Tag Archives: General Relativity and Quantum Cosmology

The angular power spectrum of gravitational-wave transient sources as a probe of the large-scale structure [CEA]

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http://arxiv.org/abs/2305.02652


We present a new, simulation-based inference method to compute the angular power spectrum of the distribution of foreground gravitational-wave transient events. As a first application of this method, we use the binary black hole mergers observed during the LIGO, Virgo, and KAGRA third observation run to test the spatial distribution of these sources. We find no evidence for anisotropy in their angular distribution. We discuss further applications of this method to investigate other gravitational-wave source populations and their correlations to the cosmological large-scale structure.

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Y. Zheng, N. Kouvatsos, J. Golomb, et. al.
Fri, 5 May 23
47/67

Comments: 6 pages, 5 figures

Dissipative Emergence of Inflation from Quasi-Cyclic Universe [CL]

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http://arxiv.org/abs/2305.02367


Inflationary models, especially those with plateau-type potentials, are consistent with the cosmological data, but inflation itself does not resolve the initial singularity. This singularity is resolved, for example, by the idea of the quantum creation of the Universe from nothing such as the tunneling and no-boundary proposals. The simplest one predicts a closed Universe. Motivated by these facts, we investigate the classical dynamics of a closed Universe with a plateau-type potential. Depending on the initial inflaton field value, the Universe can undergo a variety of events: an immediate Big Crunch, a bounce or cyclic phase, and inflation. Although the non-inflationary solutions may appear irrelevant to our Universe, they can be turned into a single or multiple bounces followed by inflation, taking into account the interactions necessary for the reheating of the Universe after inflation. Thus, the dissipative mechanism in our setup explains both the graceful entry to and exit from inflation and gives us an indirect observational handle on the Universe just after creation. We also comment on the implications of these solutions on the probabilistic interpretations of the wave function of the Universe.

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H. Matsui, A. Papageorgiou, F. Takahashi, et. al.
Fri, 5 May 23
49/67

Comments: 53 pages, 11 figures

A trium test on beyond $Λ$CDM triggering parameters [CEA]

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http://arxiv.org/abs/2305.02817


We performed a Bayesian study on the three modified gravity phenomenological parameters, the growth index $\gamma$, the dark energy equation of state parameter $w$ and the lensing deviation from the GR prediction parameter $\Sigma$, using the latest cosmological geometric, growth and lensing probes; all in a consistent implementation within the modified gravity cosmological solver code MGCLASS. We find, when we combine all our probes, i.e. CMB + BAO + $f\sigma_8$ + 3$\times$2pt clustering and lensing probes, assuming flat space, constraints still compatible with general relativity and $\Lambda$CDM with $\omega = -1.025\pm0.045$, $\gamma = 0.633\pm0.044$ and $\Sigma = 0.992\pm0.022$ at 68% level when the latter is considered as constant; and $\gamma_\ell = -0.025 \pm0.045$ when the lensing parameter is parameterized as function of the lensing index, introduced for the first time in this work, as $\Sigma(z)=\Omega_m(z)^{\gamma_\ell}$.

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Z. Sakr
Fri, 5 May 23
62/67

Comments: Originally started as an invited planery talk at EREP 2022

de Sitter Space Decay and Cosmological Constant Relaxation in Braney Unimodular Gravity [CL]

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http://arxiv.org/abs/2305.02349


General covariant unimodular gravity frameworks, based on the Henneaux-Teitelboim formulation, are, in disguise, precisely $4$-form field theories corrected with higher dimension operators. In the presence of charged tensional membranes, any de Sitter space in all such theories is unstable and decays. If the fluxes sourced by membranes are mutually incommensurate, de Sitter geometries comprise a very refined discretuum of states. Whenever the $4$-form sector is dominated by terms linear in flux the almost-Minkowski space is the unique long-time attractor. As a result, a tiny cosmological constant is natural in all such frameworks, without appealing to anthropic reasoning.

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N. Kaloper
Fri, 5 May 23
67/67

Comments: 28 pages, 5 figures

Lorentzian quantum cosmology with torsion [CL]

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http://arxiv.org/abs/2305.01690


We evaluate the Lorentzian gravitational path integral in the presence of non-vanishing torsion with the application of the Picard-Lefschetz theory for minisuperspaces corresponding to a number of phenomenological bouncing cosmological models as well as for the inflationary paradigm. It turns out that the semi-classical wave function derived from the saddle points of the path integral formalism coincides with the solutions of the Wheeler-DeWitt equation. Intriguingly, our analysis showed that the relative probability, derived using these semi-classical wave functions favors universes with smaller values of torsion. Moreover, we find that in the inflationary case, non-zero values of a certain parity-violating component of the torsion enhance the power in the large physical length scales, which can have important observational implications. On the other hand, in the case of bouncing models, the power spectrum is characterized by an initial region of growth, an intermediate oscillatory region, and then again a final region of growth. The shape of the power spectrum in the initial and intermediate regions is sensitive to the abundance of the bounce-enabling matter and torsion, along with the initial wave function of the universe, while the final size modifies the behavior of the power spectrum in the smaller length scales.

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V. Mondal and S. Chakraborty
Thu, 4 May 23
4/60

Comments: N/A

Asymptotic behavior of null geodesics near future null infinity IV: Null-access theorem for generic asymptotically flat spacetime [CL]

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http://arxiv.org/abs/2305.01767


In our previous papers [arXiv:2106.03150, arXiv:2110.10917, arXiv:2208.00822], we analyzed the asymptotic behavior of future directed null geodesics near future null infinity and then we showed a proposition on the accessibility of the null geodesics to future null infinity in a specific class of asymptotically flat spacetimes. In this paper, we adopt the retarded time of the Bondi coordinate as the parameter for the null geodesics and then see that one can relax the assumptions imposed in our previous studies. As a consequence, we obtain a new null-access theorem for generic asymptotically flat spacetimes.

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M. Amo, K. Izumi, Y. Tomikawa, et. al.
Thu, 4 May 23
17/60

Comments: 16 pages, no figures

Machine Learning and Structure Formation in Modified Gravity [CEA]

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http://arxiv.org/abs/2305.02122


In General Relativity approximations based on the spherical collapse model such as Press–Schechter theory and its extensions are able to predict the number of objects of a certain mass in a given volume. In this paper we use a machine learning algorithm to test whether such approximations hold in screened modified gravity theories. To this end, we train random forest classifiers on data from N-body simulations to study the formation of structures in $\Lambda$CDM as well as screened modified gravity theories, in particular $f(R)$ and nDGP gravity. The models are taught to distinguish structure membership in the final conditions from spherical aggregations of density field behaviour in the initial conditions. We examine the differences between machine learning models that have learned structure formation from each gravity, as well as the model that has learned from $\Lambda$CDM. We also test the generalisability of the $\Lambda$CDM model on data from $f(R)$ and nDGP gravities of varying strengths, and therefore the generalisability of Extended-Press-Schechter spherical collapse to these types of modified gravity.

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J. Betts, C. Bruck, C. Arnold, et. al.
Thu, 4 May 23
21/60

Comments: 8 pages, 6 figures

Methods and prospects for gravitational wave searches targeting ultralight vector boson clouds around known black holes [CL]

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http://arxiv.org/abs/2305.00401


Ultralight bosons are predicted in many extensions to the Standard Model and are popular dark matter candidates. The black hole superradiance mechanism allows for these particles to be probed using only their gravitational interaction. In this scenario, an ultralight boson cloud may form spontaneously around a spinning black hole and extract a non-negligible fraction of the black hole’s mass. These oscillating clouds produce quasi-monochromatic, long-duration gravitational waves that may be detectable by ground-based or space-based gravitational wave detectors. We discuss the capability of a new long-duration signal tracking method, based on a hidden Markov model, to detect gravitational wave signals generated by ultralight vector boson clouds, including cases where the signal frequency evolution timescale is much shorter than that of a typical continuous wave signal. We quantify the detection horizon distances for vector boson clouds with current- and next-generation ground-based detectors. We demonstrate that vector clouds hosted by black holes with mass $\gtrsim 60 M_{\odot}$ and spin $\gtrsim 0.6$ are within the reach of current-generation detectors up to a luminosity distance of $\sim 1$ Gpc. This search method enables one to target vector boson clouds around remnant black holes from compact binary mergers detected by gravitational-wave detectors. We discuss the impact of the sky localization of the merger events and demonstrate that a typical remnant black hole reasonably well-localized by the current generation detector network is accessible in a follow-up search.

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D. Jones, L. Sun, N. Siemonsen, et. al.
Thu, 4 May 23
27/60

Comments: 20 pages, 12 figures

Detecting High-Frequency Gravitational Waves in Planetary Magnetosphere [CL]

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http://arxiv.org/abs/2305.01832


High-frequency gravitational waves (HFGWs) carry a wealth of information on the early Universe with a tiny comoving Hubble horizon and astronomical objects of small scale but with dense energy. We demonstrate that the nearby planets, such as Earth and Jupiter, can be utilized as a laboratory for detecting the HFGWs. These GWs are then expected to convert to signal photons in the planetary magnetosphere, across the frequency band of astronomical observation. As a proof of concept, we present the first limits from the existing low-Earth-orbit satellite for specific frequency bands and project the sensitivities for the future more-dedicated detections. The first limits from Juno, the latest mission orbiting Jupiter, are also presented. Attributed to the long path of effective GW-photon conversion and the wide angular distribution of signal flux, we find that these limits are highly encouraging, for a broad range of frequencies including a large portion unexplored before.

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T. Liu, J. Ren and C. Zhang
Thu, 4 May 23
57/60

Comments: 11 pages, 8 figures

Impacts of dark matter interaction on nuclear and neutron star matter within the relativistic mean-field model [CL]

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http://arxiv.org/abs/2305.02065


This thesis explores the effects of dark matter (DM) on neutron stars (NSs) using the relativistic mean-field (RMF) model. The effects of DM on NS properties, including the mass-radius relation, the moment of inertia, and tidal deformability, are calculated by varying its fraction. The study found that the EOS becomes softer with increasing DM momentum, and the DM has marginal effects on nuclear matter properties, except for the EOSs and binding energy per particle. The study also calculated the properties of isolated, static, and rotating DM admixed NS and found that the DM has significant effects on both static and rotating NS. We have also observed that a tiny amount of DM can accumulate inside the NS, and more amount of it makes the NS unstable. The study also suggests that the secondary component might be a NS with DM content if the underlying nuclear EOS is sufficiently stiff. The $f$-mode oscillations of the DM admixed hyperon stars are calculated and found that there exist a correlation between canonical $f$-mode frequency and the dimensionless tidal deformability parameter ($\Lambda_{1.4}$) and we have put a constraint on $f$-mode frequency using GW170817 data. Finally, we have calculated the DM admixed binary NS properties and found that the binary system becomes less deformed and sustains more time in its inspiral phases with the addition of DM. Therefore, we suggest that one can take DM inside the compact objects while modeling the inspiral waveforms for the BNS systems.

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H. Das
Thu, 4 May 23
58/60

Comments: PhD Thesis

Cryogenic payloads for the Einstein Telescope – Baseline design with heat extraction, suspension thermal noise modelling and sensitivity analyses [IMA]

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http://arxiv.org/abs/2305.01419


The Einstein Telescope (ET) is a third generation gravitational wave detector that includes a room-temperature high-frequency (ET-HF) and a cryogenic low-frequency laser interferometer (ET-LF). The cryogenic ET-LF is crucial for exploiting the full scientific potential of ET. We present a new baseline design for the cryogenic payload that is thermally and mechanically consistent and compatible with the design sensitivity curve of ET. The design includes two options for the heat extraction from the marionette, based on a monocrystalline high-conductivity marionette suspension fiber and a thin-wall titanium tube filled with static He-II, respectively. Following a detailed description of the design options and the suspension thermal noise (STN) modelling, we present the sensitivity curves of the two baseline designs, discuss the influence of various design parameters on the sensitivity of ET-LF and conclude with an outlook to future R&D activities.

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X. Koroveshi, L. Busch, E. Majorana, et. al.
Wed, 3 May 23
2/67

Comments: 20 pages, Article to be published/submitted in Physical Review D – Journal

Test of the Second Postulate of Relativity from Gravitational Wave Observations [CL]

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http://arxiv.org/abs/2304.14820


The second postulate of special relativity states that the speed of light in vacuum is independent of the emitter’s motion. Though this claim has been verified in various experiments and observations involving electromagnetic radiation with very high accuracy, such a test for gravitational radiation still needs to be explored. We analyzed data from the LIGO and Virgo detectors to test this postulate for gravitational radiation within the ambit of \textit{emission models}, where the speed of gravitational waves emitted by a source moving with a velocity $v$ relative to a stationary observer is given by ${c’ = c + k\,v}$, where $k$ is a constant. We have estimated the upper bound on the 90\% credible interval over $k$ that parameterizes the deviation from the second postulate to be ${k \leq 8.3 \times {10}^{-18}}$ which is several orders of magnitude more stringent compared to previous bounds obtained from electromagnetic observations. The Bayes’ factor supports the second postulate, with very strong evidence that the data is consistent with the null hypothesis $k = 0$. This confirms that the speed of gravity is independent of the motion of the emitter, upholding the principle of relativity for gravitational interactions.

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R. Ghosh, S. Nair, L. Pathak, et. al.
Wed, 3 May 23
4/67

Comments: 7 pages, 3 figures

Analytical and Numerical Analysis of Circumbinary Disk Dynamics – I: Coplanar Systems [SSA]

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http://arxiv.org/abs/2305.01533


We present an analytical and numerical study of a system composed of a stellar binary pair and a massless, locally isothermal viscous accretion disk that is coplanar to the binary orbital plane. Analytically, we study the effect of the binary’s gravitational potential over short timescales through the study of stability for epicyclic orbits, and over long timescales by revisiting the concept of resonant torques. Numerically, we perform two-dimensional Newtonian numerical simulations of the disk-binary system over a range of binary mass ratios. We find that the results of our simulations are consistent with previous numerical studies. We additionally show, by comparison of the analytical and numerical results, that the circumbinary gap is maintained on the orbital timescale through the driving of epicyclic instabilities, and does not depend on resonant torquing, contrary to standard lore. While our results are applicable to any disk-binary system, we highlight the importance of this result in the search for electromagnetic and gravitational-wave signatures from supermassive black-hole binaries.

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S. Mahesh, S. McWilliams and M. Pirog
Wed, 3 May 23
15/67

Comments: N/A

First test of the consistency relation for the large-scale structure using the anisotropic three-point correlation function of BOSS DR12 galaxies (An explanatory video is available at https://youtu.be/Zi36ooLPhss.) [CEA]

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http://arxiv.org/abs/2305.01142


We present, for the first time, an observational test of the consistency relation for the large-scale structure (LSS) of the Universe through a joint analysis of the anisotropic two- and three-point correlation functions (2PCF and 3PCF) of galaxies. We parameterise the breakdown of the LSS consistency relation in the squeezed limit by $E_{\rm s}$, which represents the ratio of the coefficients of the shift terms in the second-order density and velocity fluctuations. $E_{\rm s}\neq1$ is a sufficient condition under which the LSS consistency relation is violated. A novel aspect of this work is that we constrain $E_{\rm s}$ by obtaining information about the nonlinear velocity field from the quadrupole component of the 3PCF without taking the squeezed limit. Using the galaxy catalogues in the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12, we obtain $E_{\rm s} = -0.92_{-3.26}^{+3.13}$, indicating that there is no violation of the LSS consistency relation in our analysis within the statistical errors. Our parameterisation is general enough that our constraint can be applied to a wide range of theories, such as multicomponent fluids, modified gravity theories, and their associated galaxy bias effects. Our analysis opens a new observational window to test the fundamental physics using the anisotropic higher-order correlation functions of galaxy clustering.

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N. Sugiyama, D. Yamauchi, T. Kobayashi, et. al.
Wed, 3 May 23
17/67

Comments: 17 pages, 6 figures. Explanatory videos are available in several languages: this https URL (English), this https URL (French), this https URL (Spanish), this https URL (German), this https URL (Chinese), and this https URL (English with my voice)

Analytic distribution of the optimal cross-correlation statistic for stochastic gravitational-wave-background searches using pulsar timing arrays [CL]

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http://arxiv.org/abs/2305.01116


We show via both analytical calculation and numerical simulation that the optimal cross-correlation statistic (OS) for stochastic gravitational-wave-background (GWB) searches using data from pulsar timing arrays follows a generalized chi-squared (GX2) distribution-i.e., a linear combination of chi-squared distributions with coefficients given by the eigenvalues of the quadratic form defining the statistic. This observation is particularly important for calculating the frequentist statistical significance of a possible GWB detection, which depends on the exact form of the distribution of the OS signal-to-noise ratio (S/N) $\hat\rho \equiv \hat A_{\rm gw}^2/\sigma_0$ in the absence of GW-induced cross correlations (i.e., the null distribution). Previous discussions of the OS have incorrectly assumed that the analytic null distribution of $\hat\rho$ is well-approximated by a zero-mean unit-variance Gaussian distribution. Empirical calculations show that the null distribution of $\hat\rho$ has “tails” which differ significantly from those for a Gaussian distribution, but which follow (exactly) a GX2 distribution. So, a correct analytical assessment of the statistical significance of a potential detection requires the use of a GX2 distribution.

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J. Hazboun, P. Meyers, J. Romano, et. al.
Wed, 3 May 23
26/67

Comments: 13 pages, 3 Figures

Constraining the ellipticity and frequency of binary neutron star remnant via its gravitational-wave and electromagnetic radiations [HEAP]

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http://arxiv.org/abs/2305.01364


The nature of the merger remnant of binary neutron star (BNS) remains an open question. From the theoretical point of view, one possible outcome is a supra-massive neutron star (SMNS), which is supported by rigid rotation and through its survival of hundreds of seconds before collapsing into a black hole (BH). If this is the case, the SMNS can emit continuous gravitational waves (GW) and electromagnetic (EM) radiation, particularly in the X-ray band. In this work, the ellipticity and initial frequency of SMNS are constrained with a Bayesian framework using simulated X-ray and GW signals, which could be detected by The Transient High Energy Sky and Early Universe Surveyor (THESEUS) and Einstein Telescope (ET), respectively. We found that only considering the X-ray emission can not completely constrain the initial frequency and ellipticity of the SMNS, but it can reduce the ranges of the parameters. Afterwards, we can use the posterior distribution of the X-ray parameter estimates as a prior for the GW parameter estimates. It was found that the 95$\%$ credible region of the joint X-ray-GW analysis was about $10^5$ times smaller than that of the X-ray analysis alone.

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Y. Yuan, X. Fan and H. Lv
Wed, 3 May 23
32/67

Comments: Accepted by MNRAS

Influence of the deviation of the matter power spectrum at small scales on the global 21-cm signal at cosmic dawn [CEA]

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http://arxiv.org/abs/2305.01149


The matter power spectrum has been strongly constrained by astronomical measurements at large scales, but only weakly at small scales. Compared with the standard scenario, the deviation of the matter power spectrum at small scales has influence on the cosmological structure formation, e.g., the comoving number density of dark matter halos. The thermal history of the intergalactic medium (IGM) can be changed if dark matter is made of weakly interacting massive particles and can annihilate into standard model particles. The changes of the evolution of IGM could leave imprints on the relevant astronomical observations. Taking into account the dark matter annihilation, we investigate the impact of the deviation of matter power spectrum at small scales on the global 21-cm signal. In view of the measurements of the global 21-cm signal by the EDGES experiment, we explore the allowed parameter space of $m_s$, which describes the degree of deviation, by requiring the differential brightness temperature of the global 21-cm signal $\delta T_{21} \le -50~\rm mK$ at redshift $z=17$.

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Y. Yang, X. Li and G. Li
Wed, 3 May 23
37/67

Comments: 9 npages, 4 figures. comments welcome

Cosmic acceleration in entropic cosmology [CL]

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http://arxiv.org/abs/2305.01607


In this paper we study the viability of an entropic cosmological model. The effects of entropic gravity are derived from a modified entropy-area relationship with a volumetric entropy term. This model describes a late time limit {cosmic acceleration}, whose origin is related to a volumetric term in the entropy. Moreover, we analyze the phenomenological implications of the entropic model using the Supernovae {\it Pantheon} compilation and the observational Hubble parameter data to find consistency with cosmological observations. Finally, we show the equivalence between the entropic model and a brane world cosmological model, by means of an effective geometrical construction.

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J. Chagoya, I. Díaz-Saldaña, J. López-Domínguez, et. al.
Wed, 3 May 23
52/67

Comments: 10 pages, 3 figures

Loop Corrections in Gravitational Wave Spectrum in Single Field Inflation [CEA]

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http://arxiv.org/abs/2305.01527


We study the one-loop corrections in power spectrum of long gravitational waves induced from small scale modes in the models of single field inflation undergoing a phase of ultra-slow-roll (USR). We show that the spectrum of long tensor perturbations are largely unaffected by the loop corrections from the short scalar modes. In particular, the spectrum of long tensor perturbations is insensitive to the sharpness of the transition from the USR phase to the final slow-roll phase. This is in contrast to the case of scalar power spectrum in which the loop corrections can be large for a sharp transition while it is slow-roll suppressed in a mild transition. We study the tensor-scalar-scalar bispectrum in the squeezed limit and demonstrate that the Maldacena consistency condition does hold.

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H. Firouzjahi
Wed, 3 May 23
54/67

Comments: 19 pages, 1 figure

Ameliorating the Courant-Friedrichs-Lewy condition in spherical coordinates: A double FFT filter method for general relativistic MHD in dynamical spacetimes [CL]

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http://arxiv.org/abs/2305.01537


Numerical simulations of merging compact objects and their remnants form the theoretical foundation for gravitational wave and multi-messenger astronomy. While Cartesian-coordinate-based adaptive mesh refinement is commonly used for simulations, spherical-like coordinates are more suitable for nearly spherical remnants and azimuthal flows due to lower numerical dissipation in the evolution of fluid angular momentum, as well as requiring fewer numbers of computational cells. However, the use of spherical coordinates to numerically solve hyperbolic partial differential equations can result in severe Courant-Friedrichs-Lewy (CFL) stability condition timestep limitations, which can make simulations prohibitively expensive. This paper addresses this issue for the numerical solution of coupled spacetime and general relativistic magnetohydrodynamics evolutions by introducing a double FFT filter and implementing it within the fully MPI-parallelized SphericalNR framework in the Einstein Toolkit. We demonstrate the effectiveness and robustness of the filtering algorithm by applying it to a number of challenging code tests, and show that it passes these tests effectively, demonstrating convergence while also increasing the
timestep significantly compared to unfiltered simulations.

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L. Ji, V. Mewes, Y. Zlochower, et. al.
Wed, 3 May 23
55/67

Comments: 15 pages, 13 figures, revtex4-1

Fundamental cosmology from ANDES precision spectroscopy [IMA]

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http://arxiv.org/abs/2305.01446


Fundamental cosmology observations, such as the detection of the redshift drift and tests of the universality of physical laws, are key science and design drivers of the ArmazoNes high Dispersion Echelle Spectrograph (ANDES), an Extremely Large Telescope instrument. While separate forecasts for each of them have been reported, we have developed Fisher Matrix based forecast tools combining both of these observables. We demonstrate the synergies between the two ANDES datasets, quantifying the improvements in cosmology and fundamental physics parameter constraints for two separate theoretical paradigms. We publicly release this forecast code, which is one of the tools for the optimisation of the ANDES observing strategy.

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C. Marques, C. Martins and C. Alves
Wed, 3 May 23
60/67

Comments: 8 pages, 3 figures, 2 tables, MNRAS (in press)

Generalizations of Quasilinear MOND (QUMOND) [GA]

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http://arxiv.org/abs/2305.01589


I present a class of theories that generalize quasilinear MOND (QUMOND). Like QUMOND, these GQUMOND theories require solving only the linear Poisson equation (twice). Unlike QUMOND, their Lagrangian depends on higher derivatives of the Newtonian potential. They thus dictate different “phantom” densities as virtual sources in the Poisson equation for the MOND potential. These theories might open new avenues to more fundamental theories, and have much heuristic value. I use them to demonstrate that even within limited classes of modified-gravity formulations of MOND, theories can differ substantially on lower-tier MOND predictions. Such GQUMOND theories force, generically, the introduction of dimensioned constants other than the MOND acceleration, $a_0$, such as a length, a frequency, etc. As a result, some of these theories reduce to QUMOND itself only, e.g., on length scales (or, in other versions, dynamical times) larger than some critical value. But in smaller systems (or, alternatively, in ones with shorter dynamical times), MOND effects are screened, even if their internal accelerations are smaller than $a_0$. In such theories it is possible that MOND (expressed as QUMOND) applies on galactic scales, but its departures from Newtonian dynamics are substantially suppressed in some subgalactic systems — such as binary stars, and open, or globular star clusters. The same holds for the effect of the galactic field on dynamics in the inner solar system, which can be greatly suppressed compared with what QUMOND predicts. Tidal effects of a galaxy on smaller subsystems are the same as in QUMOND, for the examples I consider. I also describe briefly versions that do not involve dimensioned constants other than $a_0$, and yet differ from QUMOND in important ways.

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M. Milgrom
Wed, 3 May 23
61/67

Comments: 12 pages

Primordial black holes formation in a early matter dominated era from the pre-big bang scenario [CL]

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http://arxiv.org/abs/2305.01430


We discuss the production of primordial black holes in an early matter dominated era, which typically takes place in string inspired early universe cosmological models. In particular, we consider a pre-big bang scenario (extending previous results regarding formation in the radiation dominated era) where the enhancement of curvature perturbations is induced by a variation of the sound-speed parameter c_s during the string phase of high-curvature inflation. After imposing all relevant observational constraints, we find that the considered class of models is compatible with the production of a large amount of primordial black holes, in the mass range relevant to dark matter, only for a small range of the parameters space. On the other hand, we find that a huge production of light primordial black holes may occur both in such matter dominated era and in the radiation dominated one.

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C. P. and M. G
Wed, 3 May 23
64/67

Comments: 7 pages, 3 figures

GW_CLASS: Cosmological Gravitational Wave Background in the Cosmic Linear Anisotropy Solving System [CL]

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http://arxiv.org/abs/2305.01602


The anisotropies of the Cosmological Gravitational Wave Background (CGWB) retain information about the primordial mechanisms that source the gravitational waves and about the geometry and the particle content of the universe at early times. In this work, we discuss in detail the computation of the angular power spectra of CGWB anisotropies and of their cross correlation with Cosmic Microwave Background (CMB) anisotropies, assuming different processes for the generation of these primordial signals. We present an efficient implementation of our results in a modified version of CLASS which will be publicly available. By combining our new code GW_CLASS with MontePython, we forecast the combined sensitivity of future gravitational wave interferometers and CMB experiments to the cosmological parameters that characterize the cosmological gravitational wave background.

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F. Schulze, L. Dall’Armi, J. Lesgourgues, et. al.
Wed, 3 May 23
65/67

Comments: 63 pages, 16 figures

Observable Gravitational Waves from Hyperkination in Palatini Gravity and Beyond [CL]

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http://arxiv.org/abs/2305.01399


We consider cosmology with an inflaton scalar field with an additional quartic kinetic term. Such a theory can be motivated by Palatini $R+R^2$ modified gravity. Assuming a runaway inflaton potential, we take the Universe to become dominated by the kinetic energy density of the scalar field after inflation. Initially, the leading kinetic term is quartic and we call the corresponding period hyperkination. Subsequently, the usual quadratic kinetic term takes over and we have regular kination, until reheating. We study, both analytically and numerically, the spectrum of primordial gravitational waves generated during inflation and re-entering the horizon during the subsequent eras. We demonstrate that the spectrum is flat for modes re-entering during radiation domination and hyperkination and linear in frequency for modes re-entering during kination: kinetic domination boosts the spectrum, but hyperkination truncates its peak. As a result, the effects of the kinetic period can be extended to observable frequencies without generating excessive gravitational waves, which could otherwise destabilise the process of Big Bang Nucleosynthesis. We show that there is ample parameter space for the primordial gravitational waves to be observable in the near future. If observed, the amplitude and `knee’ of the spectrum will provide valuable insights into the background theory.

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S. López, K. Dimopoulos, A. Karam, et. al.
Wed, 3 May 23
66/67

Comments: 40 pages, 7 figures

Hydrodynamic sound shell model [CL]

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http://arxiv.org/abs/2305.00074


For a cosmological first-order phase transition in the early Universe, the associated stochastic gravitational wave background is usually dominated by sound waves from plasma fluid motions, which have been analytically modeled as a random superposition of freely propagating sound shells but with the force by the scalar field that produces the self-similar profile removed. In this Letter, we propose a new analytic sound shell model by focusing on the forced propagating contribution from the initial collision stage of sound shells when their self-similar profiles are still maintained by the moving bubble walls. We reproduce the causal $k^3$-scaling in the infrared consistent with numerical simulations, and also recover the broad dome in the power spectrum first observed in numerical simulations. The total sound waves should contain both contributions from forced collisions and free propagation of sound shells at early and late stages of the phase transition, respectively.

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R. Cai, S. Wang and Z. Yuwen
Tue, 2 May 23
7/57

Comments: 5 pages (3 figures) + 1 appendix (5 figures)

The Hawking Energy in a Perturbed Friedmann-Lemaître Universe [CL]

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http://arxiv.org/abs/2305.00711


Hawking’s quasi-local energy definition quantifies the energy enclosed by a spacelike 2-sphere in terms of the amount of lightbending on the sphere caused by the energy distribution inside the sphere. This paper establishes for the first time a direct connection between the formal mathematical definition of a quasi-local energy and observations, in the context of cosmological perturbation theory. This is achieved by studying the Hawking Energy of spherical sections of the past lightcone of a cosmic observer in a perturbed Friedmann-Lema\^{i}tre spacetime. We express the Hawking Energy in terms of gauge-invariant perturbation variables and comment on the cosmic observables needed to in principle measure it. We then calculate its angular power spectrum and interpret its contributions.

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D. Stock, E. Dio and R. Durrer
Tue, 2 May 23
17/57

Comments: comments welcome; additional Mathematica file attached

A data science platform to enable time-domain astronomy [IMA]

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http://arxiv.org/abs/2305.00108


SkyPortal is an open-source platform designed to efficiently discover interesting transients, manage follow-up, perform characterization, and visualize the results, all in one application. By enabling fast access to archival and catalog data, cross-matching heterogeneous data streams, and the triggering and monitoring of on-demand observations for further characterization, SkyPortal has been operating at scale for > 2 yr for the Zwicky Transient Facility Phase II community, with hundreds of users, containing tens of millions of time-domain sources, interacting with dozens of telescopes, and enabling community reporting. While SkyPortal emphasizes rich user experiences (UX) across common frontend workflows, recognizing that scientific inquiry is increasingly performed programmatically, SkyPortal also surfaces an extensive and well-documented API system. From backend and frontend software to data science analysis tools and visualization frameworks, the SkyPortal design emphasizes the re-use and leveraging of best-in-class approaches, with a strong extensibility ethos. For instance, SkyPortal now leverages ChatGPT large-language models (LLMs) to automatically generate and surface source-level human-readable summaries. With the imminent re-start of the next-generation of gravitational wave detectors, SkyPortal now also includes dedicated multi-messenger features addressing the requirements of rapid multi-messenger follow-up: multi-telescope management, team/group organizing interfaces, and cross-matching of multi-messenger data streams with time-domain optical surveys, with interfaces sufficiently intuitive for the newcomers to the field. (abridged)

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M. Coughlin, J. Bloom, G. Nir, et. al.
Tue, 2 May 23
19/57

Comments: N/A

A Unified $p_\mathrm{astro}$ for Gravitational Waves: Consistently Combining Information from Multiple Search Pipelines [IMA]

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http://arxiv.org/abs/2305.00071


Recent gravitational-wave transient catalogs have used $p_\mathrm{astro}$, the probability that a gravitational-wave candidate is astrophysical, to select interesting candidates for further analysis. Unlike false alarm rates, which exclusively capture the statistics of the instrumental noise triggers, $p_\mathrm{astro}$ incorporates the rate at which triggers are generated by both astrophysical signals and instrumental noise in estimating the probability that a candidate is astrophysical. Multiple search pipelines can independently calculate $p_\mathrm{astro}$, each employing a specific data reduction. While the range of $p_\mathrm{astro}$ results can help indicate the range of uncertainties in its calculation, it complicates interpretation and subsequent analyses. We develop a statistical formalism to calculate a $\textit{unified } p_\mathrm{astro}$ for gravitational-wave candidates, consistently accounting for triggers from all pipelines, thereby incorporating extra information about a signal that is not available with any one single pipeline. We demonstrate the properties of this method using a toy model and by application to the publicly available list of gravitational-wave candidates from the first half of the third LIGO–Virgo–KAGRA observing run. Adopting a unified $p_\mathrm{astro}$ for future catalogs would provide a simple and easy-to-interpret selection criterion that incorporates a more complete understanding of the strengths of the different search pipelines

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S. Banagiri, C. Berry, G. Davies, et. al.
Tue, 2 May 23
23/57

Comments: 18 pages, 5 figures, 1 table

Observational constraints on power law Starobinsky inflation [CEA]

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http://arxiv.org/abs/2305.00682


In this work we revisit power law, $\frac{1}{M^2}R^\beta$, inflation to find the deviations from $R^2$ inflation allowed by current CMB and LSS observations. We compute the power spectra for scalar and tensor perturbations numerically and perform MCMC analysis to put constraints on parameters $M$ and $\beta$ from Planck-2018, BICEP3 and other LSS observations. We consider general reheating scenario and also vary the number of e-foldings during inflation, $N_{pivot}$, along with the other parameters. We find $\beta = 1.966^{+0.035}{-0.042}$, $M= \left(3.31^{+5}{-2}\right)\times 10^{-5}$ and $N_{pivot} = 41^{+10}_{-10}$ with $95\%\, C.\, L.$. This indicates that the current observations allow deviation from Starobinsky inflation. The scalar spectral index, $n_s$, and tensor-to-scalar ratio, $r$, derived from these parameters, are consistent with the Planck and BICEP3 observations.

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S. Saini and A. Nautiyal
Tue, 2 May 23
34/57

Comments: 13 pages, 5 figures

Novel high-frequency gravitational waves detection with split cavity [CL]

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http://arxiv.org/abs/2305.00877


Gravitational waves can generate electromagnetic effects inside a strong electric or magnetic field within the Standard Model and general relativity. Here we propose using a quarterly split cavity and LC-resonance circuit to detect a high-frequency gravitational wave from 0.1 MHz to GHz. We perform a full 3D simulation of the cavity’s signal for sensitivity estimate. Our sensitivity depends on the coherence time scale of the high-frequency gravitational wave sources and the volume size of the split cavity. We discuss the resonant measurement schemes for narrow-band gravitational wave sources and also a non-resonance scheme for broadband signals. For a meter-sized split cavity under a 14 Tesla magnetic field, the LC resonance enhanced sensitivity to the gravitational wave strain is expected to reach $h\sim 10^{-20}$ around $10$ MHz.

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C. Gao, Y. Gao, Y. Liu, et. al.
Tue, 2 May 23
50/57

Comments: 8 pages, 7 figures

Constraining the quintessential \texorpdfstring{$α$}{a}-attractor inflation through dynamical horizon exit method [CL]

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http://arxiv.org/abs/2305.00230


In the present paper, we perform a sub-Planckian quantum mode analysis of linear cosmological perturbation in the inflaton field over a classical quasi de-Siter metric background by dynamical horizon exit (DHE) method. In this way, we probe the inflationary regime of a quintessential $\alpha$-attractor model by analysing the COBE/Planck normalized power spectra, spectral indices, tensor to scalar ratio, number of e-folds, running of the spectral index and inflationary Hubble parameter in $k$-space. We compare our results with ordinary $\alpha$-attractor $E$ and $T$ models and with that of Planck-2018 results. Our estimated values of $n_s$ and $r$ lie within $68\%$ CL with respect to Planck data for $k=0.001 – 0.009$ Mpc$^{-1}$ for all values of $\alpha$. The $\alpha$ values, obtained in our calculations satisfy various post inflationary constraints regarding preheating and reheating, reported in current literature. We observe that quintessence sets an upper bound of $\alpha=4.3$ and thereby restricts the model from becoming of the power law type, making it more efficacious than ordinary $\alpha$-attractors in explaining both inflation and dark energy. A striking observation in our analyses is that, unlike in our previous study, we find a continuous values of $\alpha$ within $\frac{1}{10}\leq \alpha\leq 4.3$ for the specified $k$ range. At the end, we have shown that the model parameters constrained in this work give a very small vacuum density $\sim 10^{-117}-10^{-115} M_P^4$ which is an essential criterion for current and future dark energy observations of the universe.

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A. Sarkar and B. Ghosh
Tue, 2 May 23
52/57

Comments: 46 pages, 20 figures, 2 tables

Limitations in Testing the Lense-Thirring Effect with LAGEOS and the Newly Launched Geodetic Satellite LARES 2 [CL]

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http://arxiv.org/abs/2304.14649


The new geodetic satellite LARES 2, cousin of LAGEOS and sharing with it almost the same orbital parameters apart from the inclination, displaced by 180 deg, was launched last year. Its proponents suggest using the sum of the nodes of LAGEOS and of LARES 2 to measure the sum of the Lense-Thirring node precessions independently of the systematic bias caused by the even zonal harmonics of the geopotential, claiming a final $\simeq 0.2$ percent total accuracy. In fact, the actual orbital configurations of the two satellites do not allow one to attain the sought for mutual cancellation of their classical node precessions due to the Earth’s quadrupole mass moment, as their sum is still $\simeq 5000$ times larger than the added general relativistic rates. This has important consequences. One is that the current uncertainties in the eccentricities and the inclinations of both satellites do not presently allow the stated accuracy goal to be met, needing improvements of 3-4 orders of magnitude. Furthermore, the imperfect knowledge of the Earth’s angular momentum $S$ impacts the uncancelled sum of the node precessions, from 150 to 4900 percent of the relativistic signal depending on the uncertainty assumed in $S$. It is finally remarked that the real breakthrough in reliably testing the gravitomagnetic field of the Earth would consist in modeling it and simultaneously estimating one or more dedicated parameter(s) along with other ones characterising the geopotential, as is customarily performed for any other dynamical feature.

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L. Iorio
Mon, 1 May 23
15/51

Comments: LaTex2e, 17 pages, no figures, no tables

Scalar polarization window in gravitational-wave signals [CL]

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http://arxiv.org/abs/2304.14430


Scalar polarization modes of gravitational waves, which are often introduced in the context of the viable extension of gravity, have been actively searched. However, couplings of the scalar modes to the matter are strongly constrained by the fifth-force experiments. Thus, the amplitude of scalar polarization in the observed gravitational-wave signal must be significantly suppressed compared to that of the tensor modes. Here, we discuss the implications of the experiments in the solar system on the detectability of scalar modes in gravitational waves from compact binary coalescences, taking into account the whole processes from the generation to the observation of gravitational waves. We first claim that the energy carried by the scalar modes at the generation is, at most, that of the tensor modes from the observed phase evolution of the inspiral gravitational waves. Next, we formulate general gravitational-wave propagation and point out that the energy flux hardly changes through propagation as long as the background changes slowly compared to the wavelength of the propagating waves. Finally, we show that the possible magnitude of scalar polarization modes detected by the ground-based gravitational-wave telescopes is already severely constrained by the existing gravity tests in the solar system.

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H. Takeda, Y. Manita, H. Omiya, et. al.
Mon, 1 May 23
30/51

Comments: 18 pages

Cosmology under the fractional calculus approach: a possible $H_0$ tension resolution? [CL]

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http://arxiv.org/abs/2304.14465


Recently, a new field of study called fractional cosmology has emerged. It uses fractional calculus to modify the standard derivative equations and change the Friedmann equations. The evolution of cosmic species densities is also affected by the $\mu$ fractional parameter and the age of the Universe $t_0$. This new approach to cosmology modifies the Friedmann equations and allows for a late cosmic acceleration without the need for a dark energy component. This could be a breakthrough in solving longstanding problems in cosmology. By analyzing observational Hubble data and Type Ia supernovae, we have been able to place strict constraints on the fractional and cosmological parameters. Our results suggest that the Universe may be older than previously estimated. We also explore whether fractional cosmology can help resolve the $H_0$ tension.

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G. Leon, M. García-Aspeitia, G. Fernandez-Anaya, et. al.
Mon, 1 May 23
36/51

Comments: We have gathered information from arXiv:2207.00878 and arXiv:2303.16409 to create a report on the topic of [gr-qc]. The report focuses on the presentation given by Genly Leon at the Tensions in Cosmology Corfu2022 conference, titled “Cosmology under the fractional calculus approach: a possible $H_0$ tension resolution?” (limit of 15 pages)

Detecting Fundamental Vector Fields with LISA [CL]

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http://arxiv.org/abs/2304.14129


The advent of gravitational wave astronomy has seen a huge influx of new predictions for potential discoveries of beyond the Standard Model fields. The coupling of all fundamental fields to gravity, together with its dominance on large scales, makes gravitational physics a rich laboratory to study fundamental physics. This holds especially true for the search for the elusive dark photon, a promising dark matter candidate. The dark photon is predicted to generate instabilities in a rotating black hole spacetime, birthing a macroscopic Bose-Einstein condensate. These condensates can especially form around super massive black holes, modifying the dynamical inspiralling process. This then opens another window to leverage future space-borne gravitational wave antennas to join the hunt for the elusive dark matter particle. This study builds a preliminary model for the gravitational waveform emitted by such a dressed extreme mass-ratio inspiral. Comparing these waveforms to the vacuum scenario allows projections to the potential constrainability on the dark photon mass by space-borne gravitational wave antennas. The superradiant instability of a massive vector field on a Kerr background is calculated and the modification to the dynamics of an inspiralling solar mass-scale compact object is determined with approximations on the backreaction effect of the cloud on the compact object. The end result is the projection that the LISA mission should be able to constrain the dark photon mass using extreme mass ratio inspirals in the range $[1.8 \times 10^{-17}, 4.47 \times 10^{-16}]$ eV.

Read this paper on arXiv…

S. Fell, L. Heisenberg and D. Veske
Fri, 28 Apr 23
8/68

Comments: 21 Pages, 8 Figures

Multi-field inflation with large scalar fluctuations: non-Gaussianity and perturbativity [CEA]

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http://arxiv.org/abs/2304.14260


Recently multi-field inflation models that can produce large scalar fluctuations on small scales have drawn a lot of attention, primarily because they could lead to primordial black hole production and generation of large second-order gravitational waves. In this work, we focus on models where the scalar fields responsible for inflation live on a hyperbolic field space. In this case, geometrical destabilisation and non-geodesic motion are responsible for the peak in the scalar power spectrum. We present new results for scalar non-Gaussianity and discuss its dependence on the model’s parameters. On scales around the peak, we typically find that the non-Gaussianity is large and close to local in form. We validate our results by employing two different numerical techniques, utilising the transport approach, based on full cosmological perturbation theory, and the $\delta N$ formalism, based on the separate universe approximation. We discuss implications of our results for the perturbativity of the underlying theory, focusing in particular on versions of these models with potentially relevant phenomenology at interferometer scales.

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L. Iacconi and D. Mulryne
Fri, 28 Apr 23
10/68

Comments: 36 pages, 17 figures

Optimal TDI2.0 of sensitive curve for main space GW detector [IMA]

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http://arxiv.org/abs/2304.14027


Time-delay interferometry (TDI) is a crucial technology for space-based gravitational wave detectors. Previous studies have identified the optimal TDI configuration for the first-generation. In this research, we used an Algebraic approach theory to describe the TDI space and employed a method to maximize the signal-to-noise ratio (SNR) to derive the optimal TDI combination for the second-generation. When this combination is used in the sensitivity curve, we observed enhancements of up to 1.91 times in the low-frequency domain and 2 to 3.5 times in the high-frequency domain compared to the Michelson combination. Furthermore, changes in the detector index significantly affect the optimization effect. We also present detection scenarios for several low-frequency gravitational wave sources. Compared to the first-generation TDI optimization, the SNR value for verification double white dwarfs (DWD) and the detection rate for DWD increase by 16.5%.

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Y. Tian and Z. Li
Fri, 28 Apr 23
28/68

Comments: 7 pages,9 figures

Identifying Strongly Lensed Gravitational Waves with the Third-generation Detectors [IMA]

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http://arxiv.org/abs/2304.13967


The joint detection of GW signals by a network of instruments will increase the detecting ability of faint and far GW signals with higher signal-to-noise ratios (SNRs), which could improve the ability of detecting the lensed GWs as well, especially for the 3rd generation detectors, e.g. Einstein Telescope (ET) and Cosmic Explorer (CE). However, identifying Strongly Lensed Gravitational Waves (SLGWs) is still challenging. We focus on the identification ability of 3G detectors in this article. We predict and analyze the SNR distribution of SLGW signals and prove only 50.6\% of SLGW pairs detected by ET alone can be identified by Lens Bayes factor (LBF), which is a popular method at present to identify SLGWs. For SLGW pairs detected by CE\&ET network, owing to the superior spatial resolution, this number rises to 87.3\%. Moreover, we get an approximate analytical relation between SNR and LBF. We give clear SNR limits to identify SLGWs and estimate the expected yearly detection rates of galaxy-scale lensed GWs that can get identified with 3G detector network.

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Z. Gao, K. Liao, L. Yang, et. al.
Fri, 28 Apr 23
47/68

Comments: 9 pages, 7 figures

Perturbative Correction to the Average Expansion Rate of Spacetimes with Perfect Fluids [CL]

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http://arxiv.org/abs/2304.14187


This paper discusses the leading-order correction induced by cosmological perturbations on the average expansion rate of an expanding spacetime, containing one or many perfect fluids. The calculation is carried out up to the second order in the perturbations, and is kept as general as possible. In particular, no approximation such as a long-wavelength or a short-wavelength limit is invoked, and all three types of perturbations (scalar, vector, and tensor) are considered. First, the average value of the expansion rate is computed over a three-dimensional space-like surface where the total density of the fluids is constant. Then, a formula is derived relating that average value to the one over any other surface, on which a different scalar property of the fluids is constant. Moreover, the general formulas giving the correction to the average expansion rate are applied, in particular, to the case of a spacetime containing a single fluid with a constant equation of state. The sign and the effective equation of state of the corresponding back-reaction effect in the first Friedmann equation are examined.

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V. Comeau
Fri, 28 Apr 23
53/68

Comments: N/A

Periodic orbits and their gravitational wave radiations in a polymer black hole in loop quantum gravity [CL]

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http://arxiv.org/abs/2304.14160


This article provides a detailed investigation into the motion of the surrounding particles around a polymer black hole in loop quantum gravity (LQG). Using effective potential, the critical bound orbits and innermost stable circular orbits (ISCO) are analyzed. The study finds that the radii and angular momentum of the critical bound orbits decrease with an increase in the parameter $A_\lambda$ which labels the LQG effects, while the energy and angular momentum of the ISCO also decreases with an increase in $A_\lambda$. Based on these findings, we then explore the periodic orbits of the polymer black hole in LQG using rational numbers composed of three integers. Our results show that the rational numbers increase with the energy of particles and decrease with the increase of angular momentum based on a classification scheme. Moreover, compared to a Schwarzschild black hole, the periodic orbits in a polymer black hole in LQG consistently have lower energy, providing a potential method for distinguishing a polymer black hole in LQG from a Schwarzschild black hole. Finally, we also examine the gravitational wave radiations of the periodic orbits of a test object which orbits a supermassive polymer black hole in LQG, which generates intricate GW waveforms that can aid in exhibiting the gravitational structure of the system.

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Z. Tu, T. Zhu and A. Wang
Fri, 28 Apr 23
54/68

Comments: 14 pages, 10 figures, 2 tables

London-like tensor modes of gravitational waves in cosmic string cosmology [CL]

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http://arxiv.org/abs/2304.14222


From a classical analysis, we show that gravitational waves in a cosmological medium with equation of state $\omega=-1/3$ can follow a London-like equation, implying that some gravitational wave solutions present a decay for certain wavelengths. This scenario, corresponding to a cosmic string cosmology, induces an attenuation temporal scale on the gravitational wave propagation. We discuss on how these solutions impose a limit on the wavelength of the waves that can propagate, which depends on the type of spatial curvature and the energy density content of this type of cosmology.

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C. Aravena-Plaza, V. Muñoz and F. Asenjo
Fri, 28 Apr 23
62/68

Comments: N/A

The integrated perturbation theory for cosmological tensor fields III: Projection effects [CEA]

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http://arxiv.org/abs/2304.13304


The integrated perturbation theory (iPT) is a set of methods in nonlinear perturbation theory for the structure formation in the Universe. In Papers~I and II, the basic formalism and technical methods of the iPT for cosmological tensor fields are developed, generalizing the corresponding theory for scalar fields. In previous papers, methods to predict statistical quantities, such as power spectra, correlation functions, etc., of three-dimensional tensor fields are developed based on the iPT. However, observations of tensors, such as angular momenta and shapes of galaxies, etc., are only possible after the three-dimensional tensors are projected onto the two-dimensional sky. In this paper, power spectra and correlation functions of projected two-dimensional tensors are related to those of original three-dimensional tensors, so that one can make predictions for the observable statistics of projected tensor fields from the iPT. The relations are consistently represented on the basis of irreducible decomposition of both two- and three-dimensional tensors.

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T. Matsubara
Thu, 27 Apr 23
3/78

Comments: 30 pages, no figure, this paper is the third of a series, the first one is arXiv:2210.10435 and the second one is arXiv:2210.11085

The directional isotropy of LIGO-Virgo binaries [CL]

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http://arxiv.org/abs/2304.13254


We demonstrate how to constrain the degree of absolute alignment of the total angular momenta of LIGO-Virgo binary black holes, looking for a special direction in space that would break isotropy. We also allow for inhomogeneities in the distribution of black holes over the sky. Making use of dipolar models for the spatial distribution and orientation of the sources, we analyze 57 signals with false-alarm rates < 1/yr from the third LIGO-Virgo observing run. Accounting for selection biases, we find the population of LIGO-Virgo black holes to be fully consistent with both homogeneity and isotropy. We additionally find the data to constrain some directions of alignment more than others, and produce posteriors for the directions of total angular momentum of all binaries in our set. All code and data are made publicly available in https://github.com/maxisi/gwisotropy/.

Read this paper on arXiv…

M. Isi, W. Farr and V. Varma
Thu, 27 Apr 23
21/78

Comments: N/A

Searching For Stochastic Gravitational Waves Below a Nanohertz [HEAP]

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http://arxiv.org/abs/2304.13042


The stochastic gravitational-wave background is imprinted on the times of arrival of radio pulses from millisecond pulsars. Traditional pulsar timing analyses fit a timing model to each pulsar and search the residuals of the fit for a stationary time correlation. This method breaks down at gravitational-wave frequencies below the inverse observation time of the array; therefore, existing analyses restrict their searches to frequencies above 1 nHz. An effective method to overcome this challenge is to study the correlation of secular drifts of parameters in the pulsar timing model itself. In this paper, we show that timing model correlations are sensitive to sub-nanohertz stochastic gravitational waves and perform a search using existing measurements of binary spin-down rates and pulsar spin-decelerations. We do not observe a signal at our present sensitivity, constraining the stochastic gravitational-wave relic energy density to $\Omega_\text{GW} ( f ) < 3.9 \times 10 ^{ – 9} $ at 450 pHz with sensitivity which scales as the frequency squared until approximately 10 pHz. We place additional limits on the amplitude of a power-law spectrum of $A_\star \lesssim 8\times10^{-15}$ for the spectral index expected from supermassive black hole binaries, $\gamma = 13/3$. If a detection of a supermassive black hole binary signal above 1 nHz is confirmed, this search method will serve as a critical complementary probe of the dynamics of galaxy evolution.

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W. DeRocco and J. Dror
Thu, 27 Apr 23
26/78

Comments: 13 pages, 2 figures

Bouncing and inflationary dynamics in quantum cosmology in the de Broglie-Bohm interpretation [CL]

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http://arxiv.org/abs/2304.13059


The quantum cosmology of the flat Friedmann-Lema{\^i}tre-Robertson-Walker Universe, filled with a scalar field, is considered in the de Broglie-Bohm (dBB) interpretation framework. A stiff-matter quantum bounce solution is obtained. The bouncing and subsequent pre-inflationary and inflationary dynamics are studied in details. We consider some representative primordial inflation models as examples, for which analytical expressions characterizing the dynamical quantities can be explicitly derived. The dependence of the inflationary dynamics on the quantum bounce parameters is then analyzed. The parameters emerging from our description are constrained by requiring the produced dynamics to be in accordance with some key cosmological quantities. The constraining conditions are also illustrated through regions of parameter space in terms of the bounce quantities.

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G. Vicente, R. Ramos and V. Magalhães
Thu, 27 Apr 23
27/78

Comments: 18 pages, 2 figures

Parameter estimation of binary black holes in the endpoint of the up-down instability [CL]

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http://arxiv.org/abs/2304.13063


Black-hole binary spin precession admits equilibrium solutions corresponding to systems with (anti-) aligned spins. Among these, binaries in the up-down configuration, where the spin of the heavier (lighter) black hole is co- (counter-) aligned with the orbital angular momentum, might be unstable to small perturbations of the spin directions. The occurrence of the up-down instability leads to gravitational-wave sources that formed with aligned spins but are detected with precessing spins. We present a Bayesian procedure based on the Savage-Dickey density ratio to test the up-down origin of gravitational-wave events. This is applied to both simulated signals, which indicate that achieving strong evidence is within the reach of current experiments, and the LIGO/Virgo events released to date, which indicate that current data are not informative enough.

Read this paper on arXiv…

V. Renzis, D. Gerosa, M. Mould, et. al.
Thu, 27 Apr 23
32/78

Comments: N/A

Halo Formation from Yukawa Forces in the Very Early Universe [CEA]

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http://arxiv.org/abs/2304.13053


If long-range attractive forces exist and are stronger than gravity then cosmic halo formation can begin in the radiation-dominated era. We study a simple realization of this effect in a system where dark matter fermions have Yukawa interactions mediated by scalar particles, analogous to the Higgs boson in the standard model. We develop a self-consistent description of the system including exact background dynamics of the scalar field, and precise modelling of the fermion density fluctuations. For the latter, we provide accurate approximations for the linear growth as well as quantitative modelling of the nonlinear evolution using N-body simulations. We find that halo formation occurs exponentially fast and on scales substantially larger than simple estimates predict. The final fate of these halos remains uncertain, but could be annihilation, dark stars, primordial black holes, or even the existence of galaxy-sized halos at matter-radiation equality. More generally, our results demonstrate the importance of mapping scalar-mediated interactions onto structure formation outcomes and constraints for beyond the standard model theories.

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G. Domènech, D. Inman, A. Kusenko, et. al.
Thu, 27 Apr 23
36/78

Comments: 22 pages + references, 13 figures

Revisiting compaction functions [CL]

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http://arxiv.org/abs/2304.13284


Shibata and Sasaki (1999) introduced the so-called compaction function. Since then, it has been empirically established that the maximum value of this function (or its volume-averaged counterpart) in the long-wavelength solutions gives a very robust threshold of primordial black hole formation. In this paper, we show that in spite of initial intention, the Shibata-Sasaki compaction function cannot be interpreted as the ratio of the mass excess to the areal radius in the constant-mean-curvature slice of their choice but coincides with that in the {\it comoving} slice up to a constant factor depending on the equation of state. We also discuss the gauge-(in)dependence of the legitimate compaction function, i.e., the ratio of the mass excess to the areal radius, in the long-wavelength solutions.

Read this paper on arXiv…

T. Harada, C. Yoo and Y. Koga
Thu, 27 Apr 23
44/78

Comments: 17 pages

A ring-like accretion structure in M87 connecting its black hole and jet [HEAP]

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http://arxiv.org/abs/2304.13252


The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation^{1,2}. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole^3. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of 8.4_{-1.1}^{+0.5} Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects in addition to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of the jet-launching region is wider than the expected profile of a black-hole-driven jet, suggesting the possible presence of a wind associated with the accretion flow.

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R. Lu, K. Asada, T. Krichbaum, et. al.
Thu, 27 Apr 23
45/78

Comments: 50 pages, 18 figures, 3 tables, author’s version of the paper published in Nature

Preheating in Einstein-Cartan Higgs Inflation: Oscillon formation [CL]

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http://arxiv.org/abs/2304.13056


We make use of classical lattice simulations in 3 + 1 dimensions to study the preheating stage of Higgs Inflation in Einstein-Cartan gravity. Focusing for concreteness on a simplified scenario involving the seminal Nieh-Yan term, we demonstrate the formation of dense and spatially localized oscillon configurations constituting up to 70% of the total energy density. The emergence of these meta-stable objects may lead to a prolonged period of matter domination, effectively modifying the post-inflationary history of the Universe as compared to the metric and Palatini counterparts. Notably, the creation of oscillons comes together with a significant gravitational wave signal, whose typical frequency lies, however, beyond the range accessible by existing and planned gravitational wave experiments. The impact of the Standard Model gauge bosons and fermions and the potential extension of our results to more general Einstein-Cartan settings is also discussed.

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M. Piani and J. Rubio
Thu, 27 Apr 23
56/78

Comments: 28 pages, 9 figures, 1 table. Link for the animation: this https URL

Enhanced Extreme Mass Ratio Inspiral Rates into Intermediate Mass Black Holes [GA]

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http://arxiv.org/abs/2304.13062


Extreme mass ratio inspirals (EMRIs) occur when stellar-mass compact objects begin a gravitational wave (GW) driven inspiral into massive black holes. EMRI waveforms can precisely map the surrounding spacetime, making them a key target for future space-based GW interferometers such as {\it LISA}, but their event rates and parameters are massively uncertain. One of the largest uncertainties is the ratio of true EMRIs (which spend at least thousands of orbits in the {\it LISA} band) and direct plunges, which are in-band for at most a handful of orbits and are not detectable in practice. In this paper, we show that the traditional dichotomy between EMRIs and plunges — EMRIs originate from small semimajor axes, plunges from large — does not hold for intermediate-mass black holes with masses $M_\bullet \lesssim 10^5 M_\odot$. In this low-mass regime, a plunge always has an $\mathcal{O}(1)$ probability of failing and transitioning into a novel “cliffhanger” EMRI. Cliffhanger EMRIs are more easily produced for larger stellar-mass compact objects, and are less likely for smaller ones. This new EMRI production channel can dominate volumetric EMRI rates $\dot{n}{\rm EMRI}$ if intermediate-mass black holes are common in dwarf galactic nuclei, potentially increasing $\dot{n}{\rm EMRI}$ by an order of magnitude.

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I. Qunbar and N. Stone
Thu, 27 Apr 23
61/78

Comments: 8 pages, 6 figures, comments welcome

Bañados-Silk-West effect with finite forces near different types of horizons: general classification of scenarios [CL]

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http://arxiv.org/abs/2304.13087


If two particles move towards a black hole and collide in the vicinity of the horizon, under certain conditions their energy $E_{c.m.}$ in the center of mass frame can grow unbounded. This is the Ba\~{n}ados-Silk-West (BSW) effect. Usually, this effect is considered for extremal horizons and geodesic (or electrogedesic) trajectories. We study this effect in a more general context, when both geometric and dynamic factors are taken into account. We consider generic axially symmetric rotating black holes. The near-horizon behavior of metric coefficients is determined by three numbers $p,~q,$ $k$ that appear in the Taylor expansions for different types of a horizon$.$ This includes nonextremal, extremal and ultraextremal horizons. We also give general classification of possible trajectories that include so-called usual, subcritical, critical and ultracritical ones depending on the near-horizon behavior of the radial component of the four-velocity. We assume that particles move not freely but under the action of some unspecified force. We find when the finiteness of a force and the BSW effect are compatible with each other. The BSW effect implies that one of two particles has fine-tuned parameters. We show that such a particle always requires an infinite proper time for reaching the horizon. Otherwise, either a force becomes infinite or a horizon fails to be regular. This realizes the so-called principle of kinematic censorship that forbids literally infinite $E_{c.m.}$ in any act of collision. The obtained general results are illustrated for the Kerr-Newman-(anti-)de Sitter metric used as an example. The description of diversity of trajectories suggested in our work can be of use also in other contexts, beyond the BSW effect. In particular, we find the relation between a force and the type of a trajectory.

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H. H.V.Ovcharenko and O. O.B.Zaslavskii
Thu, 27 Apr 23
62/78

Comments: 38 pages, 2 figures

Relativistic Corrections in White Dwarf Asteroseismology [SSA]

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http://arxiv.org/abs/2304.13055


With the precision now afforded by modern space-based photometric observations from the retired K2 and current TESS missions, the effects of general relativity (GR) may be detectable in the light curves of pulsating white dwarfs (WDs). Almost all WD models are calculated using a Newtonian description of gravity and hydrodynamics. To determine if inclusion of GR leads to observable effects, we used idealized models of compact stars and made side-by-side comparison of mode periods computed using a (i) Newtonian and (ii) GR description of the equilibrium structure and nonradial pulsations. For application to white dwarfs, it is only necessary to include the first post-Newtonian (1PN) approximation to GR. The mathematical nature of the linear nonradial pulsation problem is then qualitatively unchanged and the GR corrections can be written as extensions of the classic Dziembowski equations. As such, GR effects might easily be included in existing asteroseismology codes. The idealized stellar models are (i) \pn1 relativistic polytropes and (ii) stars with cold degenerate-electron equation of state featuring a near-surface chemical transition from $\mu_e = 2$ to $\mu_e = 1$, simulating a surface hydrogen layer. Comparison of Newtonian and 1PN normal mode periods reveals fractional differences on the order of the surface gravitational redshift $z$. For a typical WD, this fractional difference is $\sim 10^{-4}$ and is greater than the period uncertainty $\sigma_{\Pi}/\Pi$ of many white dwarf pulsation modes observed by TESS. A consistent theoretical modeling of periods observed in these stars should in principle include GR effects to 1PN order.

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S. Boston, C. Evans and J. Clemens
Thu, 27 Apr 23
71/78

Comments: N/A

Stochastic gravitational-wave background at 3G detectors as a smoking gun for microscopic dark matter relics [CEA]

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http://arxiv.org/abs/2304.13576


Microscopic horizonless relics could form in the early universe either directly through gravitational collapse or as stable remnants of the Hawking evaporation of primordial black holes. In both cases they completely or partially evade cosmological constraints arising from Hawking evaporation and in certain mass ranges can explain the entirety of the dark matter. We systematically explore the stochastic gravitational-wave background associated with the formation of microscopic dark-matter relics in various scenarios, adopting an agnostic approach and discussing the limitations introduced by existing constraints, possible ways to circumvent the latter, and expected astrophysical foregrounds. Interestingly, this signal is at most marginally detectable with current interferometers but could be detectable by third-generations instruments such as the Einstein Telescope, strengthening their potential as discovery machines.

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G. Franciolini and P. Pani
Thu, 27 Apr 23
74/78

Comments: 11 pages, 4 figures

Charged particle dynamics in parabolic magnetosphere around Schwarzschild black hole [CL]

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http://arxiv.org/abs/2304.13603


The study of charged particle dynamics in the combined gravitational and magnetic field can provide important theoretical insight into astrophysical processes around black holes. In this paper, we explore the charged particle dynamics in parabolic magnetic field configuration around Schwarzschild black hole, since the paraboloidal shapes of magnetic field lines around black holes are well motivated by the numerical simulations and supported by observations of relativistic jets. Analysing the stability of bounded orbits and using the effective potential approach, we show the possibility of existence of stable circular off-equatorial orbits around the symmetry axis. We also show the influence of radiation reaction force on the dynamics of charged particles, in particular on the chaoticity of the motion and Poincar\'{e} sections, oscillatory frequencies, and emitted electromagnetic spectrum. Applied to Keplerian accretion disks, we show that in parabolic magnetic field configuration, the thin accretion configurations can be either destroyed or transformed into a thick toroidal structure given the radiation reaction and electromagnetic-disk interactions included. Calculating the Fourier spectra for radiating charged particle trajectories, we find that the radiation reaction force does not affect the main frequency peaks, however, it lowers the higher harmonics making the spectrum more flat and diluted in high frequency range.

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M. Kološ, M. Shahzadi and A. Tursunov
Thu, 27 Apr 23
78/78

Comments: 23 pages, 16 figures

Lorentz Violation in Finsler Geometry [CL]

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http://arxiv.org/abs/2304.12767


Lorentz invariance is one of the foundations of modern physics; however, Lorentz violation may happen from the perspective of quantum gravity, and plenty of studies on Lorentz violation have arisen in recent years. As a good tool to explore Lorentz violation, Finsler geometry is a natural and fundamental generalization of Riemann geometry. The Finsler structure depends on both coordinates and velocities. Here, we simply introduce the mathematics of Finsler geometry. We review the connection between modified dispersion relations and Finsler geometries and discuss the physical influence from Finsler geometry. We review the connection between Finsler geometries and theories of Lorentz violation, such as the doubly special relativity, the standard-model extension, and the very special relativity.

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J. Zhu and B. Ma
Wed, 26 Apr 23
30/62

Comments: 29 pages, no figure, final version for journal publication

Constraints on $f(Q)$ logarithmic model using gravitational wave standard sirens [CL]

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http://arxiv.org/abs/2304.12601


In this paper, we revise the constraints on the $f(Q)=Q/(8\pi G) – \alpha \ln(Q/Q_0)$, symmetric teleparallel model using local measurements and gravitational waves mock standard sirens. Using observational local SNIa and BAO data and energy conditions, the logarithmic $f(Q)$ model is capable of explaining the cosmic late-time acceleration by geometrical means. This result suggests that the logarithmic symmetric teleparallel model could be a candidate to solve the cosmological constant problem. In the case of the simulated standard siren data, by using the performance of the future ET and LISA detectors, we expect to be able to measure the current Hubble constant $H_0$, and the matter content $\Omega_m$, with a precision better than 1% and 6%, respectively. Furthermore, we explore the predicted $f(Q)$ logarithmic model deviation from the standard GR using ET and LISA mock standard sirens. The ratio $d_L^{\text{gw}}(z)/d_L^{\text{em}}(z)$, which quantifies the deviation from GR gives us a significant deviation higher than 13% at $z=1$, and it continues growing to reach a deviation higher than 18% in its median value. Future standard siren data will be able to quantify the strength of the deviation from GR and hence whether a cosmology like the one implied by this $f(Q)$ model is feasible.

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J. Nájera, C. Alvarado and C. Escamilla-Rivera
Wed, 26 Apr 23
32/62

Comments: 16 pages, 3 figures

Universal relations to measure neutron star properties from targeted r-mode searches [CL]

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http://arxiv.org/abs/2304.12356


R-mode oscillations of rotating neutron stars(NS) are promising candidates for continuous gravitational wave (GW) observations. In our recent work(Ghosh et al. 2023), we derived universal relations of the NS parameters, compactness and dimensionless tidal deformability with the r-mode frequency. In this work, we investigate how these universal relations can be used to infer various NS intrinsic parameters following a successful detection of the r-modes. In particular, we show that for targeted r-mode searches, these universal relations along with the “I-Love-Q” relation can be used to estimate both the moment of inertia and the distance of the NS thus breaking the degeneracy of distance measurement for continuous gravitational wave(CGW) observations. We also discuss that with a prior knowledge of the distance of the NS from electromagnetic observations, these universal relations can also be used to constrain the dense matter equation of state (EOS) inside NS. We quantify the accuracy to which such measurements can be done using the Fisher information matrix for a broad range of possible, unknown parameters, for both the a-LIGO and Einstein Telescope (ET) sensitivities.

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S. Ghosh
Wed, 26 Apr 23
39/62

Comments: 8 pages, 7 figures, Submitted to MNRAS

Exploring Models of Running Vacuum Energy with Viscous Dark Matter from a Dynamical System Perspective [CL]

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http://arxiv.org/abs/2304.12407


Running vacuum models and viscous dark matter scenarios beyond perfect fluid idealization are two appealing theoretical strategies that have been separately studied as alternatives to solve some problems rooted in the $\Lambda$CDM cosmological model. In this paper, we combine these two notions in a single cosmological setting and investigate their cosmological implications, paying particular attention in the interplay between these two constituents in different cosmological periods. Specifically, we consider a well-studied running vacuum model inspired by renormalization group, and a recently proposed general parameterization for the bulk viscosity $\xi$. By employing dynamical system analysis, we explore the physical aspects of the new phase space that emerges from the combined models and derive stability conditions that ensure complete cosmological dynamics. We identify four distinct classes of models and find that the critical points of the phase space are non-trivially renewed compared to the single scenarios. We then proceed, in a joint and complementary way to the dynamical system analysis, with a detailed numerical exploration to quantify the impact of both the running parameter and the bulk viscosity coefficient on the cosmological evolution. Thus, for some values of the model parameters, numerical solutions show qualitative differences from the $\Lambda$CDM model, which is phenomenologically appealing in light of cosmological observations.

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N. Cruz, G. Gomez, E. Gonzalez, et. al.
Wed, 26 Apr 23
42/62

Comments: 26 pages and 13 figures

New exact solutions in multi-scalar field cosmology [CL]

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http://arxiv.org/abs/2304.12360


We use the method of the superpotential to derive exact solutions describing inflationary cosmologies in multi-field models. An example that describes a solution that interpolates between two de Sitter universes is described in detail.

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J. Russo
Wed, 26 Apr 23
43/62

Comments: 16 pages, 4 figures

Inflationary E-models revisited [CEA]

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http://arxiv.org/abs/2304.12558


The E-type $\alpha$-attractor models of single-field inflation were generalized further in order to accommodate production of primordial black holes (PBH) via adding a near-inflection point to the inflaton scalar potential at smaller scales, in good agreement with measurements of the cosmic microwave background (CMB) radiation. A minimal number of new parameters was used but their fine-tuning was maximized in order to increase possible masses of PBH formed during an ultra-slow-roll phase leading to a large enhancement of the power spectrum of scalar (curvature) perturbations by 6 or 7 orders of magnitude against the power spectrum of perturbations observed in CMB. It was found that extreme fine-tuning of the parameters in our models can lead to a formation of the Earth-size PBH with the masses of approximately $10^{27}$ g, still in agreement with CMB observations. Quantum corrections are known to lead to the perturbative upper bound on the amplitude of large scalar perturbations responsible for PBH production. The quantum (one-loop) corrections in our models were found to be suppressed by one order of magnitude for PBH with the masses of approximately $10^{19}$ g, which may form the whole dark matter in the Universe.

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D. Frolovsky and S. Ketov
Wed, 26 Apr 23
50/62

Comments: 12 pages, 7 figures, LaTeX

Adiabatic and isocurvature perturbations in extended theories with non–minimally coupled fields [CL]

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http://arxiv.org/abs/2304.12364


The scalar field sector in low–energy effective field theories motivated by string theory often contains several scalar fields, some of which possess non–standard kinetic terms. In this paper, we study theories with two scalar fields, in which one of the fields has a non–canonical kinetic term. The kinetic coupling is allowed to depend on both fields, going beyond the work in the literature, which usually considers the case of the coupling to depend on the other field only. Our aim is to study adiabatic and isocurvature perturbations in these extended theories. Our results show that the evolution equation for the curvature perturbation does not change when allowing the coupling to depend on both fields, while the effective mass of the entropy perturbation changes. We find expressions for the spectral index and its running at horizon crossing and at the end of inflation. We apply the formalism and study three phenomenological models, with different kinetic couplings.

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M. Angelis and C. Bruck
Wed, 26 Apr 23
58/62

Comments: 17 pages, 3 figures

Initial conditions problem in cosmological inflation revisited [CL]

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http://arxiv.org/abs/2304.12150


We present first results from a novel numerical relativity code based on a tetrad formulation of the Einstein-scalar field equations combined with recently introduced gauge/frame invariant diagnostics indicating that inflation does not solve the homogeneity and isotropy problem beginning from generic initial conditions following a big bang.

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D. Garfinkle, A. Ijjas and P. Steinhardt
Wed, 26 Apr 23
62/62

Comments: 10 pages, 4 figures

Fifteen years of millimeter accuracy lunar laser ranging with APOLLO: data reduction and calibration [IMA]

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http://arxiv.org/abs/2304.11174


The Apache Point Lunar Laser-ranging Operation (APOLLO) has been collecting lunar range measurements for 15 years at millimeter accuracy. The median nightly range uncertainty since 2006 is 1.7 mm. A recently added Absolute Calibration System (ACS), providing an independent assessment of APOLLO system accuracy and the capability to correct lunar range data, revealed a 0.4% systematic error in the calibration of one piece of hardware that has been present for the entire history of APOLLO. Application of ACS-based timing corrections suggests systematic errors are reduced to < 1 mm, such that overall data accuracy and precision are both 1 mm. This paper describes the processing of APOLLO/ACS data that converts photon-by-photon range measurements into the aggregated normal points that are used for physics analyses. Additionally we present methodologies to estimate timing corrections for range data lacking contemporaneous ACS photons, including range data collected prior to installation of the ACS. We also provide access to the full 15-year archive of APOLLO normal points (2006-04-06 to 2020-12-27).

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N. Colmenares, J. Battat, D. Gonzales, et. al.
Tue, 25 Apr 23
23/72

Comments: 23 pages, 9 figures

Gravitational-Wave Phasing of Compact Binary Systems to the Fourth-and-a-Half post-Newtonian Order [CL]

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http://arxiv.org/abs/2304.11185


The inspiral phase of gravitational waves emitted by spinless compact binary systems is derived through the fourth-and-a-half post-Newtonian (4.5PN) order beyond quadrupole radiation, and the leading amplitude mode ($\ell$, m) = (2, 2) is obtained at 4PN order. We also provide the radiated flux, as well as the phase in the stationary phase approximation. Rough numerical estimates for the contribution of each PN order are provided for typical systems observed by current and future gravitational wave detectors.

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L. Blanchet, G. Faye, Q. Henry, et. al.
Tue, 25 Apr 23
47/72

Comments: 9 pages, 1 table

The $π$-axion and $π$-axiverse of dark QCD [CL]

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http://arxiv.org/abs/2304.11176


Axions and axion-like particles (ALPs) are a prominent dark matter candidate, drawing motivation in part from the axiverse of string theory. Axion-like particles can also arise as composite degrees of freedom of a dark sector, for example, as dark pions in dark Quantum Chromo-Dynamics. In a dark Standard Model (SM) wherein all 6 quark flavors are light while the photon is massive, one finds a rich low-energy spectrum of stable and ultralight particles, in the form of neutral and charged dark scalars, and complex neutral scalars analogous to the SM kaon, with mass splittings determined by the mass and charge of the dark quarks. The model finds a natural portal to the visible sector via kinetic coupling of the dark and visible photons, and consequent millicharges for dark matter. The dark matter can be a mixture of all these ultralight bosonic degrees of freedom, and exhibit both parity-even and parity-odd interactions, making the theory testable at a wide variety of experiments. In context of dark QCD with $N_f$ flavors of light quarks, this scenario predicts $N_f^2-1$ ultralight axion-like particles — effectively an axiverse from dark QCD. This ‘$\pi$-axiverse’ is consistent with but makes no recourse to string theory, and is complementary to the conventional string theory axiverse.

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S. Alexander, H. Gilmer, T. Manton, et. al.
Tue, 25 Apr 23
56/72

Comments: N/A

General-Relativistic Hydrodynamics Simulation of a Neutron Star – Sub-Solar-Mass Black Hole Merger [CL]

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http://arxiv.org/abs/2304.11642


Over the last few years, there has been an increasing interest in sub-solar mass black holes due to their potential to provide valuable information about cosmology or the black hole population. Motivated by this, we study observable phenomena connected to the merger of a sub-solar mass black hole with a neutron star. For this purpose, we perform new numerical-relativity simulations of a binary system composed of a black hole with mass $0.5M_\odot$ and a neutron star with mass $1.4 M_\odot$. We investigate the merger dynamics of this exotic system and provide information about the connected gravitational-wave and kilonova signals. Our study indicates that current gravitational-waveform models are unable to adequately describe such systems and that phenomenological relations connecting the binary parameters with the ejecta and remnant properties are not applicable to our system. Furthermore, we find a dependence of the kilonova signal on the azimuthal viewing angle due to the asymmetric mass ejection. This first-of-its-kind simulation opens the door for the study of sub-solar mass black hole – neutron star mergers and could serve as a testing ground for future model development.

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I. Markin, A. Neuweiler, A. Abac, et. al.
Tue, 25 Apr 23
67/72

Comments: 16 pages, 14 figures, to be submitted to PRD, comments welcome

Stochastic constant-roll inflation and primordial black holes [CEA]

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http://arxiv.org/abs/2304.10903


Stochastic inflation resolves primordial perturbations non-linearly, probing their probability distribution deep into its non-Gaussian tail. The strongest perturbations collapse into primordial black holes. In typical black-hole-producing single-field inflation, the strongest stochastic kicks occur during a period of constant roll. In this paper, I solve the stochastic constant-roll system, drawing the stochastic kicks from a numerically computed power spectrum, beyond the usual de Sitter approximation. The perturbation probability distribution is an analytical function of the integrated power spectrum $\sigma_k^2$ and the second slow-roll parameter $\epsilon_2$. With a large $\epsilon_2$, stochastic effects can reduce the height of the curvature power spectrum required to form asteroid mass black holes from $10^{-2}$ to $10^{-3}$. I compare these results to studies with the non-stochastic $\Delta N$ formalism.

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E. Tomberg
Mon, 24 Apr 23
7/41

Comments: 10 pages, 3 figures, 1 table

Synchronizing the Consistency Relation [CEA]

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http://arxiv.org/abs/2304.10559


We study the $N$-point function of the density contrast to quadratic order in the squeezed limit during the matter-dominated (MD) and radiation-dominated (RD) eras in synchronous gauge. Since synchronous gauge follows the free-fall frame of observers, the equivalence principle dictates that in the gradient approximation for the long-wavelength mode there is only a single, manifestly time-independent consistency relation for the $N$-point function. This simple form is dictated by the initial mapping between synchronous and local coordinates, unlike Newtonian gauge and its correspondingly separate dilation and Newtonian consistency relations. Dynamical effects only appear at quadratic order in the squeezed limit and are again characterized by a change in the local background, also known as the separate universe approach. We show that for the 3-point function the compatibility between these squeezed-limit relations and second-order perturbation theory requires both the initial and dynamical contributions to match, as they do in single-field inflation. This clarifies the role of evolution or late-time projection effects in establishing the consistency relation for observable bispectra, which is especially important for radiation acoustic oscillations and for establishing consistency below the matter-radiation equality scale in the MD era. Defining an appropriate angle and time average of these oscillations is also important for making separate universe predictions of spatially varying local observables during the RD era, which can be useful for a wider range of cosmological predictions beyond $N$-point functions.

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K. Inomata, H. Lee and W. Hu
Mon, 24 Apr 23
15/41

Comments: 65 pages, 1 figure

Running vacuum in the Universe: phenomenological status in light of the latest observations, and its impact on the $σ_8$ and $H_0$ tensions [CEA]

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http://arxiv.org/abs/2304.11157


A substantial body of phenomenological and theoretical work over the last few years strengthens the possibility that the vacuum energy density (VED) of the universe is dynamical, and in particular that it adopts the running vacuum model' (RVM) form, in which the VED evolves mildly as $\delta \rho_{\rm vac}(H)\sim \nu_{\rm eff} m_{\rm Pl}^2{\cal O}\left(H^2\right)$, where $H$ is the Hubble rate and $\nu_{\rm eff}$ is a (small) free parameter. This dynamical scenario is grounded on recent studies of quantum field theory (QFT) in curved spacetime and also on string theory. It turns out that what we call thecosmological constant’, $\Lambda$, is no longer a rigid parameter but the nearly sustained value of $8\pi G(H)\rho_{\rm vac}(H)$ around (any) given epoch $H(t)$, where $G(H)$ is the gravitational coupling, which can also be very mildly running (logarithmically). Of particular interest is the possibility suggested in past works that such a running may help to cure the cosmological tensions afflicting the $\Lambda$CDM. In the current study, we reanalyze it in full and we find it becomes further buttressed. Using the modern cosmological data, namely a compilation of the latest $SNIa+BAO+$H(z)$+LSS+CMB$ observations, we probe to which extent the RVM provides a quality fit better than the concordance $\Lambda$CDM model, paying particular emphasis on its impact on the $\sigma_8$ and $H_0$ tensions. We utilize the Einstein-Boltzmann system solver $CLASS$ and the Monte Carlo sampler $MontePython$ for the statistical analysis, as well as the statistical $DIC$ criterion to compare the running vacuum against the rigid vacuum ($\nu_{\rm eff} = 0$). We show that with a tiny amount of vacuum dynamics ($|\nu_{\rm eff}|\ll 1$) the global fit can improve significantly with respect to the $\Lambda$CDM and the mentioned tensions may subside to inconspicuous levels.

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J. Peracaula, A. Gomez-Valent, J. Perez, et. al.
Mon, 24 Apr 23
20/41

Comments: LaTeX, 44 pages, 11 Tables and 4 Figures

High-Frequency Gravitational Wave Detection via Optical Frequency Modulation [CL]

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http://arxiv.org/abs/2304.10579


High-frequency gravitational waves can be detected by observing the frequency modulation they impart on photons. We discuss fundamental limitations to this method related to the fact that it is impossible to construct a perfectly rigid detector. We then propose several novel methods to search for O(MHz-GHz) gravitational waves based on the frequency modulation induced in the spectrum of an intense laser beam, by applying optical frequency demodulation techniques, or by using optical atomic clock technology. We find promising sensitivities across a broad frequency range.

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T. Bringmann, V. Domcke, E. Fuchs, et. al.
Mon, 24 Apr 23
21/41

Comments: 11 pages, 3 figures

Gravitationally modulated quantum correlations: Discriminating classical and quantum models of ultra-compact objects with Bell nonlocality [CL]

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http://arxiv.org/abs/2304.10868


We investigate the relation between quantum nonlocality and gravity at the astrophysical scale, both in the classical and quantum regimes. Considering particle pairs orbiting in the strong gravitational field of ultra-compact objects, we find that the violation of Bell inequality acquires an angular modulation factor that strongly depends on the nature of the gravitational source. We show how such gravitationally-induced modulation of quantum nonlocality readily discriminates between black holes (both classical and inclusive of quantum corrections) and string fuzzballs, i.e., the true quantum description of ultra-compact objects according to string theory. These findings promote Bell nonlocality as a potentially key tool in comparing different models of classical and quantum gravity and putting them to the test.

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L. Petruzziello and F. Illuminati
Mon, 24 Apr 23
27/41

Comments: 12 pages, 4 figures

Disformal symmetry in the Universe: mimetic gravity and beyond [CL]

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http://arxiv.org/abs/2304.11035


Symmetries play an important role in fundamental physics. In gravity and field theories, particular attention has been paid to Weyl (or conformal) symmetry. However, once the theory contains a scalar field, conformal transformations of the metric can be considered a subclass of a more general type of transformation, so-called disformal transformation. Here, we investigate the implications of pure disformal symmetry in the Universe. We derive the form of general disformal invariant tensors from which we build the most general disformal invariant action. We argue that, in cosmology, disformal symmetry amounts to require that the lapse function is fully replaced by a (time-like) scalar field at the level of the action. We then show that disformal symmetry is in general an exactly equivalent formulation of general mimetic gravity. Lastly, we go beyond mimetic gravity and find that a particular class of invariance leads to seemingly Ostrogradski-like (with higher derivatives) Lagrangians, which are nevertheless absent of Ostrogradski ghosts in a cosmological background, despite having an additional degree of freedom. We also propose an application of our formalism to find new invertible disformal transformations, where the coefficient involves higher derivatives and curvature, further expanding the theory space of scalar-tensor theories.

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G. Domènech and A. Ganz
Mon, 24 Apr 23
33/41

Comments: 21 pages

Slow Contraction and the Weyl Curvature Hypothesis [CL]

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http://arxiv.org/abs/2304.10030


Using the power of numerical relativity, we show that, beginning from generic initial conditions that are far from flat, homogeneous and isotropic and have a large Weyl curvature, a period of slow contraction rapidly drives spacetime towards vanishingly small Weyl curvature as the total energy density grows, thus providing a dynamical mechanism that satisfies the Weyl Curvature Hypothesis. We also demonstrate a tight correlation between the Weyl Curvature Hypothesis and ultralocal behavior for canonical scalar fields with a sufficiently steep negative potential energy density.

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A. Ijjas
Mon, 24 Apr 23
34/41

Comments: 5 pages, 5 figures

Fifteen years of millimeter accuracy lunar laser ranging with APOLLO: dataset characterization [IMA]

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http://arxiv.org/abs/2304.11128


We present data from the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) covering the 15-year span from April 2006 through the end of 2020. APOLLO measures the earth-moon separation by recording the round-trip travel time of photons from the Apache Point Observatory to five retro-reflector arrays on the moon. The APOLLO data set, combined with the 50-year archive of measurements from other lunar laser ranging (LLR) stations, can be used to probe fundamental physics such as gravity and Lorentz symmetry, as well as properties of the moon itself. We show that range measurements performed by APOLLO since 2006 have a median nightly accuracy of 1.7 mm, which is significantly better than other LLR stations.

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J. Battat, E. Adelberger, N. Colmenares, et. al.
Mon, 24 Apr 23
38/41

Comments: 16 pages, 9 figures

GSpyNetTree: A signal-vs-glitch classifier for gravitational-wave event candidates [CL]

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http://arxiv.org/abs/2304.09977


Despite achieving sensitivities capable of detecting the extremely small amplitude of gravitational waves (GWs), LIGO and Virgo detector data contain frequent bursts of non-Gaussian transient noise, commonly known as ‘glitches’. Glitches come in various time-frequency morphologies, and they are particularly challenging when they mimic the form of real GWs. Given the higher expected event rate in the next observing run (O4), LIGO-Virgo GW event candidate validation will require increased levels of automation. Gravity Spy, a machine learning tool that successfully classified common types of LIGO and Virgo glitches in previous observing runs, has the potential to be restructured as a signal-vs-glitch classifier to accurately distinguish between glitches and GW signals. A signal-vs-glitch classifier used for automation must be robust and compatible with a broad array of background noise, new sources of glitches, and the likely occurrence of overlapping glitches and GWs. We present GSpyNetTree, the Gravity Spy Convolutional Neural Network Decision Tree: a multi-CNN classifier using CNNs in a decision tree sorted via total GW candidate mass tested under these realistic O4-era scenarios.

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S. Alvarez-Lopez, A. Liyanage, J. Ding, et. al.
Fri, 21 Apr 23
23/60

Comments: 19 pages, 12 figures, submitted to Classical and Quantum Gravity

Measuring the Hubble Constant Using Strongly Lensed Gravitational Wave Signals [CEA]

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http://arxiv.org/abs/2304.10435


The measurement of the Hubble constant $H_0$ plays an important role in the study of cosmology. In this letter, we propose a new method to constrain the Hubble constant using the strongly lensed gravitational wave (GW) signals. By reparameterizing the waveform, we find that the lensed waveform is sensitive to the $H_0$. Assuming the scenario that no electromagnetic counterpart of the GW source can be identified, our method can still give meaningful constraints on the $H_0$ with the information of the lens redshift. We then apply Fisher information matrix and Markov Chain Monte Carlo to evaluate the potential of this method. For the space-based GW detector, TianQin, the $H_0$ can be constrained within a relative error of $\sim$ 0.3-2\%, using a single strongly lensed GW event. Precision varies according to different levels of electromagnetic information.

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S. Huang, Y. Hu, X. Chen, et. al.
Fri, 21 Apr 23
29/60

Comments: 7 pages, 4 figures

Black holes in classical general relativity and beyond [CL]

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http://arxiv.org/abs/2304.09984


The Kerr-Newman metric is the unique vacuum solution of the General Relativistic field equations, in which any singularities or spacetime pathologies are hidden behind horizons. They are believed to describe the spacetimes of massive astrophysical objects with no surfaces, which we call black holes. This spacetime, which is defined entirely by the mass, spin, and charge of the black hole, gives rise to a variety of phenomena in the motion of particles and photons outside the horizons that have no Newtonian counterparts. Moreover, the Kerr-Newman spacetime remains remarkably resilient to many attempts in modifying the underlying theory of gravity. The monitoring of stellar orbits around supermassive black holes, the detection of gravitational waves from the coalescence of stellar-mass black holes, and the observation of black-hole shadows in images with horizon-scale resolution, all of which have become possible during the last decade, are offering valuable tools in testing quantitatively the predictions of this remarkable solution to Einstein’s equations.

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D. Psaltis
Fri, 21 Apr 23
35/60

Comments: This chapter is the pre-print of the version currently in production. Please cite this chapter as the following: D. Psaltis. “Black holes in classical general relativity and beyond” in The Encyclopedia of Cosmology (Set 2): Black Holes, edited by Z. Haiman (World Scientific, New Jersey, 2023)

Localization of binary neutron star mergers with a single Cosmic Explorer [HEAP]

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http://arxiv.org/abs/2304.09889


Next-generation ground-based gravitational-wave detectors, such as Cosmic Explorer (CE), are expected to be sensitive to gravitational-wave signals with frequencies as low as 5 Hz, allowing signals to spend a significant amount of time in the detector frequency band. As a result, the effects caused by the rotation of the Earth become increasingly important for such signals. Additionally, the length of the arms of these detectors can be comparable to the wavelength of detectable gravitational waves, which introduces frequency-dependent effects that are not significant in current-generation detectors. These effects are expected to improve the ability to localize compact binary coalescences in the sky even when using only one detector. This study aims to understand how much these effects can help in localization. We present the first comprehensive Bayesian parameter estimation framework that accounts for all these effects using \textsc{Bilby}, a commonly used Bayesian parameter estimation tool. We focus on sky localization constraints for binary neutron star events with an optimal signal-to-noise ratio of 1000 with one detector at the projected CE sensitivity. We find that these effects help localize sources using one detector with sky areas as low as 10 square degrees. Moreover, we explore and discuss how ignoring these effects in the parameter estimation can lead to biases in the inference.

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P. Baral, S. Morisaki, I. Hernandez, et. al.
Fri, 21 Apr 23
41/60

Comments: N/A

The Challenge of Eccentricity when Observing Stellar-mass Binary Black Holes with Space-Based Gravitational Wave Detectors [HEAP]

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http://arxiv.org/abs/2304.10340


Eccentricity is a smoking gun for the formation channel of stellar-mass binary black holes (sBBHs). Space-based gravitational wave observatories can determine binary eccentricity to $e_0\gtrsim\mathcal{O}(10^{-4}) $, but the detection of these systems can be very challenging. A targeted search of archival data triggered by ground-based detectors shrinks the search range thus making the task tractable. Previous studies ignored the effect of eccentricity. For the first time, we constructed a template bank for space-borne gravitational wave detectors that includes the impact of eccentricity. We find that even for a mild upper limit of $0.1$, the inclusion of eccentricity can still boost the template bank size by five orders of magnitudes. Our work marked a solid step towards the detection of a realistic sBBH, and it demonstrated that with the appropriate extension, the template bank method can still identify the early inspiral of sBBHs.

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H. Wang, I. Harry, A. Nitz, et. al.
Fri, 21 Apr 23
44/60

Comments: 7 pages, 3 figures, comments welcome

Testing the first law of black hole mechanics with gravitational waves [CL]

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http://arxiv.org/abs/2304.10117


GW191219_163120 is a gravitational wave signal that is believed to have originated from a neutron star-black hole (NSBH) coalescence with an extreme mass ratio. In this work, we use data of GW191219_163120 from LIGO and Virgo to test the first law of black hole mechanics by considering the neutron star as a perturbation to the black hole before the merger, and the remnant black hole as a stationary black hole after the merger. Our results demonstrate consistency with the first law of black hole mechanics, with an error level of about 6\% at 68\% credibility and 10\% at 95\% credibility. We also find that the higher the mass ratio of the gravitational wave source, the more consistent our results are with the first law of black hole mechanics. Overall, our study sheds light on the nature of NSBH coalescences and their implications for black hole mechanics.

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C. Wang and F. Shu
Fri, 21 Apr 23
55/60

Comments: 5 pages, 4 figures, 2 tables

Comment on "Observational Evidence for Cosmological Coupling of Black Holes and its Implications for an Astrophysical Source of Dark Energy" [CL]

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http://arxiv.org/abs/2304.09817


It was recently claimed that black holes can explain the accelerated expansion of the universe. Here we point out that this claim is based on a confusion about the principle of least action, undermining the link between black holes and dark energy.

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T. Mistele
Thu, 20 Apr 23
12/57

Comments: 5 pages

Neutron Stars on Modified Teleparallel Gravity [CL]

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http://arxiv.org/abs/2301.06432


We investigate compact objects in modified teleparallel gravity with realistic equations of state. We propose a modification on Teleparallel Equivalent of General Relativity, then an appropriate tetrad is applied on the field equations. A specific set of relations showing a equivalency between our gravitational model and the New General Relativity is found. The conservation equation implies that our Tolman-Oppenheimer-Volkoff equations are presented with an effective pressure and energy density, where a free parameter \b{eta}3 is used to construct them. Numerical analysis using realistic equations of state is made, the behavior of mass, radius and the relation mass-radius as functions of \b{eta}3 is also investigated.

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S. Vilhena, S. Duarte, M. Dutra, et. al.
Thu, 20 Apr 23
17/57

Comments: 8 pages, 5 figures

The spin and mass ratio affects the gravitational waveforms of binary black hole mergers with a total system mass of 12-130 $\rm{M}_\odot$ [HEAP]

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http://arxiv.org/abs/2304.09396


Analyzing the observations obtained by the LIGO and the Virgo Collaborations, a new era has begun in binary black hole (BBH) merger processes and black hole physics studies. The fact that very massive stars that will become black holes at the end of their evolution are in binary or multiple states adds particular importance to BBH studies. In this study, using the SEOBNRv4$_opt$ gravitational waveform model developed for compact binary systems, many ($\sim 10^6$) models were produced under different initial conditions, and the pre- and post-merge parameters were compared. In the models, it is assumed that the initial total mass (M${\rm{tot}}$) of the binary systems varies between 12-130 $\rm{M}\odot$ with step interval 1$\rm{M}\odot$, the mass ratios ($q = \rm{m}{1i}/\rm{m}{2i}$) vary between 1 and 2 with step interval 0.004, and the initial spin ($\abs{\rchi{1i}} = \abs{\rchi_{2i}}$) value varies between $-0.83$ and $+0.83$ with step interval 0.017. Final spin ($\rchi_{f}$), fractional mass loss (M${FL}$), and the maximum gravitational wave amplitude (h${\rm{max}}$) obtained during the merger were compared with appropriate tables and figures obtained from the results of the relativistic numeric model obtained according to the initial parameters. Our results show that M${\rm{FL}}$ in generated BBH coalescences varied about 2.7 to 9.2\%, and $\rchi{\rm{f}}$ between 0.29 and 0.91. In most of the BBHs we have modeled, we found that M${\rm{FL}}$ varies inversely with $q$. However, it has been found that M${\rm{FL}}$ values are not always inversely varied to the $q$ parameter in systems of opposite initial spin, where the large mass black hole component is positively oriented. Accordingly, it is understood that the values of M$_{\rm{FL}}$ decrease to a certain point of $q$ and then increase according to the increasing direction of $q$.

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&. Özbakır and K. Yakut
Thu, 20 Apr 23
23/57

Comments: 29 pages, 5 figure, 5 tables, submitted for publication

Clockwork Cosmology [CL]

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http://arxiv.org/abs/2304.09205


The higher order generalisation of the clockwork mechanism to gravitational interactions provides a means to generate an exponentially suppressed coupling to matter from a fundamental theory of multiple interacting gravitons, without introducing large hierarchies in the underlying potential and without the need for a dilaton, suggesting a possible application to the hierarchy problem. We work in the framework of ghost free multi-gravity with “nearest-neighbour” interactions, and present a formalism by which one is able to construct potentials such that the theory will always exhibit this clockwork effect. We also consider cosmological solutions to the general theory, where all metrics are of FRW form, with site-dependent scale factors/lapses. We demonstrate the existence of multiple deSitter vacua where all metrics share the same Hubble parameter, and we solve the modified Einstein equations numerically for an example clockwork model constructed using our formalism, finding that the evolution of the metric that matter couples to is essentially equivalent to that of general relativity at the modified Planck scale. It is important to stress that while we focus on the application to clockwork theories, our work is entirely general and facilitates finding cosmological solutions to any ghost free multi-gravity theory with “nearest-neighbour” interactions. Moreover, we clarify previous work on the continuum limit of the theory, which is generically a scalar-tensor braneworld, using the Randall-Sundrum model as a special case and showing how the discrete-clockwork cosmological results map to the continuum results in the appropriate limit.

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K. Wood, P. Saffin and A. Avgoustidis
Thu, 20 Apr 23
27/57

Comments: 48 pages, 4 figures

On the energy flow of $λ$ in Hořava-Lifshitz cosmology [CEA]

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http://arxiv.org/abs/2304.09766


Ho\v{r}ava-Lifshitz gravity has been proposed as a ghost-free quantum gravity model candidate with an anisotropic UV-scaling between space and time. We present here a cosmological background analysis of two different formulations of the theory, with particular focus on the running of the parameter $\lambda$. Using a large dataset consisting of Cosmic Microwave Background data from {\it Planck}, Pantheon+ supernovae catalogue, SH0ES Cepheid variable stars, Baryon acoustic oscillations (BAO), Cosmic Chronometers, and gamma-ray bursts (GRB), we arrive at new bounds on the cosmological parameters, in particular $\lambda$, which describes deviation from classical general relativity. For the detailed balance scenario we arrive at the bound $\lambda=1.02726\pm0.00012$, and for beyond detailed balance the limit reads $\lambda=0.9949^{+0.0045}_{-0.0046}$. We also study the influence of different data sets and priors, and we find that removing low-redshift data generally moves $\lambda$ closer towards UV values, whilst simultaneously widening the error bars. In the detailed balance scenario, this effect is more noticeable, and $\lambda$ takes on values that are significantly below unity, which corresponds to the infrared limit of the theory.

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E. Czuchry and N. Nilsson
Thu, 20 Apr 23
30/57

Comments: 16 pages, 2 tables, 1 figure

Confronting strange stars with compact-star observations and new physics [HEAP]

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http://arxiv.org/abs/2304.09614


Strange stars ought to exist in the universe according to the strange quark matter hypothesis, which states that matter made of roughly equal numbers of up, down, and strange quarks could be the true ground state of baryonic matter rather than ordinary atomic nuclei. Theoretical models of strange quark matter, such as the standard MIT bag model, the density-dependent quark mass model, or the quasi-particle model, however, appear to be unable to reproduce some of the properties (masses, radii and tidal deformabilities) of recently observed compact stars. This is different if alternative gravity theory (e.g., non-Newtonian gravity) or dark matter (e.g., mirror dark matter) are considered, which resolve these issues. The possible existence of strange stars could thus provide a clue to new physics, as discussed in this review.

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S. Yang, C. Pi, X. Zheng, et. al.
Thu, 20 Apr 23
38/57

Comments: 26 pages, 11 figures. Review paper accepted for publication in Universe

Dark matter effects in modified teleparallel gravity [CL]

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http://arxiv.org/abs/2304.07364


This work investigates dark matter (DM) effects in compact objects in modified teleparallel gravity (MTG) in which a modification of Teleparallel Equivalent to General Relativity is used. We applied a tetrad to the modified field equations where a set of relations is found. The conservation equation allows us to rewrite our Tolman-Oppenheimer-Volkoff equations with an effective gravitational coupling constant. As input to these new equations, we use a relativistic mean-field (RMF) model with dark matter content included, obtained from a Lagrangian density with both, hadronic and dark particle degrees of freedom, as well as the Higgs boson, used as a mediator in both sectors of the theory. Through numerical calculations, we analyze the mass-radius diagrams obtained from different parametrizations of the RMF-DM model, generated by assuming different values of the dark particle Fermi momentum and running the free parameter coming from the MTG. Our results show that it is possible for the system simultaneously support more DM content, and be compatible with recent astrophysical data provided by LIGO and Virgo Collaboration, as well as by NASA’s Neutron star Interior Composition Explorer (NICER).

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S. Vilhena, M. Dutra, O. Lourenço, et. al.
Thu, 20 Apr 23
44/57

Comments: 8 pages, 2 figures

BCS in the Sky: Signatures of Inflationary Fermion Condensation [CL]

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http://arxiv.org/abs/2304.09428


We consider a Bardeen-Cooper-Schrieffer (BCS)-like model in the inflationary background. We show that with an axial chemical potential, the attractive quartic fermion self-interaction can lead to a BCS-like condensation. In the de Sitter (dS) limit of inflation, we perform the first computation of the non-perturbative effective potential that includes the full spacetime curvature effects in the presence of the chemical potential. The corresponding BCS phase transition is always first-order, when the varying Hubble is interpreted as an effective Gibbons-Hawking temperature of dS spacetime. In the condensate phase, the theory can be understood from UV and IR sides as fermionic and bosonic, respectively. This leads to distinctive signatures in the primordial non-Gaussianity of curvature perturbations. Namely, the oscillatory cosmological collider signal is smoothly turned off at a finite momentum ratio, since different momentum ratios effectively probe different energy scales. In addition, such BCS phase transitions can also source stochastic gravitational waves, feasible for future experiments.

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X. Tong, Y. Wang, C. Zhang, et. al.
Thu, 20 Apr 23
48/57

Comments: 30 pages, 8 figures

A Sun-like star orbiting a boson star [SSA]

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http://arxiv.org/abs/2304.09140


The high-precision astrometric mission GAIA recently reported the remarkable discovery of a Sun-like star closely orbiting a dark object, with a semi-major axis and period of $1.4\, \rm{AU}$ and $187.8$ days respectively. While the plausible expectation for the central dark object is a black hole, the evolutionary mechanism leading to the formation of such a two-body system is highly challenging. Here, we challenge the scenario of a central black hole and show that the observed orbital dynamics can be explained under fairly general assumptions if the central dark object is a stable clump of bosonic particles of spin-0, or spin-1, known as a boson star. We further explain how future astrometric measurements of similar systems will provide an exciting opportunity to probe the fundamental nature of compact objects and test compact alternatives to black holes.

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A. Pombo and I. Saltas
Wed, 19 Apr 23
8/58

Comments: 11 pages, 4 figures. Comments are very welcome

Gauge/frame invariant variables for the numerical relativity study of cosmological spacetimes [CL]

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http://arxiv.org/abs/2304.07616


To numerically evolve the full Einstein equations (or modifications thereof), simulations of cosmological spacetimes must rely on a particular formulation of the field equations combined with a specific gauge/frame choice. Yet truly physical results cannot depend on the given formulation or gauge/frame choice. In this paper, we present a resolution of the gauge problem and, as an example, numerically implement it to evaluate our previous work on contracting spacetimes.

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A. Ijjas
Wed, 19 Apr 23
14/58

Comments: 22 pages, 8 figures

Effective description of generalized disformal theories [CL]

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http://arxiv.org/abs/2304.08624


Generalized disformal transformations enable us to construct the generalized disformal Horndeski theories, which form the most general class of ghost-free scalar-tensor theories to this date. We extend the effective field theory (EFT) of cosmological perturbations to incorporate these generalized disformal Horndeski theories. The main difference from the conventional EFT is that our extended EFT involves operators with higher spatial derivatives of the lapse function. Our EFT also accommodates the generalized disformal transformation of U-DHOST theories.

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K. Takahashi, M. Minamitsuji and H. Motohashi
Wed, 19 Apr 23
26/58

Comments: 14 pages

Tests of modified gravitational wave propagations with gravitational waves [CL]

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http://arxiv.org/abs/2304.09025


Any violation of the fundamental principles of general relativity (GR), including the violations of the equivalence principle and parity/Lorentz symmetries, could induce possible derivations in the gravitational wave (GW) propagations so they can be tested/constrained directly by the GW data. In this letter, we present a universal parametrization for characterizing possible derivations from GW propagations in GR. This parametrization provides a general framework for exploring possible modified GW propagations arising from a large number of modified theories of gravity. With this parameterization, we construct the modified GW waveforms generated by the coalescence of compact binaries with the effects of the gravitational parity/Lorentz violations, then analyze the open data of compact binary merging events detected by LIGO/Virgo/KAGRA collaboration. We do not find any signatures of gravitational parity/Lorentz violations, thereby allowing us to place several of the most stringent constraints on parity/Lorentz violations in gravity and a first constraint on the Lorentz-violating damping effect in GW. This also represents the most comprehensive tests on the modified GW propagations.

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T. Zhu, W. Zhao, J. Yan, et. al.
Wed, 19 Apr 23
36/58

Comments: 6 pages, 3 tables, and 1 figure

A Dark Matter Probe in Accreting Pulsar-Black Hole Binaries [HEAP]

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http://arxiv.org/abs/2304.08824


The accretion of dark matter (DM) into astrophysical black holes slowly increases their mass. The rate of this mass accretion depends on the DM model and the model parameters. If this mass accretion effect can be measured accurately enough, it is possible to rule out some DM models, and, with the sufficient technology and the help of other DM constraints, possibly confirm one model. We propose a DM probe based on accreting pulsar-black hole binaries, which provide a high-precision measurement on binary orbital phase shifts induced by DM accretion into black holes, and can help rule out DM models and study the nature of DM.

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A. Akil and Q. Ding
Wed, 19 Apr 23
50/58

Comments: 11 pages, 4 figures

Anisotropic power-law inflation for a generalized model of two scalar and two vector fields [CL]

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http://arxiv.org/abs/2304.08874


Cosmological implication of a generalized model of two scalar and two vector fields, in which both scalar fields are non-minimally coupled to each vector field, is studied in this paper. In particular, we will seek an anisotropic power-law inflationary solution to this model. Furthermore, the stability of the obtained solution will be examined by using the dynamical system approach. As a result, we will show that this solution turns out to be stable and attractive during the inflationary phase as expected due to the existence of the unusual couplings between two scalar and two vector fields. Remarkably, we will point out that the existence of phantom field will lead to an instability of the corresponding anisotropic power-law inflation.

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T. Do and W. Kao
Wed, 19 Apr 23
51/58

Comments: 20 pages, 6 figures. Comments are welcome. arXiv admin note: text overlap with arXiv:2110.13516

Trajectories of astroparticles in pseudo-Finsler spacetime with the most general modified dispersion [CL]

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http://arxiv.org/abs/2304.08676


Finsler geometry is a natural and fundamental generalization of Riemann geometry, and is a tool to research Lorentz invariance violation. We find the connection between the most general modified dispersion relation and a pseudo-Finsler structure, and then we calculate the arrival time delay of astroparticles with different modified dispersion relations in the framework of Finsler geometry. The result suggests that the time delay is irrelevant with the exact form of the modified dispersion relation. If the modified term becomes 0 when $E=p$, there is no arrival time difference, otherwise the time delays only depend on the Lorentz violation scale and the order at which the Lorentz invariance breaks.

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J. Zhu and B. Ma
Wed, 19 Apr 23
53/58

Comments: 9 pages, no figure, version for journal publication

Supermassive primordial black holes: a view from clustering of quasars at $z \sim 6$ [CEA]

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http://arxiv.org/abs/2304.08153


We investigate a scenario where primordial black holes (PBHs) can be the progenitors of supermassive black holes (SMBHs) observed at $z\sim6$. To this end, we carried out clustering analysis using a sample of 81 quasars at $5.88 <z<6.49$, which is constructed in Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) project, and 11 quasars in the same redshift range selected from the literature. The resulting angular auto-correlation function (ACF) can be fitted to a power-law form of $\omega_\theta = 0.045^{+0.114}_{-0.106}~\theta^{-0.8}$ over a scale of $0.2!-!10$ degrees. We compare the ACF of the quasars to that predicted for the PBH model at $z\sim 6$ and found that such a scenario is excluded for a broad range of parameter space, from which we can conclude that a scenario with PBHs as SMBHs is not viable. We also discuss a model in which SMBHs at $z \sim 6$ originate from the direct collapse of PBH clumps and argue that the observed ACF excludes such a scenario in the context of our PBH model.

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T. Shinohara, W. He, Y. Matsuoka, et. al.
Tue, 18 Apr 23
1/80

Comments: 23 pages, 7 figures

Exploring the multi-band gravitational wave background with a semi-analytic galaxy formation model [CL]

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http://arxiv.org/abs/2304.08333


The compact binary systems, spanning from the stellar to supermassive black hole, encode a wealth of information concerning stellar evolution, galaxy formation and evolution, and cosmology. An enormous number of these systems, both resolved and unresolved, emit substantial gravitational waves during their final evolutionary stages, thereby creating a stochastic gravitational wave background (SGWB). We calculate the merger rates of stellar compact binaries and massive black hole binaries using a semi-analytic galaxy formation model — Galaxy Assembly with Binary Evolution (GABE) in a unified and self-consistent approach, followed by an estimation of the multi-band SGWB contributed by the binary systems. We find that the amplitudes of the principal peaks of the SGWB energy density are within one order of magnitude $\Omega_{GW} \sim 10^{-9}- 10^{-8}$. This SGWB can be easily detected by the Square Kilometre Array (SKA), as well as planned interferometric detectors, such as the Einstein Telescope (ET) and the Laser Interferometer Space Antenna (LISA). The energy density of this background varies as $\Omega_{GW} \propto f^{2/3}$ in the SKA band. The shape of the SGWB spectrum in the frequency range $\sim[10^{-4}$,$1]$Hz could allow the space-based detector LISA to distinguish the black hole seed models. The amplitude of the SGWB from merging stellar binary black holes (BBHs) at $\sim 100$ Hz is approximately 10 and 100 times greater than those from merging binary neutron stars (BNSs) and neutron-star-black-hole (NSBH) mergers, respectively.

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Z. Li, Z. Jiang, X. Fan, et. al.
Tue, 18 Apr 23
36/80

Comments: 9 pages, 4 figures

LISAmax: Improving the Gravitational-Wave Sensitivity by Two Orders of Magnitude [CL]

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http://arxiv.org/abs/2304.08287


Within its Voyage 2050 planning cycle, the European Space Agency (ESA) is considering long-term large class science mission themes. Gravitational-wave astronomy is among the topics under study. This paper presents “LISAmax”, a gravitational-wave interferometer concept consisting of three spacecraft located close to the Sun-Earth libration points L3, L4 and L5, forming a triangular constellation with an arm length of 259 million kilometers (to be compared to LISA’s 2.5 million kilometer arms). This is the largest triangular formation that can be reached from Earth without a major leap in mission complexity and cost. The sensitivity curve of such a detector is at least two orders of magnitude lower in amplitude than that of LISA. Depending on the choice of other instrument parameters, this makes the detector sensitive to gravitational waves in the micro-Hertz range and opens a new window for gravitational-wave astronomy, not covered by any other planned detector concept. We analyze in detail the constellation stability for a 10-year mission in the full numerical model and compute the orbit transfers using a European launcher and chemical propulsion. The payload design parameters are assessed, and the expected sensitivity curve is compared with a number of potential gravitational-wave sources. No show stoppers are identified at this point of the analysis.

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W. Martens, M. Khan and J. Bayle
Tue, 18 Apr 23
45/80

Comments: 18 pages, 11 figures