spectrum conference (1st-6th August 2022) at the University of Stavanger, Norway

Radiation from Global Topological Strings using Adaptive Mesh Refinement: Massive Modes [CEA]

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http://arxiv.org/abs/2211.10184


We implement adaptive mesh refinement (AMR) simulations of global topological strings using the public code, GRChombo. We perform a quantitative investigation of massive radiation from single sinusoidally displaced string configurations, studying a range of string widths defined by the coupling parameter $\lambda$ over two orders of magnitude, effectively varying the mass of radiated particles $m_H \sim \sqrt{\lambda}$. We perform an in-depth investigation into the effects of AMR on massive radiation emission, including radiation trapping and the refinement required to resolve high frequency modes. We use quantitative diagnostic tools to determine the eigenmode decomposition, showing a complex superposition of high frequency propagating modes with different phase and group velocities. We conclude that massive radiation is generally strongly suppressed relative to the preferred massless channel, with suppression increasing at lower amplitudes and higher $\lambda$. Only in extreme nonlinear regimes (e.g.\ with relative amplitude $\varepsilon \sim 1.5$ and $\lambda < 1$) do we observe massive and massless radiation to be emitted at comparable magnitude. We find that massive radiation is emitted in distinct high harmonics of the fundamental frequency of the string, and we demonstrate that, for the sinusoidal configurations studied, massive radiation is exponentially suppressed with $\sqrt{\lambda}$ (i.e. the particle mass). Finally, we place these results in the context of axions and gravitational waves produced by cosmological cosmic string networks, and note that AMR provides a significant opportunity to explore higher $\lambda$ (thin string) regimes whilst using fewer computational resources.

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A. Drew and E. Shellard
Mon, 21 Nov 22
24/66

Comments: 25 pages, 21 figures

Comparable dark matter and baryon abundances with a heavy dark sector [CL]

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http://arxiv.org/abs/2211.10359


We propose a scenario that explains the comparable abundances of dark matter (DM) and baryons without any coincidence in the corresponding particle masses. Here, DM corresponds to heavy “dark baryons” in a hidden MSSM-like dark sector, where the supersymmetry breaking scale can be several orders of magnitude larger than in the visible sector. In both sectors a baryon asymmetry is generated via the Affleck-Dine mechanism, and the smaller dark baryon-to-entropy ratio partially compensates the larger dark baryon masses to give similar densities in the two sectors. The large mass hierarchy also naturally results in an asymmetric reheating of these sequestered sectors. Moreover, this scenario predicts uncorrelated DM and baryon isocurvature perturbations.

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J. Rosa and D. Silva
Mon, 21 Nov 22
51/66

Comments: 5 pages, 2 figures

Two decades of optical timing of the shortest-period binary star system HM Cancri [SSA]

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http://arxiv.org/abs/2211.09834


The shortest-period binary star system known to date, RX J0806.3+1527 (HM Cancri), has now been observed in the optical for more than two decades. Although it is thought to be a double degenerate binary undergoing mass transfer, an early surprise was that its orbital frequency, $f_0$, is currently increasing as the result of gravitational wave radiation. This is unusual since it was expected that the mass donor was degenerate and would expand on mass loss, leading to a decreasing $f_0$. We exploit two decades of high-speed photometry to precisely quantify the trajectory of HM Cancri, allowing us to find that $\ddot f_0$ is negative, where $\ddot f_0~=~(-5.38\pm2.10)\times10^{-27}$ Hz s$^{-2}$. Coupled with our positive frequency derivative, we show that mass transfer is counteracting gravitational-wave dominated orbital decay and that HM Cancri will turn around within $2100\pm800\,$yrs from now. We present Hubble Space Telescope ultra-violet spectra which display Lyman-$\alpha$ absorption, indicative of the presence of hydrogen accreted from the donor star. We use these pieces of information to explore a grid of permitted donor and accretor masses with the Modules for Experiments in Stellar Astrophysics suite, finding models in good accordance with many of the observed properties for a cool and initially hydrogen-rich extremely-low-mass white dwarf ($\approx0.17\,$M$\odot$) coupled with a high accretor mass white dwarf ($\approx 1.0\,$M$\odot$). Our measurements and models affirm that HM~Cancri is still one of the brightest verification binaries for the Laser Interferometer Space Antenna spacecraft.

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J. Munday, T. Marsh, M. Hollands, et. al.
Mon, 21 Nov 22
58/66

Comments: 12 pages (+5 pages appendix), 9 figures, 6 tables. Accepted for publication in MNRAS

Model-independent search for anisotropies in stochastic gravitational-wave backgrounds and application to LIGO-Virgo's first three observing Runs [CL]

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http://arxiv.org/abs/2211.10010


A stochastic gravitational-wave (GW) background consists of a large number of weak, independent and uncorrelated events of astrophysical or cosmological origin. The GW power on the sky is assumed to contain anisotropies on top of an isotropic component, i.e., the angular monopole. Complementary to the LIGO-VIRGO-KAGRA (LVK) searches, we develop an efficient analysis pipeline to compute the maximum-likelihood anisotropic sky maps in stochastic backgrounds directly in the sky pixel domain using data folded over one sidereal day. We invert the full pixel-pixel correlation matrix in map-making of the GW sky, up to an optimal eigenmode cutoff decided systematically using simulations. In addition to modeled mapping, we implement a model-independent method to probe spectral shapes of stochastic backgrounds. Using data from LIGO-Virgo’s first three observing runs, we obtain upper limits on anisotropies as well as the isotropic monopole as a limiting case, consistent with the LVK results. We also set constraints on the spectral shape of the stochastic background using this novel model-independent method.

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L. Xiao, A. Renzini and A. Weinstein
Mon, 21 Nov 22
61/66

Comments: 10 pages, 9 figures

Jet-environment interplay in magnetized binary neutron star mergers [HEAP]

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http://arxiv.org/abs/2211.10135


GRB 170817A, the first short gamma-ray burst (sGRB) to be detected in coincidence with a gravitational wave signal, demonstrated that merging binary neutron star (BNS) systems can power collimated ultra-relativistic jets and, in turn, produce sGRBs. Moreover, it revealed that sGRB jets possess an intrinsic angular structure that is imprinted in the observable prompt and afterglow emission. Advanced numerical simulations represent the leading approach to investigate the physical processes underlying the evolution of sGRB jets breaking out of post-merger environments, and thus connect the final angular structure and energetics with specific jet launching conditions. In a previous paper, we carried out the first three-dimensional (3D) special-relativistic hydrodynamic simulations of incipient (top-hat) sGRB jets propagating across the realistic environment resulting from a general-relativistic (GR) hydrodynamic BNS merger simulation. While the above work marked an important step toward a consistent end-to-end description of sGRB jets from BNS mergers, those simulations did not account for the presence of magnetic fields, which are expected to play a key role. Here, we overcome this limitation, reporting the first 3D special-relativistic magnetohydrodynamic (MHD) simulation of a magnetized (structured and rotating) sGRB jet piercing through a realistic magnetized post-merger environment, wherein the initial conditions of the latter are directly imported from the outcome of a previous GR-MHD BNS merger simulation.

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A. Pavan, R. Ciolfi, J. Kalinani, et. al.
Mon, 21 Nov 22
63/66

Comments: 16 pages, 14 figures

The Primordial Particle Accelerator of the Cosmos [CL]

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http://arxiv.org/abs/2211.09674


In a previous paper we have shown that superluminal particles are allowed by the general relativistic theory of gravity provided that the metric is locally Euclidean. Here we calculate the probability density function of a canonical ensemble of superluminal particles as function of temperature. This is done for both space-times invariant under Lorentz symmetry group, and for space times invariant under an Euclidean symmetry group. Although only the Lorentzian metric is stable for normal matter density, an Euclidian metric can be created under special gravitational circumstances and persist in a limited region of space-time consisting of the very early universe which is characterized by extremely high densities and temperatures. Superluminal particles also allow attaining thermodynamic equilibrium at a shorter duration and also suggest a rapid expansion of the matter density, thus making mechanism such as inflation (which demands invoking and ad-hoc scalar field) redundant. This is in accordance with Occam’s razor.

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A. Yahalom
Fri, 18 Nov 22
7/70

Comments: 28 pages, 24 figures. arXiv admin note: text overlap with arXiv:gr-qc/0611124

Computing First-Passage Times with the Functional Renormalisation Group [CEA]

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http://arxiv.org/abs/2211.09649


We use Functional Renormalisation Group (FRG) techniques to analyse the behaviour of a spectator field, $\sigma$, during inflation that obeys an overdamped Langevin equation. We briefly review how a derivative expansion of the FRG can be used to obtain Effective Equations of Motion (EEOM) for the one- and two-point function and derive the EEOM for the three-point function. We show how to compute quantities like the amplitude of the power spectrum and the spectral tilt from the FRG. We do this explicitly for a potential with multiple barriers and show that in general many different potentials will give identical predictions for the spectral tilt suggesting that observations are agnostic to localised features in the potential. Finally we use the EEOM to compute first-passage time (FPT) quantities for the spectator field. The EEOM for the one- and two-point function are enough to accurately predict the average time taken $\left\langle \mathcal{N}\right\rangle$ to travel between two field values with a barrier in between and the variation in that time $\delta \mathcal{N}^2$. It can also accurately resolve the full PDF for time taken $\rho (\mathcal{N})$, predicting the correct exponential tail. This suggests that an extension of this analysis to the inflaton can correctly capture the exponential tail that is expected in models producing Primordial Black Holes.

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G. Rigopoulos and A. Wilkins
Fri, 18 Nov 22
25/70

Comments: 24 pages, 8 figures, 2 tables

Holographic origin of TCC and the Distance Conjecture [CL]

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http://arxiv.org/abs/2211.09128


One of the unique features of quantum gravity is the lack of local observables and the completeness of boundary observables. We show that the existence of boundary observables in scalar field cosmologies where $a(t)\sim t^{p}$ is equivalent to TCC, which implies $p\leq 1$. Moreover, the mass of weakly-coupled particles must decay like $m\lesssim t^{1-2p}$ to ensure that they yield non-trivial boundary observables. This condition can be expressed in terms of the scalar field that drives the cosmology as $m\lesssim\exp(-c\phi)$ where $c$ depends on the scalar potential. The strongest bound we find is achieved for $V\sim \exp(-2\phi/\sqrt{d-2})$ where $c=1/\sqrt{d-2}$. These results connect some of the most phenomenologically interesting Swampland conjectures to the most basic version of holography.

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A. Bedroya
Fri, 18 Nov 22
31/70

Comments: 34 pages, 6 figures

Bayesian implications for the primordial black holes from NANOGrav's pulsar-timing data by using the scalar induced gravitational waves [CEA]

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http://arxiv.org/abs/2211.09450


Assuming the common-spectrum process in the NANOGrav 12.5-year dataset has an origin of scalar induced gravitational waves, we study the enhancement of primordial curvature perturbations and the mass function of primordial black holes, by performing the Bayesian parameter inference for the first time. We obtain lower limits on the spectral amplitude, i.e. $\mathcal{A}\gtrsim10^{-2}$ at 95\% confidence level, when assuming the power spectrum of primordial curvature perturbations to follow a log-normal distribution function with width $\sigma$. In the limit of $\sigma\rightarrow0$, we find that the primordial black holes with $10^{-3}-10^{-2}$ solar mass are allowed to compose at least a fraction of dark matter. Such a mass range would be shifted to more massive regimes for larger values of $\sigma$, e.g. to a regime of $10^{-2}-10^{-1}$ solar mass for $\sigma=1$. We expect that planned gravitational-wave experiments are capable to reach at least $\mathcal{A}\sim10^{-4}$ and search for the primordial black holes over the whole parameter space. In addition, importance of multi-band detector networks is emphasized to accomplish our theoretical expectation.

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Z. Zhao and S. Wang
Fri, 18 Nov 22
36/70

Comments: 16 pages, 5 figures, 1 table

Evolution and Possible Forms of Primordial Antimatter and Dark Matter celestial objects [CL]

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http://arxiv.org/abs/2211.09579


The structure and evolution of Primordial Antimatter domains and Dark matter objects are analysed. Relativistic low-density antimatter domains are described. The Relativistic FRW perfect-fluid solution is found for the characterization of i) ultra-high density antimatter domains, ii) high-density antimatter domains, and iii) dense anti-matter domains. The possible sub-domains structures is analyzed. The structures evolved to the time of galaxy formation are outlined. Comparison is given with other primordial celestial objects. The features of antistars are outlined. In the case of WIMP dark matter clumps, the mechanisms of their survival to the present time are discussed. The cosmological features of neutrino clumping due to fifth force are examined.

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M. Khlopov and O. Lecian
Fri, 18 Nov 22
43/70

Comments: Prepared for Proceedings of XXV Bled Workshop “What comes beyond the Standard models?”

Ending inflation with a bang: Higgs vacuum decay in $R^2$ gravity [CEA]

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http://arxiv.org/abs/2211.09244


According to the current experimental data, the Higgs vacuum appears to be metastable due to the development of a second lower ground state in its potential. Consequently, vacuum decay would induce the nucleation of true vacuum bubbles with catastrophic consequences for our Universe and therefore we are motivated to study possible stabilising mechanisms in the early universe. In our latest investigation (2207.00696), we studied the electroweak metastability in the context of the observationally favoured model of Starobinsky inflation. Following the motivation and techniques from our first study (2011.037633), we obtained constraints on the Higgs curvature coupling $\xi$, while embedding the SM on the modified gravity scenario $R+R^2$, which introduces Starobinsky inflation naturally. This had significant repercussions for the effective Higgs potential in the form of additional negative terms that destabilize the false vacuum. Another important aspect lay in the definition for the end of inflation, as bubble nucleation is most prominent during its very last moments. Our results dictated that these stronger lower $\xi$-bounds are very sensitive to the final moments of inflation, where spacetime deviates increasingly from de Sitter.

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A. Mantziris
Fri, 18 Nov 22
44/70

Comments: 6 pages, 2 figures, based on the parallel talk at the International Conference of High Energy Physics (6-13 July 2022) hosted by the INFN sections and Universities of Bologna and Ferrara

How does SU($N$)-natural inflation isotropize the universe? [CL]

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http://arxiv.org/abs/2211.09489


We study the homogeneous and anisotropic dynamics of pseudoscalar inflation coupled to an SU($N$) gauge field. To see how the initially anisotropic universe is isotropized in such an inflation model, we derive the equations to obtain axisymmetric SU($N$) gauge field configurations in Bianchi type-I geometry and discuss a method to identify their isotropic subsets which are the candidates of their late-time attractor. Each isotropic solution is characterized by the corresponding SU(2) subalgebra of the SU($N$) algebra. It is shown numerically that the isotropic universe is a universal late-time attractor in the case of the SU(3) gauge field. Interestingly, we find that a transition between the two distinct gauge-field configurations characterized by different SU(2) subalgebras can occur during inflation. We clarify the conditions for this to occur. This transition could leave an observable imprint on the CMB and the primordial gravitational wave background.

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T. Murata, T. Fujita and T. Kobayashi
Fri, 18 Nov 22
49/70

Comments: 17 pages, 7 figures

Effects of the matter Lagrangian degeneracy in $f(Q,T)$ gravity [CL]

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http://arxiv.org/abs/2211.09042


In this paper, we investigated the theoretical and cosmological effects of the matter Lagrangian degeneracy in an extension of the Symmetric Teleparallel Equivalent of General Relativity, denoted as $f (Q, T )$ gravity. This degeneracy comes from the fact that both $\mathcal{L}_m = p$ and $\mathcal{L}_m = -\rho$ can give rise to the stress-energy tensor of a perfect fluid. The $f(Q,T)$ equations depend on the form of the matter Lagrangian and hence they also have a degeneracy that has influence on the density evolution of dust matter and radiation, on the form of the generalized Friedmann equations and also shows changes in the cosmological parameters confidence regions when performing Monte Carlo Markov Chains analyses. Our results suggest that since changing the matter Lagrangian causes different theoretical and cosmological results, future studies in $f(Q,T)$ gravity should consider both forms of the matter Lagrangians to account for the different mathematical and observational results.

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J. Nájera and C. Alvarado
Thu, 17 Nov 22
6/63

Comments: Accepted for publication in Physics of the Dark Universe

Dark Matter or Regular Matter in Neutron Stars? How to tell the difference from the coalescence of compact objects [HEAP]

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http://arxiv.org/abs/2211.08590


The mirror twin Higgs model is a candidate for (strongly-interacting) complex dark matter, which mirrors SM interactions with heavier quark masses. A consequence of this model are mirror neutron stars — exotic stars made entirely of mirror matter, which are significantly smaller than neutron stars and electromagnetically dark. This makes mergers of two mirror neutron stars detectable and distinguishable in gravitational wave observations, but can we observationally distinguish between regular neutron stars and those that may contain some mirror matter? This is the question we study in this paper, focusing on two possible realizations of mirror matter coupled to standard model matter within a compact object: (i) mirror matter captured by a neutron star and (ii) mirror neutron star-neutron star coalescences. Regarding (i), we find that (non-rotating) mirror-matter-admixed neutron stars no longer have a single mass-radius sequence, but rather exist in a two-dimensional mass-radius plane. Regarding (ii), we find that binary systems with mirror neutron stars would span a much wider range of chirp masses and completely different binary Love relations, allowing merger remnants to be very light black holes. The implications of this are that gravitational wave observations with advanced LIGO and Virgo, and X-ray observations with NICER, could detect or constrain the existence of mirror matter through searches with wider model and parameter priors.

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M. Hippert, E. Dillingham, H. Tan, et. al.
Thu, 17 Nov 22
17/63

Comments: 22 pages, 16 figures

Adapting to noise distribution shifts in flow-based gravitational-wave inference [CL]

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http://arxiv.org/abs/2211.08801


Deep learning techniques for gravitational-wave parameter estimation have emerged as a fast alternative to standard samplers $\unicode{x2013}$ producing results of comparable accuracy. These approaches (e.g., DINGO) enable amortized inference by training a normalizing flow to represent the Bayesian posterior conditional on observed data. By conditioning also on the noise power spectral density (PSD) they can even account for changing detector characteristics. However, training such networks requires knowing in advance the distribution of PSDs expected to be observed, and therefore can only take place once all data to be analyzed have been gathered. Here, we develop a probabilistic model to forecast future PSDs, greatly increasing the temporal scope of DINGO networks. Using PSDs from the second LIGO-Virgo observing run (O2) $\unicode{x2013}$ plus just a single PSD from the beginning of the third (O3) $\unicode{x2013}$ we show that we can train a DINGO network to perform accurate inference throughout O3 (on 37 real events). We therefore expect this approach to be a key component to enable the use of deep learning techniques for low-latency analyses of gravitational waves.

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J. Wildberger, M. Dax, S. Green, et. al.
Thu, 17 Nov 22
21/63

Comments: N/A

Chiral Gravitational Waves in Palatini Chern-Simons [CL]

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http://arxiv.org/abs/2211.08925


We study the parity-breaking higher-curvature gravity theory of Chern-Simons (CS), using the Palatini formulation in which the metric and connection are taken to be independent fields. We first show that Palatini CS gravity leads to first-order derivative equations of motion and thus avoid the typical instabilities of CS gravity in the metric formalism. As an initial application, we analyze the cosmological propagation of gravitational waves (GWs) in Palatini CS gravity. We show that, due to parity breaking, the polarizations of GWs suffer two effects during propagation: amplitude birefringence (which changes the polarization ellipticity) and velocity birefringence (which rotates the polarization plane). While amplitude birefringence is known to be present in CS gravity in the metric formalism, velocity birefringence is not present in metric CS gravity, but now appears in Palatini CS due to the fact that left-handed and right-handed GW polarizations have a different dispersion relation. In the approximation of small deviations from General Relativity (GR), we do find however that velocity birefringence appears at least quadratically in the CS coupling parameter $\alpha$, while amplitude birefringence appears linearly in $\alpha$. This means that amplitude birefringence will be the most relevant effect in Palatini CS and hence this model will behave similarly to metric CS. We confirm this by applying current constraints on amplitude and velocity birefringence to Palatini CS, and showing that those from amplitude birefringence give the tightest bounds.

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F. Sulantay, M. Lagos and M. Bañados
Thu, 17 Nov 22
28/63

Comments: 11 pages, 1 figure

Normalizing Flows for Hierarchical Bayesian Analysis: A Gravitational Wave Population Study [IMA]

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http://arxiv.org/abs/2211.09008


We propose parameterizing the population distribution of the gravitational wave population modeling framework (Hierarchical Bayesian Analysis) with a normalizing flow. We first demonstrate the merit of this method on illustrative experiments and then analyze four parameters of the latest LIGO data release: primary mass, secondary mass, redshift, and effective spin. Our results show that despite the small and notoriously noisy dataset, the posterior predictive distributions (assuming a prior over the parameters of the flow) of the observed gravitational wave population recover structure that agrees with robust previous phenomenological modeling results while being less susceptible to biases introduced by less-flexible distribution models. Therefore, the method forms a promising flexible, reliable replacement for population inference distributions, even when data is highly noisy.

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D. Ruhe, K. Wong, M. Cranmer, et. al.
Thu, 17 Nov 22
36/63

Comments: N/A

EBWeyl: a Code to Invariantly Characterize Numerical Spacetimes [CL]

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http://arxiv.org/abs/2211.08133


In order to invariantly characterise spacetimes resulting from cosmological simulations in numerical relativity, we present two different methodologies to compute the electric and magnetic parts of the Weyl tensor, $E_{\alpha\beta}$ and $B_{\alpha\beta}$, from which we construct scalar invariants and the Weyl scalars. The first method is geometrical, computing these tensors in full from the metric, and the second uses the 3+1 slicing formulation. We developed a code for each method and tested them on five analytic metrics, for which we derived $E_{\alpha\beta}$ and $B_{\alpha\beta}$ and the various scalars constructed from them with computer algebra software. We find excellent agreement between the analytic and numerical results. The slicing code outperforms the geometrical code for computational convenience and accuracy; on this basis we make it publicly available in github with the name EBWeyl [ https://github.com/robynlm/ebweyl ]. We emphasize that this post-processing code is applicable to numerical spacetimes in any gauge.

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R. Munoz and M. Bruni
Thu, 17 Nov 22
40/63

Comments: 27 pages, 8 figures, EBWeyl can be found at this https URL

On Warm Natural Inflation and Planck 2018 constraints [CL]

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http://arxiv.org/abs/2211.07775


We investigate Natural Inflation with non-minimal coupling to gravity, characterized either by a quadratic or a periodic term, within the Warm Inflation paradigm during the slow roll stage, in both strong and weak dissipation limits, and show that it can accommodate the spectral index $n_s$ and tensor-to-scalar ratio $r$ observables given by Planck 2018 constraints, albeit with a too small value of the e-folding number to solve the horizon problem, providing thus only a partial solution to Natural Inflation issues.

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M. AlHallak, K. Said, N. CHAMOUN, et. al.
Wed, 16 Nov 22
5/76

Comments: pdflatex, 12 pages, 3 figures

On the sound velocity bound in neutron stars [HEAP]

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http://arxiv.org/abs/2211.07874


It has been suggested in the literature that the sound velocity of the nuclear matter $v_s$ violates the so-called sound velocity bound $v_s \le c/\sqrt{3}$ at high density, where $c$ is the speed of light. In this paper, we revisit this issue and confront the current measurements of mass, radius, and tidal deformability of neutron stars with $10^5$ different equations of state which are parametrized at low density and saturates the sound velocity bound beyond twice the saturation density where the equation of state has not been constrained yet, by which we can conservatively obtain the maximum mass of the neutron stars compatible both with the observed properties of neutron stars and the sound velocity bound. We find that majority of the models are eliminated by the incompatibility with the observations and, especially, the recently detected massive pulsar ($2.35\pm 0.17 M_\odot$) is hardly realized by our simulations. Our study strongly supports the violation of the sound velocity bound.

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S. Roy and T. Suyama
Wed, 16 Nov 22
15/76

Comments: 14 pages, 5 figures

Non-perturbative non-Gaussianity and primordial black holes [CEA]

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http://arxiv.org/abs/2211.08348


We present a non-perturbative method for calculating the abundance of primordial black holes given an arbitrary one-point probability distribution function for the primordial curvature perturbation, $P(\zeta)$. A non-perturbative method is essential when considering non-Gaussianities that cannot be treated using a conventional perturbative expansion. To determine the full statistics of the density field, we relate $\zeta$ to a Gaussian field by equating the cumulative distribution functions. We consider two examples: a specific local-type non-Gaussian distribution arising from ultra slow roll models, and a general piecewise model for $P(\zeta)$ with an exponential tail. We demonstrate that the enhancement of primordial black hole formation is due to the intermediate regime, rather than the far tail. We also show that non-Gaussianity can have a significant impact on the shape of the primordial black hole mass distribution.

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A. Gow, H. Assadullahi, J. Jackson, et. al.
Wed, 16 Nov 22
16/76

Comments: 8 pages, 2 figures

BiGONLight: a new package for computing optical observables in Numerical Relativity [CL]

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http://arxiv.org/abs/2211.08336


The investigation of relativistic effects in the most general way requires a unified treatment of light propagation in cosmology. This goal can be achieved with the new interpretation of the geodesic deviation equation in terms of the bilocal geodesic operators (BGO). The BGO formalism extends the standard formulation, providing a unified framework to describe all possible optical phenomena due to the interaction between light and spacetime curvature. In my dissertation, I present {\tt BiGONLight}, a {\tt Mathematica} package that applies the BGO formalism to study light propagation in numerical relativity. The package encodes the 3+1 bilocal geodesic operators framework as a collection of {\tt Mathematica} functions. The inputs are the spacetime metric plus the kinematics of the observer and the source in the form of the 3+1 quantities, which may come directly from a numerical simulation or can be provided by the user as analytical components. These data are then used for ray tracing and computing the BGOs in a completely general way, i.e. without relying on symmetries or specific coordinate choices. The primary purpose of the package is the computation of optical observables in arbitrary spacetimes. The uniform theoretical framework of the BGO formalism allows for the extraction of multiple observables within a single computation, while the {\tt Wolfram} language provides a flexible computational framework that makes the package highly adaptable to perform both numerical and analytical studies of light propagation.

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M. Grasso
Wed, 16 Nov 22
18/76

Comments: Thesis submitted to the Center for Theoretical Physics for the degree of Doctor of Philosophy in Physics

Estimating and detecting random processes on the unit circle [CL]

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http://arxiv.org/abs/2211.07884


The problem of detecting a sinusoidal signal with randomly varying frequency has a long history. It is one of the core problems in signal processing, arising in many applications including, for example, underwater acoustic frequency line tracking, demodulation of FM radio communications, laser phase drift in optical communications and, recently, continuous gravitational wave astronomy. In this paper we describe a Markov Chain Monte Carlo based procedure to compute a specific detection posterior density. We demonstrate via simulation that our approach results in an up to $25$ percent higher detection rate than Hidden Markov Model based solutions, which are generally considered to be the leading techniques for these problems.

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C. Liu, S. Suvorova, R. Evans, et. al.
Wed, 16 Nov 22
33/76

Comments: 6 pages, 4 figures, 12th IFAC Symposium on Nonlinear Control Systems

A Tilt Instability in the Cosmological Principle [CEA]

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http://arxiv.org/abs/2211.08093


We show that the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) framework has an instability towards the growth of fluid flow anisotropies, even if the Universe is accelerating. This flow (tilt) instability in the matter sector is invisible to Cosmic No-Hair Theorem-like arguments, which typically only flag shear anisotropies in the metric. We illustrate our claims in the setting of “dipole cosmology”, the maximally Copernican generalization of FLRW that can accommodate a flow. Simple models are sufficient to show that the cosmic flow need not track the shear, even in the presence of a positive cosmological constant. We also emphasize that the growth of the tilt hair is fairly generic if the total equation of state $w(t) \rightarrow -1$ at late times (as it does in standard cosmology), irrespective of the precise model of dark energy.

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C. Krishnan, R. Mondol and M. Sheikh-Jabbari
Wed, 16 Nov 22
34/76

Comments: 5 pages, 4 figures

Casimir Tests of Scalar-Tensor Theories [CL]

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http://arxiv.org/abs/2211.07840


We compute bounds and forecasts on screened modified gravity theories, specialising to the chameleon model in Casimir force experiments. In particular, we investigate the classical interaction between a plate and sphere subject to a screened interaction of the chameleon type. We compare numerical simulations of the field profile and the classical pressure exerted on the sphere to analytical approximations for these non-linear field theories. In particular, we focus on the proximity force approximation (PFA) and show that, within the range of sphere sizes $R$ and plate-sphere distance $D$ simulated numerically, the PFA does not reproduce the numerical results. This differs from the case of linear field theories such as Newtonian gravity and a Yukawa model where the PFA coincides with the exact results. We show that for chameleon theories, the screening factor approximation (SFA) whereby the sphere is modelled as a screened sphere embedded in the external field due to the plates, fares better and can be used in the regime $D\gtrsim R$ to extract constraints and forecasts from existing and forthcoming data. In particular, we forecast that future Casimir experiments would corroborate the closing of the parameter space for the simplest of chameleon models at the dark energy scale.

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P. Brax, A. Davis and B. Elder
Wed, 16 Nov 22
42/76

Comments: 27 pages, 6 figures

Anisotropic constant-roll k-inflation model [CL]

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http://arxiv.org/abs/2211.08032


In this paper, we would like to figure out whether a k-inflation model admits the Bianchi type I metric as its inflationary solution under a constant-roll condition in the presence of the supergravity motivated coupling between scalar and vector fields, $f^2(\phi)F_{\mu\nu}F^{\mu\nu}$. As a result, some novel anisotropic inflationary solutions are shown to appear along with a power-law one in this scenario. Furthermore, these solutions are numerically confirmed to be attractive, in contrast to the prediction of the Hawking’s cosmic no-hair conjecture.

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D. Nguyen, T. Pham, T. Le, et. al.
Wed, 16 Nov 22
46/76

Comments: 15 pages, 11 figures. To appear in Communications in Physics (2023), a well-established physics journal of Vietnam. Comments are welcome

Constraining the Lorentz-Violating Bumblebee Vector Field with Big Bang Nucleosynthesis and Gravitational Baryogenesis [CL]

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http://arxiv.org/abs/2211.07934


By keeping the cosmological principle i.e., an isotropic and homogeneous universe, we consider the cosmology of a vector-tensor theory of gravitation known as the \textit{bumblebee} model. In this model a single Lorentz-violating timelike vector field with a nonzero vacuum expectation value (VEV) couples to the Ricci tensor and scalar, as well. Taking the ansatz $B(t)\sim t^\beta$ for the time evolution of the vector field we derive the relevant dynamic equations of the Universe, where $\beta$ is a free parameter. In particular, by employing observational data coming from the Big Bang Nucleosynthesis (BBN) and the matter-antimatter asymmetry in the Baryogenesis era, we impose some constraints on the VEV of the bumblebee timelike vector field i.e., $\xi b^2$, and the exponent parameter $\beta$. The former and the latter limit the size of Lorentz violation, and the rate of the time evolution of the background Lorentz-violating bumblebee field, respectively.

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M. Khodadi, G. Lambiase and A. Sheykhi
Wed, 16 Nov 22
51/76

Comments: 16 pages (two columns), 5 figures

Cosmic decoherence: primordial power spectra and non-Gaussianities [CEA]

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http://arxiv.org/abs/2211.07598


We study the effect of quantum decoherence on the inflationary cosmological perturbations. This process might imprint specific observational signatures revealing the quantum nature of the inflationary mechanism being related to the longstanding issue of the quantum-to-classical transition of inflationary fluctuations. Several works have investigated the effect of quantum decoherence on the statistical properties of primordial fluctuations. In particular, it has been shown that cosmic decoherence leads to corrections to the curvature power spectrum predicted by standard slow-roll inflation. Equally interesting, a non zero curvature trispectrum has been shown to be purely induced by cosmic decoherence, but surprisingly, decoherence seems not to generate any bispectrum. We further develop such an analysis by adopting a generalized form of the pointer observable, showing that decoherence does induce a non vanishing curvature bispectrum and providing a specific underlying concrete physical process. Present constraints on primordial bispectra allow to put an upper bound on the strength of the environment-system interaction. In full generality, the decoherence-induced bispectrum can be scale dependent provided one imposes the corresponding correction to the power spectrum to be scale independent. Such scale dependence on the largest cosmological scales might represent a distinctive imprint of the quantum decoherence process taking place during inflation. We also provide a criterion that allows to understand when cosmic decoherence induces scale independent corrections, independently of the type of environment considered. As a final result, we study the effect of cosmic decoherence on tensor perturbations and we derive the decoherence corrected tensor-to-scalar perturbation ratio. In specific cases, decoherence induces a blue tilted correction to the standard tensor power spectrum.

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A. Hammou and N. Bartolo
Tue, 15 Nov 22
8/103

Comments: 56 pages, 6 figures

The Galactic Center as a laboratory for theories of gravity and dark matter [GA]

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http://arxiv.org/abs/2211.07008


The Galactic Center of the Milky Way, thanks to its proximity, allows to perform astronomical observations that investigate physical phenomena at the edge of astrophysics and fundamental physics. As such, our Galactic Center offers a unique laboratory to test gravity. In this review we provide a general overview of the history of observations of the GC, focusing in particular on the smallest-observable scales, and on the impact that such observations have on our understanding of the underlying theory of gravity in the surrounding of a massive compact object.

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M. Laurentis, I. Martino and R. Monica
Tue, 15 Nov 22
11/103

Comments: Comments and suggestions are welcome

Impact of magnetism on gravitational waves emitted by compact galactic binaries in quasi-circular orbits [CL]

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http://arxiv.org/abs/2211.07431


The LISA (Laser Interferometer Space Antenna) mission will observe in the low frequency band from 0.1 mHz to 1 Hz. In this regime, we expect the galactic binaries to be the dominant (by number) sources of gravitational waves signal. Considering that galactic binaries are composed of the most magnetized astrophysical objects in the universe (i.e., the white dwarfs and the neutron stars), LISA is expected to bring new informations about the origin and the nature of magnetism inside degenerated stars. Currently, the data processing assumes that the galactic binary systems are non-magnetic and in circular orbits which can potentially biased the determination of the parameters of the sources and also the calibration of the detector. In this work, we investigate the impact of magnetism on gravitational waves emitted by compact galactic binaries assuming quasi-circular orbits.

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A. Bourgoin, E. Savalle, C. Poncin-Lafitte, et. al.
Tue, 15 Nov 22
15/103

Comments: 4 pages, 2 figures, proceedings SF2A

Eccentricity or spin precession? Distinguishing subdominant effects in gravitational-wave data [HEAP]

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http://arxiv.org/abs/2211.07528


Eccentricity and spin precession are key observables in gravitational-wave astronomy, encoding precious information about the astrophysical formation of compact binaries together with fine details of the relativistic two-body problem. However, the two effects can mimic each other in the emitted signals, raising issues around their distinguishability. Since inferring the existence of both eccentricity and spin precession simultaneously is — at present — not possible, current state-of-the-art analyses assume that either one of the effects may be present in the data. In such a setup, what are the conditions required for a confident identification of either effect? We present simulated parameter inference studies in realistic LIGO/Virgo noise, studying events consistent with either spin precessing or eccentric binary black hole coalescences and recovering under the assumption that either of the two effects may be at play. We quantify how the distinguishability of eccentricity and spin precession increases with the number of visible orbital cycles, confirming that the signal must be sufficiently long for the two effects to be separable. The threshold depends on the injected source, with inclination, eccentricity, and effective spin playing crucial roles. In particular, for injections similar to GW190521, we find that it is impossible to confidently distinguish eccentricity from spin precession.

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I. Romero-Shaw, D. Gerosa and N. Loutrel
Tue, 15 Nov 22
19/103

Comments: 7 pages, 1 figure. Comments welcome

Mass of compact stars in f(T) gravity [CL]

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http://arxiv.org/abs/2211.07418


The mass of compact objects in General Relativity (GR), which as is well known, is obtained via the Tolman – Oppenheimer – Volkov (TOV) equations, is a well defined quantity. However, in alternative gravity, this is not in general the case. In the particular case of $f(T)$ gravity, where $T$ is the scalar torsion, some authors consider that this is still an open question, since it is not guaranteed that the same equation used in TOV GR holds. In this paper we consider such an important issue and compare different ways to calculate the mass of compact objects in $f(T)$ gravity. In particular, we argue that one of them, the asymptotic mass, may be the most appropriate way to calculate mass in this theory. We adopt realistic equations of state in all the models presented in this article.

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J. Araujo and H. Fortes
Tue, 15 Nov 22
32/103

Comments: N/A

A Numerical Approach to the Exterior Solution of Spherically Symmetric and Static Configuration in Scalar-Tensor Theories [CL]

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http://arxiv.org/abs/2211.06079


We examine the exterior solution of spherically symmetric and static configuration in scalar-tensor theories by solving the differential equations numerically and fitting the resulting data in the interested region. Our main purpose in this work is to find out approximate analytical expressions which are independent of the parameters of a model as much as possible. To this end, we use the nonminimally coupled scalar field with zero potential as our sample model. We determine the forms of the mass and the metric functions in terms of the scalar field up to a certain order of accuracy. Then, we define a function for the scalar field that contains only the mass and the radius of the configuration as the parameters.

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A. Arapoğlu, S. Çağan and A. Yükselci
Tue, 15 Nov 22
33/103

Comments: 15 pages, 7 figures

Rapid Hierarchical Inference of Neutron Star Equation of State from multiple Gravitational Wave Observations of Binary Neutron Star Coalescences [CL]

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http://arxiv.org/abs/2211.06435


Bayesian hierarchical inference of phenomenological parameterized neutron star equations of state (EoS) from multiple gravitational wave observations of binary neutron star mergers is of fundamental importance in improving our understanding of neutron star structure, the general properties of matter at supra nuclear densities and the strong nuclear force. However, such an analysis is computationally costly as it is unable to re-use single-event EoS agnostic parameter estimation runs that are carried out regardless for generating gravitational wave transient catalogs. With the number of events expected to be observable during the 4th observing run (O4) of LIGO/Virgo/KAGRA, this problem can only be expected to worsen. We develop a novel and robust algorithm for rapid and computationally cheap hierarchical inference of parameterized EoSs from gravitational wave data which re-uses single event EoS agnostic parameter estimation samples to significantly reduce computational cost. We efficiently include a priori knowledge of neutron star physics as Bayesian priors on the EoS parameters. The high speed and low computational cost of our method allow for efficient re-computation of EoS inference every time a new binary neutron star event is discovered or whenever new observations and theoretical discoveries change the prior on EoS parameters. We test our method on both real and simulated gravitational wave data to demonstrate its accuracy. We show that our computationally cheap method produces EoS constraints that are completely consistent with existing analysis for real data, the chosen fiducial EoS for simulated data. Armed with our fast analysis scheme, we also study the variability of EoS constraints with binary neutron star properties for sets of simulated events drawn in different signal-to-noise ratio and mass ranges.

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A. Ray, M. Camilo, J. Creighton, et. al.
Tue, 15 Nov 22
43/103

Comments: N/A

General-relativistic neutrino-radiation magnetohydrodynamics simulation of seconds-long black hole-neutron star mergers: Dependence on initial magnetic field strength, configuration, and neutron-star equation of state [HEAP]

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http://arxiv.org/abs/2211.07158


Numerical-relativity simulations for seconds-long black hole-neutron star mergers are performed to obtain a self-consistent picture starting from the inspiral and the merger throughout the post-merger stages for a variety of setups. Irrespective of the initial and computational setups, we find qualitatively universal evolution processes: The dynamical mass ejection takes place together with a massive accretion disk formation after the neutron star is tidally disrupted; Subsequently, the magnetic field in the accretion disk is amplified by the magnetic winding, Kelvin-Helmholtz instability, and magnetorotational instability, which establish a turbulent state inducing the dynamo and angular momentum transport; The post-merger mass ejection by the effective viscous effects stemming from the magnetohydrodynamics turbulence sets in at $\sim300$-$500$ ms after the merger and continues for several hundred ms; A magnetosphere near the black-hole spin axis is developed and the collimated strong Poynting flux is generated with its lifetime of $\sim0.5$-$2$ s. The model of no equatorial-plane symmetry shows the reverse of the magnetic-field polarity in the magnetosphere, which is caused by the dynamo associated with the magnetorotational instability in the accretion disk. The model with initially toroidal fields shows the tilt of the disk and magnetosphere in the late post-merger stage because of the anisotropic post-merger mass ejection. These effects could terminate the strong Poynting-luminosity stage within the timescale of $\sim0.5$-$2$ s.

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K. Hayashi, K. Kiuchi, K. Kyutoku, et. al.
Tue, 15 Nov 22
46/103

Comments: 29 pages, 19 figures, and 1 table. arXiv admin note: text overlap with arXiv:2111.04621

Inferring Interference: Identifying a Perturbing Tertiary with Eccentric Gravitational Wave Burst Timing [CL]

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http://arxiv.org/abs/2211.07278


Binary black holes may form and merge dynamically. These binaries are likely to become bound with high eccentricities, resulting in a burst of gravitational radiation at their point of closest approach. When such a binary is perturbed by a third body, the evolution of the orbit is affected, and gravitational-wave burst times are altered. The bursts times therefore encode information about the tertiary. In order to extract this information, we require a prescription for the relationship between the tertiary properties and the gravitational-wave burst times. In this paper, we demonstrate a toy model for the burst times of a secular three-body system. We show how Bayesian inference can be employed to deduce the tertiary properties when the bursts are detected by next-generation ground-based gravitational-wave detectors. We study the bursts from an eccentric binary with a total mass of $60$ M$\odot$ orbiting an $6 \times 10^{8}$ M$\odot$ supermassive black hole. When we assume no knowledge of the eccentric binary, we are unable to tightly constrain the existence or properties of the tertiary, and we recover biased posterior probability distributions for the parameters of the eccentric binary. However, when the properties of the binary are already well-known — as is likely if the late inspiral and merger are also detected — we are able to more accurately infer the mass of the perturber, $m_3$, and its distance from the binary, $R$. When we assume measurement precision on the binary parameters consistent with expectations for next-generation gravitational-wave detectors, we can be greater than $90\%$ confident that the binary is perturbed. Even in this case, there are large statistical errors on $m_3$ and $R$, which stem from a correlation between $m_3$ and $R$ in the simple toy model; this correlation may be broken in future models allowing for non-secular evolution.

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I. Romero-Shaw, N. Loutrel and M. Zevin
Tue, 15 Nov 22
50/103

Comments: 19 pages, 9 figures. Comments welcome

Adaptive Analytical Ray Tracing of Black Hole Photon Rings [CL]

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http://arxiv.org/abs/2211.07469


Recent interferometric observations by the Event Horizon Telescope have resolved the horizon-scale emission from sources in the vicinity of nearby supermassive black holes. Future space-based interferometers promise to measure the ”photon ring”–a narrow, ring-shaped, lensed feature predicted by general relativity, but not yet observed–and thereby open a new window into strong gravity. Here we present AART: an Adaptive Analytical Ray-Tracing code that exploits the integrability of light propagation in the Kerr spacetime to rapidly compute high-resolution simulated black hole images, together with the corresponding radio visibility accessible on very long space-ground baselines. The code samples images on a nonuniform adaptive grid that is specially tailored to the lensing behavior of the Kerr geometry and therefore particularly well-suited to studying photon rings. This numerical approach guarantees that interferometric signatures are correctly computed on long baselines, and the modularity of the code allows for detailed studies of equatorial sources with complex emission profiles and time variability. To demonstrate its capabilities, we use AART to simulate a black hole movie of a stochastic, non-stationary, non-axisymmetric equatorial source; by time-averaging the visibility amplitude of each snapshot, we are able to extract the projected diameter of the photon ring and recover the shape predicted by general relativity.

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A. Cárdenas-Avendaño, A. Lupsasca and H. Zhu
Tue, 15 Nov 22
55/103

Comments: 39 pages, 16 figures

Reconciling cosmic dipolar tensions with a gigaparsec void [CEA]

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http://arxiv.org/abs/2211.06857


Recent observations indicate a $4.9\sigma$ tension between the CMB and quasar dipoles. This tension challenges the cosmological principle. We propose that if we live in a gigaparsec scale void, the CMB and quasar dipolar tension can be reconciled. This is because we are unlikely to live at the center of the void. And a 15% offset from the center will impact the quasars and CMB differently in their dipolar anisotropies. As we consider a large and thick void, our setup can also ease the Hubble tension.

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T. Cai, Q. Ding and Y. Wang
Tue, 15 Nov 22
68/103

Comments: 5 pages, 4 figures

Dynamical Friction due to fuzzy dark matter on satellites described by axisymmetric logarthmic potentials [CEA]

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http://arxiv.org/abs/2211.06752


A plausible dark matter candidate is an ultralight bosonic particle referred to as fuzzy dark matter. The equivalent mass-energy of the fuzzy dark matter boson is $\sim 10^{-22}$eV and has a corresponding de Broglie wavelength of kiloparsec scale, thus exhibiting wave behaviour in scales comparable to a galactic core, which could not appear in conventional cold dark matter models. The presence of fuzzy dark matter in galactic clusters will impact the motion of their members through dynamical friction. In this work, we present simulations of the dynamical friction on satellites traversing an initially uniform fuzzy dark matter halo. We focus on the satellites whose shapes are beyond spherical symmetry described by ellipsoidal and logarithmic potentials. We find that the wakes created on the fuzzy dark matter halo due to the passage of such satellites are qualitatively different from those generated by spherically symmetric ones. Furthermore, we quantify the dynamical friction coefficient for such systems, finding that the same satellite may experience a drag differing by a factor of $5$ depending on its ellipticity and the direction of motion. Finally, we find that the dynamical friction time-scale is close to Hubble time, assuming a satellite of $10^{11}$M${\odot}$ traversing at $10^{3}$km/s a FDM halo whose mean density is $\sim 10^6$M${\odot}$kpc$^{-3}$.

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A. Vitsos and K. Gourgouliatos
Tue, 15 Nov 22
78/103

Comments: 16 pages, 7 figures, comments are welcome

Beyond the linear tide: impact of the nonlinear tidal response of neutron stars on gravitational waveforms for binary inspirals [CL]

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http://arxiv.org/abs/2211.07002


Tidal interactions in coalescing binary neutron stars modify the dynamics of the inspiral, and hence imprint a signature on their gravitational-wave (GW) signals in the form of an extra phase shift. We need accurate models for the tidal phase shift in order to constrain the supranuclear equation of state from observations. In previous studies, GW waveform models were typically constructed by treating the tide as a linear response to a perturbing tidal field. In this work, we incorporate nonlinear corrections due to hydrodynamic three- and four-mode interactions and show how they can improve the accuracy and explanatory power of waveform models. We set up and numerically solve the coupled differential equations for the orbit and the modes, and analytically derive solutions of the system’s equilibrium configuration. Our analytical solutions agree well with the numerical ones up to the merger and involve only algebraic relations, allowing for fast phase shift and waveform evaluations for different equations of state over a large parameter space. We find that, at Newtonian order, nonlinear fluid effects can enhance the tidal phase shift by $\gtrsim 1\,{\rm radian}$ at a GW frequency of 1000 Hz, corresponding to a $10-20\%$ correction to the linear theory. The scale of the additional phase shift near the merger is consistent with the difference between numerical relativity and theoretical predictions that account only for the linear tide. Nonlinear fluid effects are thus important when interpreting the results of numerical relativity, and in the construction of waveform models for current and future GW detectors.

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H. Yu, N. Weinberg, P. Arras, et. al.
Tue, 15 Nov 22
88/103

Comments: 20 pages, 9 figures. To be submitted to MNRAS

Cosmological constraints on unimodular gravity models with diffusion [CEA]

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http://arxiv.org/abs/2211.07424


A discrete space-time structure lying at about the Planck scale may become manifest in the form of very small violations of the conservation of the matter energy-momentum tensor. In order to include such kind of violations, forbidden within the General Relativity framework, the theory of unimodular gravity seems as the simplest option to describe the gravitational interaction. In the cosmological context, a direct consequence of such violation of energy conservation might be heuristically viewed a “diffusion process of matter (both dark and ordinary)” into an effective dark energy term in Einstein’s equations, which leads under natural assumptions to an adequate estimate for the value of the cosmological constant. Previous works have also indicated that these kind of models might offer a natural scenario to alleviate the Hubble tension. In this work, we consider a simple model for thecosmological history including a late time occurrence of such energy violation and study the modifications of the predictions for the anisotropy and polarization of the Cosmic Microwave Background (CMB). We compare the model’s predictions with recent data from the CMB, Supernovae Type Ia, cosmic chronometers and Baryon Acoustic Oscillations. The results show the potential of this type of model to alleviate the Hubble tension.

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S. Landau, M. Benetti, A. Perez, et. al.
Tue, 15 Nov 22
89/103

Comments: 17 pages, 4 figures

Stability of domain wall network with initial inflationary fluctuations, and its implications for cosmic birefringence [CL]

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http://arxiv.org/abs/2211.06849


We study the formation and evolution of domain walls with initial inflationary fluctuations by numerical lattice calculations, correctly taking into account correlations on superhorizon scales. We find that, contrary to the widely-held claim, the domain wall network exhibits remarkable stability even when the initial distribution is largely biased toward one of the minima. This is due to the fact that the domain wall network retains information about initial conditions on superhorizon scales, and the scaling solution is not a local attractor in this sense. Applying this result to the axion-like particle domain wall, we show that it not only explains the isotropic cosmic birefringence suggested by the recent analysis but also predicts anisotropic cosmic birefringence that is nearly scale-invariant on large scales and can be probed by future CMB observations.

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D. Gonzalez, N. Kitajima, F. Takahashi, et. al.
Tue, 15 Nov 22
92/103

Comments: 7pages, 4figures

Self-consistent picture of the mass ejection from a one second-long binary neutron star merger leaving a short-lived remnant in general-relativistic neutrino-radiation magnetohydrodynamic simulation [HEAP]

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http://arxiv.org/abs/2211.07637


We perform a general-relativistic neutrino-radiation magnetohydrodynamic simulation of a one second-long binary neutron star merger on Japanese supercomputer Fugaku using about $72$ million CPU hours with $20,736$ CPUs. We consider an asymmetric binary neutron star merger with masses of $1.2$ and $1.5M_\odot$ and a `soft’ equation of state SFHo. It results in a short-lived remnant with the lifetime of $\approx 0.017$\,s, and subsequent massive torus formation with the mass of $\approx 0.05M_\odot$ after the remnant collapses to a black hole. For the first time, we confirm that after the dynamical mass ejection, which drives the fast tail and mildly relativistic components, the post-merger mass ejection from the massive torus takes place due to the magnetorotational instability-driven turbulent viscosity and the two ejecta components are seen in the distributions of the electron fraction and velocity with distinct features.

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K. Kiuchi, S. Fujibayashi, K. Hayashi, et. al.
Tue, 15 Nov 22
97/103

Comments: 8 pages, 5 figure, Supplement Material is this https URL

Using machine learning to compress the matter transfer function $T(k)$ [CEA]

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http://arxiv.org/abs/2211.06393


The linear matter power spectrum $P(k,z)$ connects theory with large scale structure observations in cosmology. Its scale dependence is entirely encoded in the matter transfer function $T(k)$, which can be computed numerically by Boltzmann solvers, and can also be computed semi-analytically by using fitting functions such as the well-known Bardeen-Bond-Kaiser-Szalay (BBKS) and Eisenstein-Hu (EH) formulae. However, both the BBKS and EH formulae have some significant drawbacks. On the one hand, although BBKS is a simple expression, it is only accurate up to $10\%$, which is well above the $1\%$ precision goal of forthcoming surveys. On the other hand, while EH is as accurate as required by upcoming experiments, it is a rather long and complicated expression. Here, we use the Genetic Algorithms (GAs), a particular machine learning technique, to derive simple and accurate fitting formulae for the transfer function $T(k)$. When the effects of massive neutrinos are also considered, our expression slightly improves over the EH formula, while being notably shorter in comparison.

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J. Orjuela-Quintana, S. Nesseris and W. Cardona
Mon, 14 Nov 22
3/69

Comments: 11 pages, 5 figures, 2 tables

Weighing neutrinos in dynamical dark energy cosmology with the logarithm parametrization and the oscillating parametrization [CL]

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http://arxiv.org/abs/2211.05956


We revisit the constraint results of different dynamical dark energy models including the Chevallier-Polarski-Linder (CPL) model with $w(z)=w_{0}+w_{1}\frac{z}{1+z}$ and the other two models with the logarithm parametrization of $w(z)=w_{0}+w_{1}\left(\frac{\ln (2+z)}{1+z}-\ln 2\right)$ and the oscillating parametrization of $w(z)=w_{0}+w_{1}\left(\frac{\sin(1+z)}{1+z}-\sin(1)\right)$. The advantage over the CPL model is that the latter two parametrizations for dark energy can explore the whole evolution history of the universe properly. Using the current latest mainstream observations including the cosmic microwave background and the baryon acoustic oscillation as well as the type Ia supernovae, we perform the $\chi^2$ statistic analysis to global fit these models, finding that the logarithm parametrization and the oscillating parametrization are slightly preferred against the CPL scenario. We constrain the total neutrino mass in these dynamical dark energy models. We find that, compared with those in the CPL model, much looser constraints on $\sum m_{\nu}$ are obtained in the logarithm model and the oscillating model. Consideration of the possible mass ordering of neutrinos reveals that the most stringent constraint on $\sum m_{\nu}$ appears in the degenerate hierarchy case. In addition, we confirm that the normal hierarchy case is slightly favored over the inverted one.

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R. Guo, T. Yao, X. Zhao, et. al.
Mon, 14 Nov 22
19/69

Comments: N/A

Synchronizing the EMRIs and IMRIs in AGN accretion disks [HEAP]

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http://arxiv.org/abs/2211.05798


Extreme-mass-ratio inspirals (EMRIs) and intermediate-mass-ratio inspirals (IMRIs) are important gravitational-wave (GW) sources for the Laser Interferometer Space Antenna (LISA). So far, their formation and evolution are considered to be independent, but recent theories suggest that stellar-mass black holes (sBHs) and intermediate-mass black hole (IMBHs) can coexist in the accretion disk of an active galactic nucleus (AGN), which indicates that EMRIs and IMRIs may form in the same place. Motivated by the fact that a gas giant migrating in a protoplanetary disk could trap planetesimals close to its orbit, we study in this paper a similar interaction between a gap-opening IMBH in an AGN disk and the sBHs surrounding it. We analyse the torques imposed on the sBHs by the disk as well as by the IMBH, and show that the sBHs can be trapped by the IMBH if they are inside the orbit of the IMBH. Then we implement the torques in our numerical simulations to study the migration of an outer IMBH and an inner sBH, both embedded in an AGN disk. We find that their migration is synchronized until they reach a distance of about ten Schwarzschild radii from the central supermassive black hole, where the pair breaks up due to strong GW radiation. This result indicates that LISA may detect an EMRI and an IMRI within several years from the same AGN. Such a GW source will bring rich information about the formation and evolution of sBHs and IMBHs in AGNs.

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P. Peng and X. Chen
Mon, 14 Nov 22
26/69

Comments: N/A

Early and late time cosmology: the $f(R)$ gravity perspective [CL]

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http://arxiv.org/abs/2211.06268


Discrepancies between observations at early and late cosmic epochs, and the vacuum energy problem associated with the interpretation of cosmological constant, are questioning the $\Lambda$CDM model. Motivated by these conceptual and observational facts, extensions of Einstein’s gravity are recently intensively considered in view of curing unsolved issues suffered by General Relativity at ultraviolet and infrared scales. Here, we provide a short overview of some aspects of $f(R)$ gravity, focusing, in particular, on cosmological applications. Specifically, Noether symmetries are adopted as a criterion to select viable models and investigate the corresponding dynamics. We thus find solutions to the cosmological field equations, analyzing the behaviour of selected models from the matter-dominated to the present epoch. Moreover, constraints coming from energy conditions and the so-called swampland criteria are also considered. In particular, we qualitatively discuss the possibility of $f(R)$ gravity to account for fixing cosmic tensions.

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F. Bajardi, R. D’Agostino, M. Benetti, et. al.
Mon, 14 Nov 22
30/69

Comments: 11 pages, 1 figure, Accepted for publication in EPJP

Gravitational Waves from Feebly Interacting Particles in a First Order Phase Transition [CL]

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http://arxiv.org/abs/2211.06405


First order phase transitions are well-motivated and extensively studied sources of gravitational waves (GWs) from the early Universe. The vacuum energy released during such transitions is assumed to be transferred primarily either to the expanding walls of bubbles of true vacuum, whose collisions source GWs, or to the surrounding plasma, producing sound waves and turbulence, which act as GW sources. In this Letter, we study an alternative possibility that has so far not been considered: the released energy gets transferred primarily to feebly interacting particles that do not admit a fluid description but simply free-stream individually. We develop the formalism to study the production of GWs from such configurations, and demonstrate that such GW signals have qualitatively distinct characteristics compared to conventional sources and are potentially observable with near-future GW detectors.

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R. Jinno, B. Shakya and J. Vis
Mon, 14 Nov 22
31/69

Comments: 5 pages+appendices, 8 figures

Circumventing the challenges in the choice of the non-conformal coupling function in inflationary magnetogenesis [CEA]

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http://arxiv.org/abs/2211.05834


[Abridged] As is well known, in order to generate magnetic fields of observed amplitudes during inflation, the conformal invariance of the electromagnetic field has to be broken by coupling it either to the inflaton or to the scalar curvature. Couplings to scalar curvature pose certain challenges even in slow roll inflation and it seems desirable to consider couplings to the inflaton. It can be shown that, in slow roll inflation, to generate nearly scale invariant magnetic fields of adequate strengths, the non-conformal coupling to the inflaton has to be chosen specifically depending on the inflationary model at hand. In a recent work, we had found that, when there arise sharp departures from slow roll inflation leading to strong features in the scalar power spectra, there inevitably arise sharp features in the spectra of the electromagnetic fields, unless the non-conformal coupling functions are extremely fine tuned. In particular, we had found that, if there occurs an epoch of ultra slow roll inflation, then the strength of the magnetic field over large scales can be severely suppressed. In this work, we examine whether these challenges can be circumvented in models of inflation involving two fields. We show that the presence of the additional scalar field allows us to construct coupling functions that lead to magnetic fields of required strengths even when there arise intermediate epochs of ultra slow roll inflation. However, we find that the features in the spectra of the magnetic fields that are induced due to the departures from slow roll inflation cannot be completely ironed out. We make use of the code MagCAMB to calculate the effects of the magnetic fields on the anisotropies in the cosmic microwave background and investigate if the spectra with features are broadly consistent with the current constraints.

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S. Tripathy, D. Chowdhury, H. Ragavendra, et. al.
Mon, 14 Nov 22
51/69

Comments: 21 pages, 8 figures