Tag Archives: General Relativity and Quantum Cosmology

Intelligent noise suppression for gravitational wave observational data [CL]

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http://arxiv.org/abs/2212.14283


With the advent of gravitational-wave astronomy and the discovery of more compact binary coalescences, data quality improvement techniques are desired to handle the complex and overwhelming noise in gravitational wave (GW) observational data. Though recent studies have shown promising results for data denoising, they are unable to precisely recover both the GW signal amplitude and phase. To address such an issue, we develop a deep neural network centered workflow, WaveFormer, for significant noise suppression and signal recovery on observational data from the Laser Interferometer Gravitational-Wave Observatory (LIGO). The WaveFormer has a science-driven architecture design with hierarchical feature extraction across a broad frequency spectrum. As a result, the overall noise and glitch are decreased by more than 1 order of magnitude and the signal recovery error is roughly 1% and 7% for the phase and amplitude, respectively. Moreover, we achieve state-of-the-art accuracy on reported binary black hole events of existing LIGO observing runs and substantial 1386 years inverse false alarm rate improvement on average. Our work highlights the potential of large neural networks for GW data quality improvement and can be extended to the data processing analyses of upcoming observing runs.

Read this paper on arXiv…

Z. Ren, H. Wang, Y. Zhou, et. al.
Mon, 2 Jan 23
41/44

Comments: N/A

The effective Equation of State in Palatini $f(R)$ cosmology [CL]

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http://arxiv.org/abs/2212.13825


We investigate how the cosmological Equation of State can be used for scrutinizing extended theories of gravity, in particular, the Palatini $f(R)$ gravity. Specifically, the approach consists, at first, in investigating the effective Equation of State produced by a given model. Then, the inverse problem can also be considered in view of determining which models are compatible with a given effective Equation of State. We consider and solve some cases and show that, for example, power-law models are (the only models) capable of transforming barotropic Equations of State into effective barotropic ones. Moreover, the form of Equation of State is preserved (only) for $f(R)=R$, as expected. In this perspective, modified Equations of State are a feature capable of distinguishing Extended Gravity with respect to General Relativity. We also investigate quadratic and non-homogeneous effective Equations of State showing, in particular, that they contain the Starobinsky model and other ones.

Read this paper on arXiv…

S. S.Camera, S. S.Capozziello, L. L.Fatibene, et. al.
Thu, 29 Dec 22
1/47

Comments: 19 pages

First statistical measurement of the Hubble constant using unlocalized fast radio bursts [CEA]

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http://arxiv.org/abs/2212.13433


Fast radio bursts (FRBs) can be used to measure the Hubble constant by employing the Macquart relation. However, at present, only a small number of FRB events are localized to their host galaxies with known redshifts. In this paper, we develop a Bayesian method to statistically measure the Hubble constant using unlocalized FRBs and galaxy catalog data, which makes it possible to constrain cosmological parameters by using a large number of FRB data without known redshift information. Using the six FRB events observed by ASKAP combined with the big bang nucleosynthesis result, we obtain $H_0=71.7^{+8.8}{-7.4}$ km s$^{-1}$ Mpc$^{-1}$ in the simulation-based case and $H_0=71.5^{+10.0}{-8.1}$ km s$^{-1}$ Mpc$^{-1}$ in the observation-based case ($68\%$ highest-density interval), assuming different host galaxy population parameters. We also estimate that in the next few years, using thousands of FRBs could achieve a $3\%$ precision on the random error of the Hubble constant.

Read this paper on arXiv…

Z. Zhao, J. Zhang, Y. Li, et. al.
Thu, 29 Dec 22
2/47

Comments: 9 pages, 3 figures

Imprint of galactic rotation curves and metric fluctuations on the recombination era anisotropy [CEA]

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http://arxiv.org/abs/2212.13942


In applications of the conformal gravity theory it has been shown that a scale of order 105 Mpc due to large scale inhomogeneities such as clusters of galaxies is imprinted on the rotation curves of galaxies. Here we show that this same scale is imprinted on recombination era anisotropies in the cosmic microwave background. We revisit an analysis due to Mannheim and Horne, to show that in the conformal gravity theory the length scale of metric signals that originate in the primordial nucleosynthesis era at $10^{9\circ}$K can fill out the entire recombination era sky. Similarly, the length scale of acoustic signals that originate at $10^{13\circ}$K can also fill out the entire recombination era sky. We show that the amplitudes of metric fluctuations that originate in the nucleosynthesis era can grow by a factor of $10^{12}$ at recombination, and by a factor of $10^{18}$ at the current time. In addition we find that without any period of exponential expansion a length scale as small as $10^{-33}$ cm can grow to the size of the recombination sky if it begins to grow at a temperature of order $10^{33}$ degrees.

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P. Mannheim
Thu, 29 Dec 22
10/47

Comments: 16 pages

Running and running of the running of the scalar spectral index in warm inflation [CEA]

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http://arxiv.org/abs/2212.13914


Next generation of cosmological observations are expected to improve the measurements of several quantities connected to the primordial inflation in the early Universe. These quantities include for example improved measurements for the spectral index of the scalar curvature of the primordial power spectrum and to also bring a better understanding on the scaling dependence of the primordial spectrum. This includes the running of the tilt and, possibly, also the running of the running. In this paper, we investigate the possibility of generating large runnings in the context of warm inflation. Useful analytical expressions for the runnings are derived in the context of warm inflation in the strong dissipation regime. The results are compared to and discussed for some well motivated primordial inflaton potentials that have recently been of interest in the literature.

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S. Das and R. Ramos
Thu, 29 Dec 22
22/47

Comments: 10 pages, double column, 0 figures

Potential signature of a quadrupolar Hubble expansion in Pantheon+ supernovae [CEA]

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http://arxiv.org/abs/2212.13569


The assumption of isotropy — that the Universe looks the same in all directions on large scales — is fundamental to the standard cosmological model. This model forms the building blocks of essentially all of our cosmological knowledge to date. It is therefore critical to empirically test in which regimes its core assumptions hold. Anisotropies in the cosmic expansion are expected on small scales due to nonlinear structures in the late Universe, however, the extent to which these anisotropies might impact our low-redshift observations remains to be fully tested. In this paper, we use fully general relativistic simulations to calculate the expected local anisotropic expansion and identify the dominant multipoles in cosmological parameters to be the quadrupole in the Hubble parameter and the dipole in the deceleration parameter. We constrain these multipoles simultaneously in the new Pantheon+ supernova compilation. The fiducial analysis is done in the rest frame of the CMB with peculiar velocity corrections. Under the fiducial range of redshifts in the Hubble flow sample, we find a $\sim 2\sigma$ deviation from isotropy. We constrain the eigenvalues of the quadrupole in the Hubble parameter to be $\lambda_1 =0.021\pm{ 0.011}$ and $ {\lambda_2= 3.15\times 10^{-5}}\pm 0.012$ and place a $1\sigma$ upper limit on its amplitude of $2.88\%$. We find no significant dipole in the deceleration parameter, finding constraints of $q_{\rm dip} = 4.5^{+1.9}{-5.4}$. However, in the rest frame of the CMB without corrections, we find $ q{ \rm dip} = 9.6^{+4.0}_{-6.9}$, a $>2\sigma$ positive amplitude. We also investigate the impact of these anisotropies on the Hubble tension. We find a maximal shift of $0.30$ km s$^{-1}$ Mpc$^{-1}$ in the monopole of the Hubble parameter and conclude that local anisotropies are unlikely to fully explain the observed tension.

Read this paper on arXiv…

J. Cowell, S. Dhawan and H. Macpherson
Thu, 29 Dec 22
34/47

Comments: 12 pages, to be submitted to MNRAS

On the Schwarzschild-de Sitter metric of nonlocal de Sitter gravity [CL]

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http://arxiv.org/abs/2212.13896


Earlier constructed a simple nonlocal de Sitter gravity model has a cosmological solution in a very good agreement with astronomical observations. In this paper, we continue the investigation of the nonlocal de Sitter model of gravity, focusing on finding an appropriate solution for the Schwarzschild-de Sitter metric. We succeeded to solve the equations of motion in a certain approximation. The obtained approximate solution is of particular interest for examining the possible role of non-local de Sitter gravity in describing the effects in galactic dynamics that are usually attributed to dark matter.

Read this paper on arXiv…

I. Dimitrijevic, B. Dragovich, Z. Rakic, et. al.
Thu, 29 Dec 22
38/47

Comments: 10 pages

Bouncing Cosmology in VCDM [CL]

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http://arxiv.org/abs/2212.13561


We construct an asymmetric bouncing scenario within the VCDM model, a modified gravity theory with two local physical degrees of freedom. The scenario is exempt of any ghost or gradient instability, and avoids any singularity problem, ad-hoc matching conditions or anisotropic stress issue (BKL instability). It moreover succeeds in generating the cosmological perturbations compatible with the observations. The scalar spectral index can be adapted by the choice of the equation of state of the matter sector and the form of the VCDM potential leading to an almost scale-invariant power spectrum. Satisfying the CMB bounds on the tensor-to-scalar ratio leads to a blue tensor spectrum.

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A. Ganz, P. Martens, S. Mukohyama, et. al.
Thu, 29 Dec 22
39/47

Comments: 14 pages, 8 figures

Weak Gravitational Lensing of Schwarzschild and Charged Black Holes Embedded in Perfect Fluid Dark Matter Halo [CL]

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http://arxiv.org/abs/2212.13311


The dark matter and dark energy dominate the behavior of our universe. The unknown dark matter usually forms halos in large number of galaxies. Properties of dark matter halo can be revealed and understood from the gravitational lensing observations. In this work, a comprehensive study on the weak gravitational lensing of black hole embedded in dark matter halos is presented. To effectively model the supermassive black hole in galaxy center (which is surrounded by dark matter halo) in a simple way, we use the Schwarzschild black hole and charged Reissner-Nordstr\”om black hole embedded in a perfect fluid dark matter halo. In the present work, several key quantities in weak gravitational lensing (gravitational deflection angle of light, photon sphere, black hole shadow radius, gravitational lens equation and Einstein ring) are calculated and analyzed analytically and numerically. The results in our work indicate that the dark matter can greatly influence the gravitational lensing of central black holes.

Read this paper on arXiv…

C. Qiao and M. Zhou
Thu, 29 Dec 22
42/47

Comments: 20 pages, 10 figures

The effective Equation of State in Palatini $f(R)$ cosmology [CL]

Posted on by

http://arxiv.org/abs/2212.13825


We investigate how the cosmological Equation of State can be used for scrutinizing extended theories of gravity, in particular, the Palatini $f(R)$ gravity. Specifically, the approach consists, at first, in investigating the effective Equation of State produced by a given model. Then, the inverse problem can also be considered in view of determining which models are compatible with a given effective Equation of State. We consider and solve some cases and show that, for example, power-law models are (the only models) capable of transforming barotropic Equations of State into effective barotropic ones. Moreover, the form of Equation of State is preserved (only) for $f(R)=R$, as expected. In this perspective, modified Equations of State are a feature capable of distinguishing Extended Gravity with respect to General Relativity. We also investigate quadratic and non-homogeneous effective Equations of State showing, in particular, that they contain the Starobinsky model and other ones.

Read this paper on arXiv…

S. S.Camera, S. S.Capozziello, L. L.Fatibene, et. al.
Thu, 29 Dec 22
40/47

Comments: 19 pages

On the Schwarzschild-de Sitter metric of nonlocal de Sitter gravity [CL]

Posted on by

http://arxiv.org/abs/2212.13896


Earlier constructed a simple nonlocal de Sitter gravity model has a cosmological solution in a very good agreement with astronomical observations. In this paper, we continue the investigation of the nonlocal de Sitter model of gravity, focusing on finding an appropriate solution for the Schwarzschild-de Sitter metric. We succeeded to solve the equations of motion in a certain approximation. The obtained approximate solution is of particular interest for examining the possible role of non-local de Sitter gravity in describing the effects in galactic dynamics that are usually attributed to dark matter.

Read this paper on arXiv…

I. Dimitrijevic, B. Dragovich, Z. Rakic, et. al.
Thu, 29 Dec 22
41/47

Comments: 10 pages

First statistical measurement of the Hubble constant using unlocalized fast radio bursts [CEA]

Posted on by

http://arxiv.org/abs/2212.13433


Fast radio bursts (FRBs) can be used to measure the Hubble constant by employing the Macquart relation. However, at present, only a small number of FRB events are localized to their host galaxies with known redshifts. In this paper, we develop a Bayesian method to statistically measure the Hubble constant using unlocalized FRBs and galaxy catalog data, which makes it possible to constrain cosmological parameters by using a large number of FRB data without known redshift information. Using the six FRB events observed by ASKAP combined with the big bang nucleosynthesis result, we obtain $H_0=71.7^{+8.8}{-7.4}$ km s$^{-1}$ Mpc$^{-1}$ in the simulation-based case and $H_0=71.5^{+10.0}{-8.1}$ km s$^{-1}$ Mpc$^{-1}$ in the observation-based case ($68\%$ highest-density interval), assuming different host galaxy population parameters. We also estimate that in the next few years, using thousands of FRBs could achieve a $3\%$ precision on the random error of the Hubble constant.

Read this paper on arXiv…

Z. Zhao, J. Zhang, Y. Li, et. al.
Thu, 29 Dec 22
43/47

Comments: 9 pages, 3 figures

Weak Gravitational Lensing of Schwarzschild and Charged Black Holes Embedded in Perfect Fluid Dark Matter Halo [CL]

Posted on by

http://arxiv.org/abs/2212.13311


The dark matter and dark energy dominate the behavior of our universe. The unknown dark matter usually forms halos in large number of galaxies. Properties of dark matter halo can be revealed and understood from the gravitational lensing observations. In this work, a comprehensive study on the weak gravitational lensing of black hole embedded in dark matter halos is presented. To effectively model the supermassive black hole in galaxy center (which is surrounded by dark matter halo) in a simple way, we use the Schwarzschild black hole and charged Reissner-Nordstr\”om black hole embedded in a perfect fluid dark matter halo. In the present work, several key quantities in weak gravitational lensing (gravitational deflection angle of light, photon sphere, black hole shadow radius, gravitational lens equation and Einstein ring) are calculated and analyzed analytically and numerically. The results in our work indicate that the dark matter can greatly influence the gravitational lensing of central black holes.

Read this paper on arXiv…

C. Qiao and M. Zhou
Thu, 29 Dec 22
45/47

Comments: 20 pages, 10 figures

The Effective Fluid approach for Modified Gravity and its applications [CEA]

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http://arxiv.org/abs/2212.12768


In this review we briefly summarize the so-called effective fluid approach, which is a compact framework that can be used to describe a plethora of different modified gravity models as general relativity (GR) and a dark energy (DE) fluid. This approach, which is complementary to the cosmological effective field theory, has several benefits as it allows for the easier inclusion of most modified gravity models into the state-of-the-art Boltzmann codes, that are typically hard-coded for GR and DE. Furthermore, it can also provide theoretical insights into their behavior, since in linear perturbation theory it is easy to derive physically motivated quantities such as the DE anisotropic stress or the DE sound speed. We also present some explicit applications of the effective fluid approach with $f(R)$, Horndeski and Scalar-Vector-Tensor models, namely how this approach can be used to easily solve the perturbation equations and incorporate the aforementioned modified gravity models into Boltzmann codes so as to obtain cosmological constraints using Monte Carlo analyses.

Read this paper on arXiv…

S. Nesseris
Tue, 27 Dec 22
15/30

Comments: 25 pages, 4 figures. Invited review for the special issue on “Modified Gravity Approaches to the Tensions of LCDM”, based on 1811.02469, 1904.06294 and 2206.02895

The causality road from dynamical triangulations to quantum gravity that describes our Universe [CL]

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http://arxiv.org/abs/2212.13109


It is shown how one, guided by causality, starting from so-called dynamical triangulations, is led to a candidate of quantum gravity that describes our Universe. This theory is based on W- and Jordan algebras. It explains how our Universe was created, how cosmic inflation began and ended, how the topology and the geometry of our Universe was formed, and what was the origin of Big Bang energy. The theory also leads to a modified Friedmann equation which explains the present accelerating expansion of our Universe without appealing to the cosmological constant.

Read this paper on arXiv…

Y. Watabiki
Tue, 27 Dec 22
17/30

Comments: This is a contribution to the Handbook of Quantum Gravity which will be published in 2023. It will appear as a chapter in the section of the handbook denoted “Causal Dynamical Triangulations”

Cosmography with bright and Love sirens [CL]

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http://arxiv.org/abs/2212.13183


Precision cosmology is crucial to understand the different energy components in the Universe and their evolution through cosmic time. Gravitational wave sources are standard sirens that can accurately map out distances in the Universe. Together with the source redshift information, we can then probe the expansion history of the Universe. We explore the capabilities of various gravitational-wave detector networks to constrain different cosmological models while employing separate waveform models for inspiral and post-merger part of the gravitational wave signal from equal mass binary neutron stars. We consider two different avenues to measure the redshift of a gravitational-wave source: first, we examine an electromagnetic measurement of the redshift via either a kilonova or a gamma ray burst detection following a binary neutron star merger (the electromagnetic counterpart method); second, we estimate the redshift from the gravitational-wave signal itself from the adiabatic tides between the component stars characterized by the tidal Love number, to provide a second mass-scale and break the mass-redshift degeneracy (the counterpart-less method). We find that the electromagnetic counterpart method is better suited to measure the Hubble constant while the counterpart-less method places more stringent bounds on other cosmological parameters. In the era of next-generation gravitational-wave detector networks, both methods achieve sub-percent measurement of the Hubble constant $H_0$ after one year of observations. The dark matter energy density parameter $\Omega_{\rm M}$ in the $\Lambda$CDM model can be measured at percent-level precision using the counterpart method, whereas the counterpart-less method achieves sub-percent precision. We, however, do not find the postmerger signal to contribute significantly to these precision measurements.

Read this paper on arXiv…

A. Dhani, S. Borhanian, A. Gupta, et. al.
Tue, 27 Dec 22
21/30

Comments: N/A

Dark energy and matter interacting scenario can relieve $H_0$ and $S_8$ tensions [CEA]

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http://arxiv.org/abs/2212.13146


In this work, we consider a new cosmological model (named $\tilde\Lambda$CDM) in which the vacuum energy interacts with matter and radiation, and test this model using the current cosmological observations. We find that this model can significantly relieve the $H_0$ tension, and at the same time it can also slightly reduce the $S_8$ tension, which cannot be easily observed in other cosmological models. Using the CMB+BAO+SN (CBS) data to constrain the model, we obtain the results of $H_0=70.6^{+1.4}_{-1.7}~\rm{km~s^{-1} Mpc^{-1}}$ and $S_8=0.820\pm 0.011$, and thus the $H_0$ and $S_8$ tensions are relieved to $1.28\sigma$ and $2.67\sigma$, respectively. However, in this case the $\tilde\Lambda$CDM model is not favored by the data, compared with $\Lambda$CDM. We find that when the $H_0$ and $S_8$ data are added into the data combination, the situation is significantly improved. In the CBS+$H_0$ case, we obtain the result of $H_0=72.2\pm 1.2$ ${\rm km~s^{-1}~Mpc^{-1}}$, which relieves the $H_0$ tension to $0.53\sigma$, and in this case the model is favored over $\Lambda$CDM. In the CBS+$H_0$+$S_8$ case, we get a synthetically best situation, $H_0=71.9\pm 1.1$ ${\rm km~s^{-1}~Mpc^{-1}}$ and $S_8=0.8071\pm 0.0099$, in which the $H_0$ and $S_8$ tensions are relived to $0.75\sigma$ and $2.09\sigma$, respectively. In this case, the model is most favored by the data. Therefore, such a cosmological model can greatly relieve the $H_0$ tension, and at the same time it can also effectively alleviate the $S_8$ tension.

Read this paper on arXiv…

L. Gao, S. Xue and X. Zhang
Tue, 27 Dec 22
26/30

Comments: 7 pages, 4 figures

The Effective Fluid approach for Modified Gravity and its applications [CEA]

Posted on by

http://arxiv.org/abs/2212.12768


In this review we briefly summarize the so-called effective fluid approach, which is a compact framework that can be used to describe a plethora of different modified gravity models as general relativity (GR) and a dark energy (DE) fluid. This approach, which is complementary to the cosmological effective field theory, has several benefits as it allows for the easier inclusion of most modified gravity models into the state-of-the-art Boltzmann codes, that are typically hard-coded for GR and DE. Furthermore, it can also provide theoretical insights into their behavior, since in linear perturbation theory it is easy to derive physically motivated quantities such as the DE anisotropic stress or the DE sound speed. We also present some explicit applications of the effective fluid approach with $f(R)$, Horndeski and Scalar-Vector-Tensor models, namely how this approach can be used to easily solve the perturbation equations and incorporate the aforementioned modified gravity models into Boltzmann codes so as to obtain cosmological constraints using Monte Carlo analyses.

Read this paper on arXiv…

S. Nesseris
Tue, 27 Dec 22
9/30

Comments: 25 pages, 4 figures. Invited review for the special issue on “Modified Gravity Approaches to the Tensions of LCDM”, based on 1811.02469, 1904.06294 and 2206.02895

Dark energy and matter interacting scenario can relieve $H_0$ and $S_8$ tensions [CEA]

Posted on by

http://arxiv.org/abs/2212.13146


In this work, we consider a new cosmological model (named $\tilde\Lambda$CDM) in which the vacuum energy interacts with matter and radiation, and test this model using the current cosmological observations. We find that this model can significantly relieve the $H_0$ tension, and at the same time it can also slightly reduce the $S_8$ tension, which cannot be easily observed in other cosmological models. Using the CMB+BAO+SN (CBS) data to constrain the model, we obtain the results of $H_0=70.6^{+1.4}_{-1.7}~\rm{km~s^{-1} Mpc^{-1}}$ and $S_8=0.820\pm 0.011$, and thus the $H_0$ and $S_8$ tensions are relieved to $1.28\sigma$ and $2.67\sigma$, respectively. However, in this case the $\tilde\Lambda$CDM model is not favored by the data, compared with $\Lambda$CDM. We find that when the $H_0$ and $S_8$ data are added into the data combination, the situation is significantly improved. In the CBS+$H_0$ case, we obtain the result of $H_0=72.2\pm 1.2$ ${\rm km~s^{-1}~Mpc^{-1}}$, which relieves the $H_0$ tension to $0.53\sigma$, and in this case the model is favored over $\Lambda$CDM. In the CBS+$H_0$+$S_8$ case, we get a synthetically best situation, $H_0=71.9\pm 1.1$ ${\rm km~s^{-1}~Mpc^{-1}}$ and $S_8=0.8071\pm 0.0099$, in which the $H_0$ and $S_8$ tensions are relived to $0.75\sigma$ and $2.09\sigma$, respectively. In this case, the model is most favored by the data. Therefore, such a cosmological model can greatly relieve the $H_0$ tension, and at the same time it can also effectively alleviate the $S_8$ tension.

Read this paper on arXiv…

L. Gao, S. Xue and X. Zhang
Tue, 27 Dec 22
13/30

Comments: 7 pages, 4 figures

Cosmography with bright and Love sirens [CL]

Posted on by

http://arxiv.org/abs/2212.13183


Precision cosmology is crucial to understand the different energy components in the Universe and their evolution through cosmic time. Gravitational wave sources are standard sirens that can accurately map out distances in the Universe. Together with the source redshift information, we can then probe the expansion history of the Universe. We explore the capabilities of various gravitational-wave detector networks to constrain different cosmological models while employing separate waveform models for inspiral and post-merger part of the gravitational wave signal from equal mass binary neutron stars. We consider two different avenues to measure the redshift of a gravitational-wave source: first, we examine an electromagnetic measurement of the redshift via either a kilonova or a gamma ray burst detection following a binary neutron star merger (the electromagnetic counterpart method); second, we estimate the redshift from the gravitational-wave signal itself from the adiabatic tides between the component stars characterized by the tidal Love number, to provide a second mass-scale and break the mass-redshift degeneracy (the counterpart-less method). We find that the electromagnetic counterpart method is better suited to measure the Hubble constant while the counterpart-less method places more stringent bounds on other cosmological parameters. In the era of next-generation gravitational-wave detector networks, both methods achieve sub-percent measurement of the Hubble constant $H_0$ after one year of observations. The dark matter energy density parameter $\Omega_{\rm M}$ in the $\Lambda$CDM model can be measured at percent-level precision using the counterpart method, whereas the counterpart-less method achieves sub-percent precision. We, however, do not find the postmerger signal to contribute significantly to these precision measurements.

Read this paper on arXiv…

A. Dhani, S. Borhanian, A. Gupta, et. al.
Tue, 27 Dec 22
16/30

Comments: N/A

The causality road from dynamical triangulations to quantum gravity that describes our Universe [CL]

Posted on by

http://arxiv.org/abs/2212.13109


It is shown how one, guided by causality, starting from so-called dynamical triangulations, is led to a candidate of quantum gravity that describes our Universe. This theory is based on W- and Jordan algebras. It explains how our Universe was created, how cosmic inflation began and ended, how the topology and the geometry of our Universe was formed, and what was the origin of Big Bang energy. The theory also leads to a modified Friedmann equation which explains the present accelerating expansion of our Universe without appealing to the cosmological constant.

Read this paper on arXiv…

Y. Watabiki
Tue, 27 Dec 22
27/30

Comments: This is a contribution to the Handbook of Quantum Gravity which will be published in 2023. It will appear as a chapter in the section of the handbook denoted “Causal Dynamical Triangulations”

Building cubic gravity with healthy and viable scalar and tensor perturbations [CL]

Posted on by

http://arxiv.org/abs/2212.12494


We investigate the conditions under which cubic gravity is healthy and viable at the perturbation level. We perform a detailed analysis of the scalar and tensor perturbations. After showing that no instabilities appear, we impose the requirement that the two scalar potentials, whose ratio is the post-Newtonian parameter $\gamma$, should deviate only minimally form general relativity. Additionally, concerning the tensor perturbations we impose satisfaction of the LIGO-VIRGO and Fermi Gamma-ray Burst observations, and thus we result to a gravitational-wave equation with gravitational-wave speed equal to the speed of light, and where the only deviation from general relativity appears in the dispersion relation. Furthermore, we show that cubic gravity exhibits an effective Newton’s constant that depends on the model parameter, on the background evolution, and on the wavenumber scale. Hence, by requiring its deviation from the standard Newton’s constant to be within observational bounds we extract the constraints on the single coupling parameter $\beta$.

Read this paper on arXiv…

P. Asimakis, S. Basilakos and E. Saridakis
Mon, 26 Dec 22
4/39

Comments: 9 pages, 2 figures

Dropping Anchor: Understanding the Populations of Binary Black Holes with Random and Aligned Spin Orientations [HEAP]

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http://arxiv.org/abs/2212.12113


The relative spin orientations of black holes (BHs) in binaries encode their evolutionary history: BHs assembled dynamically should have isotropically distributed spins, while spins of the BHs originating in the field should be aligned with the orbital angular momentum. In this article, we introduce a simple population model for these dynamical and field binaries that uses spin orientations as an anchor to disentangle these two evolutionary channels. We then analyze binary BH mergers in the Third Gravitational-Wave Transient Catalog (GWTC-3) and ask whether BHs from the isotropic-spin population possess different distributions of mass ratio, spin magnitudes, or redshifts from the preferentially-aligned-spin population. We find no compelling evidence that binary BHs in GWTC-3 have different source-property distributions depending on their spin alignment, but we do find that the dynamical and field channels cannot both have mass-ratio distributions that strongly favor equal masses. We give an example of how this can be used to provide insights into the various processes that drive these BHs to merge. We also find that the current detections are insufficient in extracting differences in spin magnitude or redshift distributions of isotropic and aligned spin populations.

Read this paper on arXiv…

V. Baibhav, Z. Doctor and V. Kalogera
Mon, 26 Dec 22
6/39

Comments: 15 pages, 5 figures

Beyond the Born rule in quantum gravity [CL]

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http://arxiv.org/abs/2212.12175


We have recently developed a new understanding of probability in quantum gravity. In this paper we provide an overview of this new approach and its implications. Adopting the de Broglie-Bohm pilot-wave formulation of quantum physics, we argue that there is no Born rule at the fundamental level of quantum gravity with a non-normalisable Wheeler-DeWitt wave functional $\Psi$. Instead the universe is in a perpetual state of quantum nonequilibrium with a probability density $P\neq\left\vert \Psi\right\vert ^{2}$. Dynamical relaxation to the Born rule can occur only after the early universe has emerged into a semiclassical or Schr\”{o}dinger approximation, with a time-dependent and normalisable wave functional $\psi$, for non-gravitational systems on a classical spacetime background. In that regime the probability density $\rho$ can relax towards $\left\vert \psi\right\vert ^{2}$ (on a coarse-grained level). Thus the pilot-wave theory of gravitation supports the hypothesis of primordial quantum nonequilibrium, with relaxation to the Born rule taking place soon after the big bang. We also show that quantum-gravitational corrections to the Schr\”{o}dinger approximation allow quantum nonequilibrium $\rho\neq\left\vert \psi\right\vert ^{2}$ to be created from a prior equilibrium ($\rho=\left\vert \psi\right\vert ^{2}$) state. Such effects are very tiny and difficult to observe in practice.

Read this paper on arXiv…

A. Valentini
Mon, 26 Dec 22
12/39

Comments: 39 pages. For special issue of Foundations of Physics, ‘Pilot-wave and beyond: Louis de Broglie and David Bohm’s quest for a quantum ontology’, ed. A. Drezet

Dynamics of dark energy in a scalar-vector-torsion theory [CL]

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http://arxiv.org/abs/2212.12071


We study the cosmological dynamics of dark energy in a scalar-vector-torsion theory. The vector field is described by the cosmic triad and the scalar field is of the quintessence type with non-minimal coupling to gravity. The coupling to gravity is introduced through the interaction between the scalar field and torsion, where torsion is defined in the context of teleparallel gravity. We derive the full set of field equations for the Friedmann-Lema\^{i}tre-Robertson-Walker space-time background and obtain the associated autonomous system. We obtain the critical points and their stability conditions, along with the cosmological properties of them. Thus, we show that the thermal history of the universe is successfully reproduced. Furthermore, new scaling solutions in which the scalar and vector field densities scale in the same way as the radiation and matter background fluids have been found. Finally, we also show that there exist new attractor fixed points whose nature is mainly vectorial, and which can explain the current accelerated expansion and therefore the dark energy-domination.

Read this paper on arXiv…

M. Gonzalez-Espinoza, G. Otalora, Y. Leyva, et. al.
Mon, 26 Dec 22
19/39

Comments: N/A

The influence of laser relative intensity noise in the Laser Interferometer Space Antenna [CL]

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http://arxiv.org/abs/2212.12052


LISA is an upcoming ESA mission that will detect gravitational waves in space by interferometrically measuring the separation between free-falling test masses at picometer precision. To reach the desired performance, LISA will employ the noise reduction technique time-delay interferometry (TDI), in which multiple raw interferometric readouts are time shifted and combined into the final scientific observables. Evaluating the performance in terms of these TDI variables requires careful tracking of how different noise sources propagate through TDI, as noise correlations might affect the performance in unexpected ways. One example of such potentially correlated noise is the relative intensity noise (RIN) of the six lasers aboard the three LISA satellites, which will couple into the interferometric phase measurements. In this article, we calculate the expected RIN levels based on the current mission architecture and the envisaged mitigation strategies. We find that strict requirements on the technical design reduce the effect from approximately 8.7 pm/rtHz per inter-spacecraft interferometer to that of a much lower sub-1 pm/rtHz noise, with typical characteristics of an uncorrelated readout noise after TDI. Our investigations underline the importance of sufficient balanced detection of the interferometric measurements.

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L. Wissel, O. Hartwig, J. Bayle, et. al.
Mon, 26 Dec 22
23/39

Comments: 15 pages, 10 figures, 2 tables

Some disquisitions on cosmological 2-form dualities [CL]

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http://arxiv.org/abs/2212.12427


In this work we study different aspect of self-interacting 2-form fields with special emphasis in their cosmological applications. We provide the explicit construction of how massless 2-forms are compatible with the cosmological principle without resorting to the dual scalar field formulation. In terms of the 2-form, the residual Euclidean group is non-trivially realised by means of a combination of external spatial translations and internal gauge transformations. After presenting the general discussion of the dualities in cosmological scenarios, we analyse particular examples for some singular models and discuss in some detail the dual descriptions of the DBI, the cuscuton and the ghost condensate as well as the role of the duality in the effective field theories of cosmological perturbations. We then proceed to analysing scenarios with several self-interacting massless 2-forms and we show that they naturally provide the dual description of a solid. We then show how the perfect fluid and superfluids can be obtained by taking the appropriate limits in the dual formulations. We finally consider the case of massive 2-forms and their duals and briefly discuss their potential signatures in gravitational waves astronomy.

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K. Aoki, J. Jiménez and D. Figueruelo
Mon, 26 Dec 22
29/39

Comments: 48 pages

Doppler effect in TianQin time-delay interferometry [CL]

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http://arxiv.org/abs/2212.11437


The current design of space-based gravitational wave detectors utilizes heterodyne laser interferometry in inter-satellite science measurements. Frequency variations of the heterodyne beatnotes are predominantly caused by the Doppler effect from relative satellite motion along lines of sight. Generally considered to be outside the measurement band, the Doppler effect appears to have been largely overlooked in literature on numerical simulations of time-delay interferometry (TDI). However, the potential impact on the effectiveness of TDI should be assessed. The issue is particularly relevant to TianQin that features geocentric orbits, because of strong gravity disturbances from the Earth-Moon system at $<1\times 10^{-4}$ Hz. In this paper, based on high-precision orbital data obtained from detailed gravity field modeling, we incorporate the Doppler shift in the generation of TianQin’s beatnote phase signals. To remove the large-scale Doppler phase drift at $<1\times 10^{-4}$ Hz, we develop a high-performance high-pass filter and consider two possible processing sequences, i.e., applying the filter before or after TDI combinations. Our simulation results favor the former and demonstrate successful removal of the low-frequency gravity disturbances for TianQin without degrading the TDI performance, assuming 10 m pseudo-ranging uncertainty. The filtering scheme can be used in developing the initial noise-reduction pipeline for TianQin.

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L. Zheng, S. Yang and X. Zhang
Fri, 23 Dec 22
10/58

Comments: 9 pages, 11 figures

Gravitational wave lensing as a probe of halo properties and dark matter [CEA]

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http://arxiv.org/abs/2212.11960


Just like light, gravitational waves (GWs) are deflected and magnified by gravitational fields as they propagate through the Universe. However, their low frequency, phase coherence and feeble coupling to matter allow for distinct lensing phenomena, such as diffraction and central images, that are challenging to observe through electromagnetic sources. Here we explore how these phenomena can be used to probe features of gravitational lenses. We focus on two variants of the singular isothermal sphere, with 1) a variable slope of the matter density and 2) a central core. We describe the imprints of these features in the wave- and geometric-optics regimes, including the prospect of detecting central images. We forecast the capacity of LISA and advanced LIGO to study strongly lensed signals and measure the projected lens mass, impact parameter and slope or core size. A broad range of lens masses allows all parameters to be measured with precision up to $\sim 1/{\rm SNR}$, despite large degeneracies. Thanks to wave-optics corrections, all parameters can be measured, even when no central image forms. Although GWs are sensitive to projected quantities, we compute the probability distribution of lens redshift, virial mass and projection scale given a cosmology. As an application, we consider the prospect of constraining self-interacting and ultra-light dark matter, showing the regions of parameter space accessible to strongly-lensed GWs. The distinct GW signatures will enable novel probes of fundamental physics and astrophysics, including the properties of dark matter and the central regions of galactic halos.

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G. Tambalo, M. Zumalacárregui, L. Dai, et. al.
Fri, 23 Dec 22
11/58

Comments: 41 pages, 27 figures

Oscillating cosmic evolution and constraints on big bang nucleosynthesis in the extended Starobinsky model [CEA]

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http://arxiv.org/abs/2212.11487


We investigate the cosmic evolutions in the extended Starobinsky model (eSM) obtained by adding one R ab R ab term to the Starobinsky model. We discuss the possibility of various forms of cosmic evolution with a special focus on the radiation-dominated era (RDE). Using simple assumptions, a second-order non-linear differential equation describing the various cosmic evolutions in the eSM is introduced. By solving this non-linear equation numerically, we show that various forms of cosmic evolution, such as the standard cosmic evolution ($a \propto t^{1/2}$) and a unique oscillating cosmic evolution, are feasible due to the effects of higher-order terms introduced beyond Einstein gravity. Furthermore, we consider big bang nucleosynthesis (BBN), which is the most important observational results in the RDE, to constrain the free parameters of the eSM. The primordial abundances of the light elements, such as $^4$He, D, $^3$He, $^7$Li and $^6$Li by the cosmic evolutions are compared with the most recent observation data. It turns out that most cases of non-standard cosmic evolutions can not easily satisfy these BBN constraints, but a free parameter of the viable models with the oscillating cosmic evolution is shown to have an upper limit by the constraints. In particular, we find that the free parameter is most sensitive to deuterium and $^4$He abundances, which are being precisely measured among other elements. Therefore, more accurate measurements in the near future may enable us to distinguish the eSM from the standard model as well as other models.

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J. Park, C. Yun, M. Cheoun, et. al.
Fri, 23 Dec 22
23/58

Comments: N/A

Non-linear stability of $α'$-corrected Friedmann equations [CL]

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http://arxiv.org/abs/2212.11392


We study the non-linear stability of fixed-point solutions to the $\alpha’$-exact equations from O$(d,d)$ invariant cosmology, with and without matter perturbations. Previous non-linear analysis in the literature is revisited, and its compatibility with known linear perturbation results is shown. Some formal aspects of cosmological perturbations in duality invariant cosmology are discussed, and we show the existence of time-reparameterization invariant variables for perturbations.

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H. Bernardo, J. Chojnacki and V. Comeau
Fri, 23 Dec 22
27/58

Comments: 15 pages

Effect of solar free oscillations on TianQin's range acceleration noise [CL]

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http://arxiv.org/abs/2212.11450


TianQin is a proposed space-based gravitational-wave detector mission to be deployed and operated in high Earth orbits. As a sequel to [Zhang et al. Phys. Rev. D 103, 062001 (2021)], we investigate a type of “orbital noise” in TianQin’s range acceleration that is caused by gravitational perturbation associated with solar free oscillations. Frequencies of such oscillations are typically within TianQin’s measurement band of 0.1 mHz–1 Hz, and the disturbance level needs careful assessment. By using high-precision orbit propagation and adding the Sun’s time-variable oblateness $J_2$ to detailed gravity-field models, we examine the effect in the frequency domain and show that the solar free oscillation noise is expected to be two orders of magnitude lower than the noise requirement on single links and hence has little impact on the mission.

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K. Liu, C. Luo and X. Zhang
Fri, 23 Dec 22
31/58

Comments: 10 pages, 5 figures

Inflation in Palatini quadratic gravity (and beyond) [CL]

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http://arxiv.org/abs/2212.11869


We study single-field slow-roll inflation embedded in a Palatini quadratic $F(R)$ gravity, where the Einstein-Hilbert term has the wrong sign, apparently leading to repulsive gravity. This can be avoided as long as $F'(R)$ and $F”(R)$ stay positive. Surprisingly, consistency of the theory requires the Jordan frame inflaton potential to be unbounded from below. Even more surprisingly, this corresponds to an Einstein frame inflaton potential bounded from below and positive definite. We prove that such a quadratic gravity is an attractor configuration for all the Palatini $F(R)$ that, for infinite curvature, diverge faster than $R^2$.

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C. Dioguardi, A. Racioppi and E. Tomberg
Fri, 23 Dec 22
43/58

Comments: 20 pages, 6 figures

Equilibrium of slowly rotating polytropes in modified theories of gravity [CL]

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http://arxiv.org/abs/2212.11620


A general formalism to find the density profile of a slowly rotating stellar object in modified gravity is presented. We derive a generic Lane-Emden equation and its analytical solution for a wide class of modified theories of gravity.

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S. Chowdhury, P. Banerjee and A. Wojnar
Fri, 23 Dec 22
47/58

Comments: 9 pages

Peaky Production of Light Dark Photon Dark Matter [CL]

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http://arxiv.org/abs/2212.11516


We explore a mechanism to produce a light dark photon dark matter through a coupling between the dark photon field and a spectator scalar field which plays no role in the inflationary expansion of the Universe while rolling down its potential during the inflation. The motion of the spectator field efficiently produces dark photons with large wavelengths which become non-relativistic before the time of matter-radiation equality. The spectrum of the wavelengths is peaky so that the constraint from the isocurvature perturbation can be evaded. The correct relic abundance is then achieved over a wide range of the dark photon mass down to $10^{-13} \ \text{eV}$. Our mechanism favors high-scale inflation models which can be tested in future observations. Furthermore, fluctuations of the dark photon field during inflation produce gravitational waves detectable at future space-based interferometers and/or pulsar timing array experiments.

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Y. Nakai, R. Namba and I. Obata
Fri, 23 Dec 22
54/58

Comments: 27 pages, 6 figures

The formation of $30\,M_\odot$ merging black holes at solar metallicity [HEAP]

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http://arxiv.org/abs/2212.10924


The maximum mass of black holes formed in isolated binaries is determined by stellar winds and the interactions between the binary components. We consider for the first time fully self-consistent detailed stellar structure and binary evolution calculations in population-synthesis models and a new, qualitatively different picture emerges for the formation of black-hole binaries, compared to studies employing rapid population synthesis models. We find merging binary black holes can form with a non-negligible rate ($\sim 4\times10^{-7}\,M_\odot^{-1}$) at solar metallicity. Their progenitor stars with initial masses $\gtrsim 50\,M_\odot$ do not expand to supergiant radii, mostly avoiding significant dust-driven or luminous blue variable winds. Overall, the progenitor stars lose less mass in stellar winds, resulting in black holes as massive as $\sim 30\,M_\odot$, and, approximately half of them avoid a mass-transfer episode before forming the first-born black hole. Finally, binaries with initial periods of a few days, some of which may undergo episodes of Roche-lobe overflow mass transfer, result in mildly spinning first-born black holes, $\chi_\mathrm{BH1} \lesssim 0.2$, assuming efficient angular-momentum transport.

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S. Bavera, T. Fragos, E. Zapartas, et. al.
Thu, 22 Dec 22
14/59

Comments: 14 pages, 6 figures, manuscript submitted for publication

Nucleosynthesis in Outflows from Black Hole-Neutron Star Merger Disks With Full GR$ν$RMHD [HEAP]

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http://arxiv.org/abs/2212.10691


Along with binary neutron star mergers, the in-spiral and merger of a black hole and a neutron star is a predicted site of $r$-process nucleosynthesis and associated kilonovae. For the right mass ratio, very large amounts of neutron rich material may become unbound from the post-merger accretion disk. We simulate a suite of four post-merger disks with full-transport general relativistic neutrino radiation magnetohydrodynamics. We find that the outflows from these disks are very close to the threshold conditions for robust $r$-process nucleosynthesis. For these conditions, the detailed properties of the outflow determine whether a full $r$-process can or cannot occur, implying that a wide range of observable phenomena are possible. We show that on average the disk outflow lanthanide fraction is suppressed relative to the solar isotopic pattern. In combination with the dynamical ejecta, these outflows imply a kilonova with both blue and red components.

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S. Curtis, J. Miller, C. Frohlich, et. al.
Thu, 22 Dec 22
15/59

Comments: N/A

Thermalization, Fragmentation and Tidal Disruption: The Complex Galactic Dynamics of Dark Matter Superfluidity [CEA]

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http://arxiv.org/abs/2212.10577


The idea of self-interacting bosonic dark matter capable of exhibiting superfluidity is revisited. We show that the most interesting parameter space of the theory corresponds to fully thermalized dark matter halos. As a result the entire halo undergoes Bose-Einstein condensation due to high degeneracy. Since it is observationally preferable for the dark matter density profile to be similar to cold dark matter in the outskirts of the halo, we argue that the Jeans wavelength must be at least few times shorter than the virial radius. This entails that, upon condensation, a dark matter halo fragments into superfluid clumps. However, we demonstrate that these would-be solitons experience strong tidal disruption and behave as virialized weakly interacting streams. An exception is the central soliton, which can be as large as few tens of kiloparsecs in size without contradicting observational bounds. As a result, in dwarf galaxies, the observed rotation curves can be completely contained within the superfluid soliton. In this case, the dark matter distribution is expected to be strongly sensitive to the baryonic density profile. We argue that the diversity of rotation curves observed for dwarf galaxies is a natural consequence of the superfluid dark matter scenario.

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L. Berezhiani, G. Cintia and J. Khoury
Thu, 22 Dec 22
19/59

Comments: 28+1 pages, 4 figures

Oscillations and tidal deformations of crystallized white dwarfs [SSA]

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http://arxiv.org/abs/2212.11044


Long predicted more than fifty years ago, strong evidence for the existence of crystalline cores inside white dwarfs has recently been obtained by the Gaia space telescope. It is thus important to investigate how a crystalline core may affect the properties and dynamics of white dwarfs. In this paper, we first study the dependence of the frequencies of the fundamental (f), interfacial (i), and shear (s) oscillation modes on the size of the crystalline core. We find that the frequencies of the i- and s-modes depend sensitively on the size of the core, while the frequency of the f-mode is affected only slightly by at most a few percent for our chosen white dwarf models. We next consider the tidal deformability of crystallized white dwarfs and find that the effect of crystallization becomes significant only when the radius of the core is larger than about 70% of the stellar radius. The tidal deformability can change by a few to about 10 percent when a white dwarf becomes fully crystallized. We also show that there exist approximate equation-of-state insensitive relations connecting the mass, moment of inertia, tidal deformability, and f-mode frequency for pure fluid white dwarfs. Depending on the stellar mass and composition, however, these relations can be affected by a few percent when the white dwarf is crystallized. These changes could leave an imprint on the gravitational waves emitted from the late inspiral or merger of white dwarf binaries, which may be detectable by future space-borne gravitational wave detectors.

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Y. Tang and L. Lin
Thu, 22 Dec 22
36/59

Comments: 12 pages, 18 figures

Parameter Estimation of Eccentric Gravitational Waves with Decihertz Observatory and Its Cosmological Implications [CL]

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http://arxiv.org/abs/2212.11131


Eccentricity of compact binaries can improve the parameter estimation of gravitational waves (GWs), which is due to the fact that the multiple harmonics induced by eccentricity can provide more information and break the degeneracy between waveform parameters. In this paper, we first investigate the parameter estimation of eccentric GWs with decihertz observatory. We consider two scenarios for the configuration of DECIGO, i.e., the one cluster of DECIGO with its design sensitivity and B-DECIGO which also has one cluster but with inferior sensitivity as a comparison. We adopt the Fisher matrix to estimate the parameter errors. By mocking up the typical binaries in GWTC-3, we find a nonvanishing eccentricity can significantly improve the estimation for almost all waveform parameters. In particular, the localization of typical binary black holes (BBH) can achieve $\mathcal{O}(10-10^{3.5})$ factors of improvement when the initial eccentricity $e_0=0.4$ at 0.1 Hz. The precise localization of binary neutron stars (BNS) and neutron star–black hole binaries (NSBH), together with the large improvement of localization of BBH from eccentricity in the mid-band, inspire us to construct the catalogs of golden dark sirens whose host galaxies can be uniquely identified. We find that with only one cluster of DECIGO running 1 year in its design sensitivity, hundreds of golden dark BNS, NSBH, and tens of golden dark BBH can be observed. Eccentricity can greatly increase the population of golden dark BBH from $\sim 7~(e_0=0)$ to $\sim 65~(e_0=0.2)$. Such an increase of population of golden dark BBH events can improve the precision of Hubble constant measurement from 2.06\% to 0.68\%, matter density parameter from 64\% to 16\% in $\Lambda$CDM model. Through the phenomenological parameterization of GW propagation, the constraints of modified gravity can be improved from 6.2\% to 1.6\%.

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T. Yang, R. Cai, Z. Cao, et. al.
Thu, 22 Dec 22
38/59

Comments: 28 pages, 23 figures

Numerical-relativity simulation for tidal disruption of white dwarfs by a supermassive black hole [HEAP]

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http://arxiv.org/abs/2212.10891


We study tidal disruption of white dwarfs in elliptic orbits with the eccenticity of $\sim 1/3$–$2/3$ by a non-spinning supermassive black hole of mass $M_{\rm BH}=10^5M_\odot$ in fully general relativistic simulations targeting the extreme mass-ratio inspiral leading eventually to tidal disruption. Numerical-relativity simulations are performed by employing a suitable formulation in which the weak self-gravity of white dwarfs is accurately solved. We reconfirm that tidal disruption occurs for white dwarfs of the typical mass of $\sim 0.6M_\odot$ and radius $\approx 1.2 \times 10^4$\,km near the marginally bound orbit around a non-spinning black hole with $M_{\rm BH}\alt 4\times 10^5M_\odot$.

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A. Lam, M. Shibata and K. Kiuchi
Thu, 22 Dec 22
47/59

Comments: N/A

Generating enhanced parity-violating gravitational waves during inflation with violation of NEC [CL]

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http://arxiv.org/abs/2212.10893


A violation of the null energy condition (NEC) during inflation in a single field inflation model will naturally enhance the amplitude of the parity violation effect (defined by $\Delta\chi$) of inflationary primordial gravitational waves (GWs), provided the inflaton is non-minimally coupled to a gravitational Chern-Simons term. After going through the NEC-violating phase, the universe enters subsequent slow-roll inflation with a higher scale, which results in an enhanced nearly scale-invariant power spectrum (i.e., $P_{\rm T}$) of inflationary primordial GWs in the high-frequency band, while $P_{\rm T}$ remains consistent with observations in the frequency band of the cosmic microwave background. Therefore, the violation of NEC during inflation will amplify the observability (i.e., $P_{\rm T}\cdot\Delta\chi$) of the parity violation effect. For a sufficiently large $P_{\rm T}$, a $\Delta\chi$ as small as a few percent can imprint a significant signal of parity violation in the GWs background, which might be detectable for pulsar timing arrays and space-based detectors in the future.

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Y. Cai
Thu, 22 Dec 22
53/59

Comments: 19 pages, 16 figures

Glimpse of Quantum Gravitons post the Last Scattering Surface [CL]

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http://arxiv.org/abs/2212.09784


In the cosmological settings, Quantum Gravity effects are typically understood to be limited towards very early phase of the universe, namely in the pre-inflationary era, with limited signatures remaining present in the succeeding inflationary era. These signatures also gradually fade away as the universe grows and exits the inflationary era. In the subsequent radiation and matter dominated era quantum gravity is expected to play no significant role. Classicalized primordial perturbations such as the scalar perturbations and the gravitational waves are expected to leave an imprint on CMB anisotropy and its polarization respectively but quantized gravitational waves are not expected to lead to any appreciable observable effects. Apart from cosmology, in other avenues as well, the imprints of quantum character of gravitational waves are typically so subdued that any possible signature gets buried under a huge pile of the noise or effects from other much stronger processes. In this work, we demonstrate that quantum gravity perturbations cause strong observable effects in cosmological settings post the Last Scattering Surface (LSS) more prominently than any other classical or quantum processes. This counter-intuitive effect is facilitated by the fact that the correlators of the gravitational waves {\it grow divergently large in the matter dominated era} unlike any other background fields, leading to an abrupt rise in the processes mediated by correlators of quantum gravitons. The transitions between spherical harmonics states of newly formed hydrogen atom at the LSS, when the universe resides in strong matter dominated era, provides an example of such a process. We further establish that the late time epoch just before the kicking in of the dark energy provides one of the cleanest avenues to study such quantum gravity effects.

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A. Dhanuka and K. Lochan
Wed, 21 Dec 22
6/81

Comments: 12 pages, 1 Figure

E-TEST prototype design report [IMA]

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http://arxiv.org/abs/2212.10083


E-TEST (Einstein Telescope Euregio-Meuse-Rhin Site and Technology) is a project recently funded by the European program Ineterreg Euregio Meuse-Rhine. This program is dedicated to innovative cross boarder activities between Belgium, The Netherlands and Germany. With a total budget of15MC and a consortium of 11 partners from the three countries, the objective of the project is twofold. Firstly, to develop an eco-friendly and non-invasive imaging of the geological conditions as well as the development of an observatory of the underground in the EMR region. Secondly, to develop technologies necessary for 3rd generation gravitational wave detectors. In particular, it is proposed to develop a prototype of large suspended cryogenic silicon mirror, isolated from seismic vibrations at low frequency. The total budget of the project is equally spread over the two activities. The first activity is not discussed at all in this report. The E-TEST prototype will have some key unique features: a silicon mirror of 100 kg, a radiative cooling strategy (non contact), a low-frequency hybrid isolation stage, cryogenic sensors and electronics, a laser and optics at 2 microns, a low thermal noise coating.

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A. Sider, L. Amez-Droz, A. Amorosi, et. al.
Wed, 21 Dec 22
8/81

Comments: N/A

The hypermagnetic power spectra and the phases of Sakharov oscillations [CL]

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http://arxiv.org/abs/2212.10214


If the gauge fields are amplified from the inflationary vacuum, the quantum mechanical initial data correspond to travelling waves that turn asymptotically into standing waves whose phases only depend on the evolution of the gauge coupling. We point out that these gauge analogs of the Sakharov oscillations are exchanged by the duality symmetry and ultimately constrain both the relative scaling of the hypermagnetic power spectra and their final asymptotic values. Unlike the case of the density contrasts in a relativistic plasma, the standing oscillations never develop since they are eventually overdamped by the finite value of the conductivity as soon as the corresponding modes are comparable with the expansion rates after inflation. We show that the late-time value of the magnetic field is not determined at radiation dominance (and in spite of the value of the wavenumber) but it depends on the moment when the wavelengths (comparable with the Mpc) get of the order of the Hubble radius before equality. This means that the magnetogenesis requirements are only relaxed if the post-inflationary expansion rate is slower than radiation but the opposite is true when the plasma expands faster than radiation and the corresponding power spectra are further suppressed. After combining the present findings with the evolution of the gauge coupling we show that these results are consistent with a magnetogenesis scenario where the gauge coupling is always perturbative during the inflationary stage while, in the dual case, the same requirements cannot be satisfied.

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M. Giovannini
Wed, 21 Dec 22
11/81

Comments: 40 pages, 11 figures

Newtonian Fractional-Dimension Gravity and Galaxies without Dark Matter [CL]

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http://arxiv.org/abs/2212.09932


We apply Newtonian Fractional-Dimension Gravity (NFDG), an alternative gravitational model, to some notable cases of galaxies with little or no dark matter. In the case of the ultra-diffuse galaxy AGC 114905, we show that NFDG methods can effectively reproduce the observed rotation curve, by using a variable fractional dimension $D\left (R\right )$ as was done for other galaxies in previous studies. For AGC 114905, we obtain a variable dimension in the range $D \approx 2.2 -3.2$, but our fixed $D =3$ curve can still fit all the experimental data within their error bars. This confirms other studies indicating that the dynamics of this galaxy can be described almost entirely by the baryonic mass distribution alone. However, our NFDG model explains the residual discrepancies without using any dark matter component.
In the case of NGC 1052-DF2, we use an argument based on the NFDG extension of the virial theorem applied to the velocity dispersion of globular clusters showing that, in general, discrepancies between observed and predicted velocity dispersions can be attributed to an overall fractal dimension $D <3$ of the astrophysical structure considered and not to the presence of dark matter. For NGC 1052-DF2 we estimate $D \approx 2.9$, thus confirming that this galaxy almost follows standard Newtonian behavior. We also consider the case of the Bullet Cluster merger (1E0657-56), assumed to be one of the strongest proofs of dark matter existence. A simplified but effective NFDG model of the collision shows that the observed infall velocity of this merger can be explained by a fractional dimension of the system in the range $D \simeq 2.4 -2.5$, again without using any dark matter.

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G. Varieschi
Wed, 21 Dec 22
21/81

Comments: 12 pages, including 3 figures. Sixth paper on NFDG

A novel test of gravity via black hole eikonal correspondence [CL]

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http://arxiv.org/abs/2212.10028


When adopted in black hole spacetimes, geometric-optics approximations imply a mapping between the quasinormal mode (QNM) spectrum of black holes in the eikonal limit and black hole images. In particular, the real part and the imaginary part of eikonal QNM frequencies are associated with the apparent size and the detailed structure of the ring images, respectively. This correspondence could be violated when going beyond general relativity. We propose a novel method to test the eikonal correspondence via the comparison of two sets of observables from a nonrotating black hole, one extracted from QNM spectra and the other from the lensed photon rings on the image plane. Specifically, the photon ring observables robustly capture the information of the black hole spacetime itself regardless of the surrounding emission models. Therefore, the proposed test of eikonal correspondence can be validated in quite broad scenarios.

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C. Chen, Y. Chen, M. Ho, et. al.
Wed, 21 Dec 22
22/81

Comments: 8 pages, 2 figures

Cosmological stability in $f(φ,{\cal G})$ gravity [CL]

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http://arxiv.org/abs/2212.10022


In gravitational theories where a canonical scalar field $\phi$ with a potential $V(\phi)$ is coupled to a Gauss-Bonnet (GB) term ${\cal G}$ with the Lagrangian $f(\phi,{\cal G})$, we study the cosmological stability of tensor and scalar perturbations in the presence of a perfect fluid. We show that, in decelerating cosmological epochs with a positive tensor propagation speed squared, the existence of nonlinear functions of ${\cal G}$ in $f$ always induces Laplacian instability of a dynamical scalar perturbation associated with the GB term. This is also the case for $f({\cal G})$ gravity, where the presence of nonlinear GB functions $f({\cal G})$ is not allowed during the radiation- and matter-dominated epochs. A linearly coupled GB term with $\phi$ of the form $\xi (\phi){\cal G}$ can be consistent with all the stability conditions, provided that the scalar-GB coupling is subdominant to the background cosmological dynamics.

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S. Tsujikawa
Wed, 21 Dec 22
25/81

Comments: 13 pages, no figures

Numerical analysis of quasi-periodic oscillations with spherical spacetimes [CL]

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http://arxiv.org/abs/2212.10186


We numerically test quasi-periodic oscillations using three theoretically-motivated models of spacetime adopting neutron star sources. Then, we compare our findings with a spherically-symmetric spacetime inferred from $F(R)$ gravity, with constant curvature, showing that it fully-degenerates with our previous metrics, that have been adopted in the context of general relativity. To do so, we work out eight neutron stars in low mass X-ray binary systems and consider a Reisser-Nordstr\”{o}m solution plus a de Sitter phase with unspecified sign for the cosmological constant term. In particular, we investigate three hierarchies, \textit{i.e.}, the first dealing with a genuine Schwarzschild spacetime, the second with de Sitter phase whose sign is not fixed \emph{a priori} and, finally, a Reisser-Nordstr\”{o}m spacetime with an additional cosmological constant contribution. We perform Markov chain Monte Carlo analyses, based on the Metropolis-Hastings algorithm, and infer 1–$\sigma$ and 2–$\sigma$ error bars. For all the sources, we find suitable agreement with spherical solutions with non-zero cosmological constant terms, \textit{i.e.}, with either de Sitter or anti-de Sitter solutions. From our findings, we notice that the existence of topological contribution to the net charge, suggested from $F(R)$ extensions of gravity, seems to be disfavored. Finally, we focus on the physics of the cosmological constant term here involved, investigating physical consequences and proposing possible extensions to improve our overall treatments.

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K. Boshkayev, O. Luongo and M. Muccino
Wed, 21 Dec 22
27/81

Comments: 11 pages, 2 tables, 2 figures

Stability of non-degenerate Ricci-type Palatini theories [CL]

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http://arxiv.org/abs/2212.09820


We study the stability of theories where the gravitational action has arbitrary algebraic dependence on the three first traces of the Riemann tensor: the Ricci tensor, the co-Ricci tensor, and the homothetic curvature tensor. We collectively call them Ricci-type tensors. We allow arbitrary coupling to matter. We consider the case when the connection is unconstrained, and the cases when either torsion or non-metricity is assumed to vanish. We find which combinations of Ricci-type tensors lead to new degrees of freedom around Minkowski and FLRW space, and when there are ghosts. None of the theories with new degrees of freedom are healthy, except the previously known case when torsion is zero and the action depends only on the Ricci tensor. We find that projective invariance is not a sufficient condition for a theory to be ghost-free.

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J. Annala and S. Rasanen
Wed, 21 Dec 22
29/81

Comments: 16+5 pages, no figures

A new universal property of cosmological gravitational wave anisotropies [CL]

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http://arxiv.org/abs/2212.10316


The anisotropies of the stochastic gravitational wave background, as produced in the early phases of cosmological evolution, can act as a key probe of the primordial universe particle content. We point out a new universal property of gravitational wave anisotropies of cosmological origin: for adiabatic initial conditions, their angular power spectrum is insensitive to the equation of state of the cosmic fluid driving the expansion before big-bang nucleosynthesis. Any deviation from this universal behaviour points to the presence of non-adiabatic sources of primordial fluctuations. Such scenarios can be tested by gravitational wave detectors operating at a frequency range which is fully complementary to CMB experiments. In this work we prove this general result, and we illustrate its consequences for a representative realisation of initial conditions based on the curvaton scenario. In the case of the simplest curvaton setup, we also find a significant cross-correlation between gravitational wave anisotropies and the CMB temperature fluctuations. There is a fourfold enhancement vis-`{a}-vis the purely adiabatic scenario. We discuss the implications of our findings for identifying the origin of the (cosmological) gravitational wave background when, as is often the case, this cannot be determined solely on the basis of its spectral shape.

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A. Malhotra, E. Dimastrogiovanni, G. Domènech, et. al.
Wed, 21 Dec 22
31/81

Comments: 14 pages, 4 figures

Quasar UV/X-ray relation luminosity distances are shorter than reverberation-measured radius-luminosity relation luminosity distances [CEA]

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http://arxiv.org/abs/2212.10483


We use measurements of 59/58 quasars (QSOs), over a redshift range $0.0041\leq z \leq 1.686$, to do a comparative study of the radius–luminosity ($R-L$) and X-ray$-$UV luminosity ($L_X-L_{UV}$) relations and the implication of these relations for cosmological parameter estimation. By simultaneously determining $R-L$ or $L_X-L_{UV}$ relation parameters and cosmological parameters in six different cosmological models, we find that both $R-L$ and $L_X-L_{UV}$ relations are standardizable but provide only weak cosmological parameter constraints, with $L_X-L_{UV}$ relation data favoring larger current non-relativistic matter density parameter $\Omega_{m0}$ values than $R-L$ relation data and most other available data. We derive $L_X-L_{UV}$ and $R-L$ luminosity distances for each of the sources in the six cosmological models and find that $L_X-L_{UV}$ relation luminosity distances are shorter than $R-L$ relation luminosity distances as well as standard flat $\Lambda$CDM model luminosity distances. This explains why $L_X-L_{UV}$ relation QSO data favor larger $\Omega_{m0}$ values than do $R-L$ relation QSO data or most other cosmological measurements. While our sample size is small and only spans a small $z$ range, these results indicate that more work is needed to determine whether the $L_X-L_{UV}$ relation can be used as a cosmological probe.

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N. Khadka, M. Zajaček, R. Prince, et. al.
Wed, 21 Dec 22
32/81

Comments: 19 pages, 9 figures

Improved detection statistics for non Gaussian gravitational wave stochastic backgrounds [CL]

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http://arxiv.org/abs/2212.10038


In a recent paper we described a novel approach to the detection and parameter estimation of a non\textendash Gaussian stochastic background of gravitational waves. We devised an inference procedure that uses signal realizations and importance sampling to weight integrals appearing in relevant statistical quantities. In particular, we constructed the associated detection statistics: in order to provide robustness against stationary noise uncertainties we proposed a subtraction procedure to remove terms with non–zero expectation values in absence of signal. We characterized the detector statistics performances, and observed that for low to moderate non-Gaussianities it is outperformed by established Gaussian inference schemes. In this work we propose a more careful, robust subtraction procedure: while still using the importance sampling scheme, it does not introduce performance penalties. We provide formal proof of its efficiency and, following closely the approach in our previous paper, we benchmark its performances on the same toy model: the proposed approach performs better than the Gaussian statistics everywhere in the model parameter space, therefore constituting a crucial addition to our framework.

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M. Ballelli, R. Buscicchio, B. Patricelli, et. al.
Wed, 21 Dec 22
35/81

Comments: 9 pages, 5 figures

Using Pulsar Parameter Drifts to Detect Sub-Nanohertz Gravitational Waves [HEAP]

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http://arxiv.org/abs/2212.09751


Gravitational waves with frequencies below 1 nHz are notoriously difficult to detect. With periods exceeding current experimental lifetimes, they induce slow drifts in observables rather than periodic correlations. Observables with well-known intrinsic contributions provide a means to probe this regime. In this work, we demonstrate the viability of using observed pulsar timing parameters to discover such ”ultralow” frequency gravitational waves, presenting two complementary observables for which the systematic shift induced by ultralow-frequency gravitational waves can be extracted. Using existing data for these parameters, we search the ultralow frequency regime for continuous-wave signals, finding a sensitivity near the expected prediction from supermassive black hole mergers. We do not see an excess in the data, setting a limit on the strain of $ 7.1 \times 10 ^{ – 14} $ at 1 nHz with a sensitivity dropping approximately quadratically with frequency until 10 pHz. Our search method opens a new frequency range for gravitational wave detection and has profound implications for astrophysics, cosmology, and particle physics.

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W. DeRocco and J. Dror
Wed, 21 Dec 22
51/81

Comments: 12 pages, 2 figures, 3 appendices

Inflation in Metric-Affine Quadratic Gravity [CL]

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http://arxiv.org/abs/2212.09896


In the general framework of Metric-Affine theories of gravity, where the metric and the connection are independent variables, we consider actions quadratic in the Ricci scalar curvature and the Holst invariant (the contraction of the Riemann curvature with the Levi-Civita antisymmetric tensor) coupled non-minimally to a scalar field. We study the profile of the equivalent effective metric theory, featuring an extra dynamical pseudoscalar degree of freedom, and show that it reduces to an effective single-field inflationary model. We analyze in detail the inflationary predictions and find that they fall within the latest observational bounds for a wide range of parameters, allowing for an increase in the tensor-to-scalar ratio. The spectral index can either decrease or increase depending on the position in parameter space.

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I. Gialamas and K. Tamvakis
Wed, 21 Dec 22
53/81

Comments: 21 pages, 7 figures, 3 tables

Transverse Doppler effect and parameter estimation of LISA three-body systems [CL]

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http://arxiv.org/abs/2212.09753


Some binary black hole systems potentially observable in LISA could be in orbit around a supermassive black hole (SMBH). The imprint of relativistic three-body effects on the waveform of the binary can be used to estimate all the parameters of the triple system, in particular the mass of the SMBH. We determine the phase shift in the waveform due to the Doppler effect of the SMBH up to second order in velocity, which breaks a well-known exact degeneracy of the lowest-order Doppler effect between the mass of the SMBH and its inclination. We perform several parameter estimations for LISA signals including this additional dephasing in the wave, showing that one can determine accurately all parameters of the three-body system. Our results indicate that one can measure the mass of a $10^8\,$M$_{\odot}$ SMBH with an accuracy better than $\sim 30\%$ (resp. $\sim 15\%$) by monitoring the waveform of a binary system whose period around the SMBH is less 100 yr (resp. 20 yr).

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A. Kuntz and K. Leyde
Wed, 21 Dec 22
55/81

Comments: N/A

Dark photon superradiance: Electrodynamics and multimessenger signals [HEAP]

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http://arxiv.org/abs/2212.09772


We study the electrodynamics of a kinetically mixed dark photon cloud that forms through superradiance around a spinning black hole, and design strategies to search for the resulting multimessenger signals. A dark photon superradiance cloud sources a rotating dark electromagnetic field which, through kinetic mixing, induces a rotating visible electromagnetic field. Standard model charged particles entering this field initiate a transient phase of particle production that populates a plasma inside the cloud and leads to a system which shares qualitative features with a pulsar magnetosphere. We study the electrodynamics of the dark photon cloud with resistive magnetohydrodynamics methods applicable to highly magnetized plasma, adapting techniques from simulations of pulsar magnetospheres. We identify turbulent magnetic field reconnection as the main source of dissipation and electromagnetic emission, and compute the peak luminosity from clouds around solar-mass black holes to be as large as $10^{43}$ erg/s for open dark photon parameter space. The emission is expected to have a significant X-ray component and is potentially periodic, with period set by the dark photon mass. The luminosity is comparable to the brightest X-ray sources in the Universe, allowing for searches at distances of up to hundreds of Mpc with existing telescopes. We discuss observational strategies, including targeted electromagnetic follow-ups of solar-mass black hole mergers and targeted continuous gravitational wave searches of anomalous pulsars.

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N. Siemonsen, C. Mondino, D. Egana-Ugrinovic, et. al.
Wed, 21 Dec 22
70/81

Comments: 55 pages, 27 figures

Equivalence of Active and Passive Gravitational Mass Tested with Lunar Laser Ranging [CL]

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http://arxiv.org/abs/2212.09407


LLR measures the distance between observatories on Earth and retro-reflectors on Moon since 1969. In this paper, we study the possible violation of the equality of passive and active gravitational mass ($m_{a}/m_{p}$), for Aluminium (Al) and Iron (Fe), using LLR data. Our new limit of $3.9\cdot10^{-14}$ is about 100 times better than that of Bartlett and Van Buren [1986] reflecting the benefit of the many years of LLR data.

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V. Singh, J. Müller, L. Biskupek, et. al.
Tue, 20 Dec 22
10/97

Comments: 4 pages, 1 figure

Cosmological gravity probes: connecting recent theoretical developments to forthcoming observations [CEA]

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http://arxiv.org/abs/2212.09094


Since the discovery of the accelerated expansion of the present Universe, significant theoretical developments have been made in the area of modified gravity. In the meantime, cosmological observations have been providing more high-quality data, allowing us to explore gravity on cosmological scales. To bridge the recent theoretical developments and observations, we present an overview of a variety of modified theories of gravity and the cosmological observables in the cosmic microwave background and large-scale structure, supplemented with a summary of predictions for cosmological observables derived from cosmological perturbations and sophisticated numerical studies. We specifically consider scalar-tensor theories in the Horndeski and DHOST family, massive gravity/bigravity, vector-tensor theories, metric-affine gravity, and cuscuton/minimally-modified gravity, and discuss the current status of those theories with emphasis on their physical motivations, validity, appealing features, the level of maturity, and calculability. We conclude that the Horndeski theory is one of the most well-developed theories of modified gravity, although several remaining issues are left for future observations. The paper aims to help to develop strategies for testing gravity with ongoing and forthcoming cosmological observations.

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S. Arai, K. Aoki, Y. Chinone, et. al.
Tue, 20 Dec 22
23/97

Comments: 115 pages, 8 figures

Leptogenesis via Inflaton Mass Terms in Non-Minimally Coupled Inflation [CL]

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http://arxiv.org/abs/2212.09454


We consider a model of baryogenesis based on adding lepton number-violating quadratic mass terms to the inflaton potential of a non-minimally coupled inflation model. The $L$-violating mass terms generate a lepton asymmetry in a complex inflaton field via the mass term Affleck-Dine mechanism, which is transferred to the Standard Model (SM) sector when the inflaton decays to right-handed (RH) neutrinos. The model is minimal in that it requires only the SM sector, RH neutrinos, and a non-minimally coupled inflaton sector. We find that baryon isocurvature fluctuations can be observable in metric inflation but are negligible in Palatini inflation. The model is compatible with reheating temperatures that may be detectable in the observable primordial gravitational waves predicted by metric inflation.

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K. Lloyd-Stubbs and J. McDonald
Tue, 20 Dec 22
30/97

Comments: 18 pages, 6 figures

Eliminating polarization leakage effect for neutral hydrogen intensity mapping with deep learning [IMA]

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http://arxiv.org/abs/2212.08773


The neutral hydrogen (HI) intensity mapping (IM) survey is regarded as a promising approach for cosmic large-scale structure (LSS) studies. A major issue for the HI IM survey is to remove the bright foreground contamination. A key to successfully remove the bright foreground is to well control or eliminate the instrumental effects. In this work, we consider the instrumental effect of polarization leakage and use the U-Net approach, a deep learning-based foreground removal technique, to eliminate the polarization leakage effect.In this method, the principal component analysis (PCA) foreground subtraction is used as a preprocessing step for the U-Net foreground subtraction. Our results show that the additional U-Net processing could either remove the foreground residual after the conservative PCA subtraction or compensate for the signal loss caused by the aggressive PCA preprocessing. Finally, we test the robustness of the U-Net foreground subtraction technique and show that it is still reliable in the case of existing constraint error on HI fluctuation amplitude.

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L. Gao, Y. Li, S. Ni, et. al.
Tue, 20 Dec 22
32/97

Comments: 12 pages, 11 figures

Deviation in stellar trajectory induced by asymmetry in partial tidal disruption [HEAP]

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http://arxiv.org/abs/2212.09122


We study partial tidal disruption and present a quantitative analysis of the orbital dynamics of the remnant self-bound core. We perform smoothed particle hydrodynamical simulations to show that partial disruption of a star due to the tidal field of a black hole leads to a jump in the specific orbital energy and angular momentum of the core. It directly leads to deviation in the core’s trajectory apart from getting a boost in its velocity. Our analysis shows that the variations in the specific orbital energy and angular momentum are higher when the pericentre distance is lower. We conclude that higher mass asymmetry of the two tidal tails increases the magnitude of the trajectory deviations. Our study reveals that observable deviations are only possible when mass ratio $q \lesssim 10^3 $, which indicates the range of intermediate-mass black holes.

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P. Banerjee, D. Garain, S. Chowdhury, et. al.
Tue, 20 Dec 22
33/97

Comments: 15 Pages, 4 figures

Enhancing the use of Galactic neutron stars as physical laboratories with precise astrometry [HEAP]

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http://arxiv.org/abs/2212.08881


The existence of neutron stars was not confirmed until the discovery of pulsars at radio wavelengths in late 1960s. Since then, these highly compact and magnetized objects have been observed across the electromagnetic spectrum, and widely studied. However, lots of the studies related to neutron stars require precise determination of their distances and proper motions. This thesis focuses on high-precision astrometry of neutron stars using the data from the Very Long Baseline Array (VLBA) and the Gaia space telescope operating, respectively, at radio and optical frequencies. The neutron stars studied in the thesis include the extremely magnetized magnetars, the fast-spinning millisecond pulsars, the gravitational-wave-emitting double neutron stars and neutron star X-ray binaries. As a major accomplishment, this thesis presents the novel analysis and the results of the MSPSRpi project — the largest astrometric survey of millisecond pulsars, then point out the abundant implications of the astrometric results. Additionally, the release of the astrometric results is bound to facilitate the detection of an ultra-low-frequency gravitational-wave background. Methodologically, this thesis applied advanced VLBI techniques to pulsar astrometry using the original data reduction pipeline psrvlbireduce, which leads to the first two significant magnetar parallaxes, and paves the way for studying magnetar formation channels with their velocity distribution. The astrometry Bayesian inference package sterne, developed during the PhD program, serves as a versatile and powerful tool for the inference of astrometric parameters.

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H. Ding
Tue, 20 Dec 22
36/97

Comments: PhD Thesis, 9 chapters, 241 pages, to be archived by the library of Swinburne University of Technology

Gravity, Horizons and Open EFTs [CL]

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http://arxiv.org/abs/2212.09157


Wilsonian effective theories exploit hierarchies of scale to simplify the description of low-energy behaviour and play as central a role for gravity as for the rest of physics. They are useful both when hierarchies of scale are explicit in a gravitating system and more generally for understanding precisely what controls the size of quantum corrections in gravitational systems. But effective descriptions are also relevant for open systems (e.g. fluid mechanics as a long-distance description of statistical systems) for which the `integrating out’ of unobserved low-energy degrees of freedom complicate a straightforward application of Wilsonian methods. Observations performed only on one side of an apparent horizon provide examples where open system descriptions also arise in gravitational physics. This chapter describes some early adaptations of Open Effective Theories (i.e. techniques for exploiting hierarchies of scale in open systems) in gravitational settings. Besides allowing the description of new types of phenomena (such as decoherence) these techniques also have an additional benefit: they sometimes can be used to resum perturbative expansions at late times and thereby to obtain controlled predictions in a regime where perturbative predictions otherwise generically fail.

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C. Burgess and G. Kaplanek
Tue, 20 Dec 22
50/97

Comments: 52 pages, 5 Figures; Invited chapter for the Section “Effective Quantum Gravity” edited by C. Burgess and J. Donoghue of the “Handbook of Quantum Gravity” (Eds. C. Bambi, L. Modesto and I.L. Shapiro, Springer Singapore, expected in 2023)

Prospects for constraining twin stars with next-generation gravitational-wave detectors [HEAP]

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http://arxiv.org/abs/2212.09733


Neutron star equations of state with strong phase transitions may support twin stars, hybrid and hadronic stars with the same mass but different tidal deformabilities. The presence of twin stars in the population of merging neutron stars produces distinctive gaps in the joint distribution of binary tidal deformabilities and chirp masses. We analyze a simulated population of binary neutron star mergers recovered with a network of next-generation (XG) ground-based gravitational-wave detectors to determine how many observations are needed to infer, or rule out, the existence of twin stars. Using a hierarchical inference framework based on a simple parametric twin-star model, we find that a single week of XG observations may suffice to detect a tidal deformability difference of several hundred between twins and measure the mass scale at which twins occur to within a few percent. For less pronounced twins, XG observations will place a stringent upper bound on the tidal deformability difference.

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P. Landry and K. Chakravarti
Tue, 20 Dec 22
56/97

Comments: 13 pages, 12 figures, 1 table

Quantum recoherence in the early universe [CL]

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http://arxiv.org/abs/2212.09486


Despite being created through a fundamentally quantum-mechanical process, cosmological structures have not yet revealed any sign of genuine quantum correlations. Among the obstructions to the direct detection of quantum signatures in cosmology, environmental-induced decoherence is arguably one of the most inevitable. Yet, we discover a mechanism of quantum recoherence for the adiabatic perturbations when they couple to an entropic sector. After a transient phase of decoherence, a turning point is reached, recoherence proceeds and adiabatic perturbations exhibit a large amount of self-coherence at late-time. This result is also understood by means of a non-Markovian master equation, which reduces to Wilsonian effective-field theory in the unitary limit. This allows us to critically assess the validity of open-quantum-system methods in cosmology and to highlight that re(de)coherence from linear interactions has no flat-space analogue.

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T. Colas, J. Grain and V. Vennin
Tue, 20 Dec 22
59/97

Comments: 5 + 12 pages, 4 + 2 figures

TASI Lectures on Cosmic Signals of Fundamental Physics [CL]

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http://arxiv.org/abs/2212.08685


The history of the Universe and the forces that shaped it are encoded in maps of the cosmos. From understanding these maps, we gain insights into nature that are inaccessible by other means. Unfortunately, the connection between fundamental physics and cosmic observables is often left to experts (and/or computers), making the general lessons from data obscure to many particle theorists. Fortunately, the same basic principles that govern the interactions of particles, like locality and causality, also control the evolution of the Universe as a whole and the manifestation of new physics in data. By focusing on these principles, we can understand more intuitively how the next generation of cosmic surveys will inform our understanding of fundamental physics. In these lectures, we will explore this relationship between theory and data through three examples: light relics ($N_{\rm eff}$) and the cosmic microwave background (CMB), neutrino mass and gravitational lensing of the CMB, and primordial non-Gaussianity and the distribution of galaxies. We will discuss both the theoretical underpinnings of these signals and the real-world obstacles to making the measurements.

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D. Green
Tue, 20 Dec 22
62/97

Comments: 72 pages, 14 figures, 2 tables

Black holes in asymptotically safe gravity and beyond [CL]

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http://arxiv.org/abs/2212.09495


Asymptotically safe quantum gravity is an approach to quantum gravity that achieves formulates a standard quantum field theory for the metric. Therefore, even the deep quantum gravity regime, that is expected to determine the true structure of the core of black holes, is described by a spacetime metric. The essence of asymptotic safety lies in a new symmetry of the theory — quantum scale symmetry — which characterizes the short-distance regime of quantum gravity. It implies the absence of physical scales. Therefore, the Newton coupling, which corresponds to a scale, namely the Planck length, must vanish asymptotically in the short-distance regime. This implies a weakening of the gravitational interaction, from which a resolution of classical spacetime singularities can be expected. In practise, properties of black holes in asymptotically safe quantum gravity cannot yet be derived from first principles, but are constructed using a heuristic procedure known as Renormalization Group improvement. The resulting asymptotic-safety inspired black holes have been constructed both for vanishing and for nonvanishing spin parameter. They are characterized by (i) the absence of curvature singularities, (ii) a more compact event horizon and photon sphere, (iii) a second (inner) horizon even at vanishing spin and (iv) a cold remnant as a possible final product of the Hawking evaporation. Observations can start to constrain the quantum-gravity scale that can be treated as a free parameter in asymptotic-safety inspired black holes. For slowly-spinning black holes, constraints from the EHT and X-ray observations can only constrain quantum-gravity scales far above the Planck length. In the limit of near-critical spin, asymptotic-safety inspired black holes may “light up” in a way the ngEHT may be sensitive to, even for a quantum-gravity scale equalling the Planck length.

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A. Eichhorn and A. Held
Tue, 20 Dec 22
71/97

Comments: invited chapter for the book ”Regular Black Holes: Towards a New Paradigm of the Gravitational Collapse”; comments welcome

Tests of general relativity in the nonlinear regime: a parametrized plunge-merger-ringdown gravitational waveform model [CL]

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http://arxiv.org/abs/2212.09655


The plunge-merger stage of the binary-black-hole (BBH) coalescence, when the bodies’ velocities reach a large fraction of the speed of light and the gravitational-wave (GW) luminosity peaks, provides a unique opportunity to probe gravity in the dynamical and nonlinear regime. How much do the predictions of general relativity differ from the ones in other theories of gravity for this stage of the binary evolution? To address this question, we develop a parametrized waveform model, within the effective-one-body formalism, that allows for deviations from general relativity in the plunge-merger-ringdown stage. As first step, we focus on nonprecessing-spin, quasicircular BBHs. In comparison to previous works, for each GW mode, our model can modify, with respect to general-relativistic predictions, the instant at which the amplitude peaks, the instantaneous frequency at this time instant, and the value of the peak amplitude. We use this waveform model to explore several questions considering both synthetic-data injections and two GW signals. In particular, we find that deviations from the peak GW amplitude and instantaneous frequency can be constrained to about 20$\%$ with GW150914. Alarmingly, we find that GW200129_065458 shows a strong violation of general relativity. We interpret this result as a false violation, either due to waveform systematics (mismodeling of spin precession) or due to data-quality issues depending on one’s interpretation of this event. This illustrates the use of parametrized waveform models as tools to investigate systematic errors in plain general relativity. The results with GW200129_065458 also vividly demonstrate the importance of waveform systematics and of glitch mitigation procedures when interpreting tests of general relativity with current GW observations.

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E. Maggio, H. Silva, A. Buonanno, et. al.
Tue, 20 Dec 22
74/97

Comments: 16+4 pages, 14 figures

The Hitchhiker's guide to the galaxy catalog approach for gravitational wave cosmology [CL]

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http://arxiv.org/abs/2212.08694


We outline the “dark siren” galaxy catalog method for cosmological inference using gravitational wave (GW) standard sirens, clarifying some common misconceptions in the implementation of this method. When a confident transient electromagnetic counterpart to a GW event is unavailable, the identification of a unique host galaxy is in general challenging. Instead, as originally proposed by Schutz (1986), one can consult a galaxy catalog and implement a dark siren statistical approach incorporating all potential host galaxies within the localization volume. Trott & Hunterer 2021 recently claimed that this approach results in a biased estimate of the Hubble constant, $H_0$, when implemented on mock data, even if optimistic assumptions are made. We demonstrate explicitly that, as previously shown by multiple independent groups, the dark siren statistical method leads to an unbiased posterior when the method is applied to the data correctly. We highlight common sources of error possible to make in the generation of mock data and implementation of the statistical framework, including the mismodeling of selection effects and inconsistent implementations of the Bayesian framework, which can lead to a spurious bias.

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J. Gair, A. Ghosh, R. Gray, et. al.
Tue, 20 Dec 22
85/97

Comments: 19 pages, 11 figures. Submitted to ApJ

A Dark Matter Trigger for Early Dark Energy Coincidence [CEA]

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http://arxiv.org/abs/2212.08098


Early dark energy (EDE), whose cosmological role is localized in time around the epoch of matter-radiation equality in order to resolve the Hubble tension, introduces a new coincidence problem: why should the EDE dynamics occur near equality if EDE is decoupled from both matter and radiation? The resolution of this problem may lie in an {\it early dark sector} (EDS), wherein the dark matter mass is dependent on the EDE scalar field. Concretely, we consider a Planck-suppressed coupling of EDE to dark matter, as would naturally arise from breaking of the global $U(1)$ shift symmetry of the former by quantum gravity effects. With a sufficiently flat potential, the rise to dominance of dark matter at matter-radiation equality itself triggers the rolling and subsequent decay of the EDE. We show that this {\it trigger} EDS (tEDS) model can naturally resolve the EDE coincidence problem at the background level without any fine tuning of the coupling to dark matter or of the initial conditions. When fitting to current cosmological data, including that from the local distance ladder and the low-redshift amplitude of fluctuations, the tEDS maximum-likelihood model performs comparably to EDE for resolving the Hubble tension, achieving $H_0 =71.2$ km/s/Mpc. However, fitting the \emph{Planck} cosmic microwave background data requires a specific range of initial field positions to balance the scalar field fluctuations that drive acoustic oscillations, providing testable differences with other EDE models.

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M. Lin, E. McDonough, J. Hill, et. al.
Mon, 19 Dec 22
7/62

Comments: 12 pages, 6 figures

Production of relic gravitational waves and the baryon asymmetry of the universe by random hypermagnetic fields [CL]

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http://arxiv.org/abs/2212.08483


We study the evolution of hypermagnetic fields (HMFs) in random plasma in the symmetric phase of the early universe. The system of kinetic equations for the spectra of the energy density and the helicity, as well as the particles asymmetries is derived. We also formulate the initial condition which involve the Kazantsev and Kolmogorov spectra of the seed HMFs. This system is solved numerically. We predict the energy spectrum of primeval gravitational waves which are produced by these HMFs. Additionally, the baryon asymmetry of the universe, generated by the lepton asymmetries, is obtained. These results allow us to constrain the strength of seed HMFs.

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M. Dvornikov
Mon, 19 Dec 22
8/62

Comments: 10 pages in LaTeX2e, 6 eps figures; contribution to proceedings of the 6th International Conference on Particle Physics and Astrophysics (November 29 – December 2, 2022, Moscow, Russia)

Effect of a High-Precision Semi-Analytical Mass Function on the Merger Rate of Primordial Black Holes in Dark Matter Halos [CEA]

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http://arxiv.org/abs/2212.08646


In this work, we study the effect of a high-precision semi-analytical mass function on the merger rate of primordial black holes (PBHs) in dark matter halos. For this purpose, we first explain a theoretical framework for dark matter halo models and introduce relevant quantities such as halo density profile, concentration parameter, and a high-precision semi-analytical function namely Del Popolo (DP) mass function. In the following, we calculate the merger rate of PBHs in the framework of ellipsoidal-collapse dark matter halo models while considering the DP mass function, and compare it with our previous study for the Sheth-Tormen (ST) mass function. The results show that by taking the mass of PBHs as $M_{PBH} = 30M_{\odot}$, the DP mass function predicts the amplification of the merger rate of PBHs to be in the range of $(42\pm 4)\%$. Moreover, we calculate the merger rate of PBHs for the DP mass function as a function of their mass and fraction and compare it with the black hole mergers recorded by the LIGO-Virgo detectors during the latest observing run. Our findings show that the merger rate of PBHs will fall within the LIGO-Virgo band if $f_{PBH} \gtrsim 0.1$. This implies that the DP mass function can be used to strengthen constraints on the fraction of PBHs. Moreover, our results demonstrate that for a mass range of $M_{PBH} = (10-100)M_{\odot}$, the relative amplification is predicted to be in the mean range of $(44.3 \pm 4.5)\%$.

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S. Fakhry and A. Popolo
Mon, 19 Dec 22
30/62

Comments: 9 pages, 4 figures, 1 table

Effective Field Theory for Large Scale Structure [CEA]

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http://arxiv.org/abs/2212.08488


This chapter is a non-expert introduction to the effective field theory of large scale structure. First, we give a detailed pedagogical explanation of why previous attempts to build non-linear cosmological perturbation theory failed. After that we introduce the description of dark matter as an effective non-ideal fluid and show how it corrects the shortcomings of the previous approaches. Finally, we develop a formulation of the effective field theory of large-scale structure from a nonequilibrium field theory perspective, called time-sliced perturbation theory. We show how this framework can be used for a consistent renormalization of cosmological correlation functions and a systematic resummation of large infrared effects relevant for the baryon acoustic oscillations.

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M. Ivanov
Mon, 19 Dec 22
35/62

Comments: 46 pages, 11 figures. Invited chapter for the Section “Effective Quantum Gravity” edited by C. Burgess and J. Donoghue of the “Handbook of Quantum Gravity” (Eds. C. Bambi, L. Modesto and I.L. Shapiro, Springer Nature, expected in 2023)

Power Spectra of Slow-Roll inflation in the consistent $D\to 4$ Einstein-Gauss-Bonnet gravity [CL]

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http://arxiv.org/abs/2212.08253


The slow-roll inflation which took place at extremely high energy regimes is in general believed to be sensitive to the high-order curvature corrections to the classical general relativity (GR). In this paper, we study the effects of the high-order curvature term, the Gauss-Bonnet (GB) term, on the primordial scalar and tensor spectra of the slow-roll inflation in the consistent $D \to 4$ Einstein Gauss-Bonnet (4EGB) gravity. The GB term is incorporated into gravitational dynamics via the re-scaling of the GB coupling constant $\alpha \to \alpha/(D-4)$ in the limit $ D\to 4$. For our purpose, we calculate explicitly the primordial scalar and tensor power spectra with GB corrections accurate to the next-to-leading order in the slow-roll approximation in the slow-roll inflation by using the third-order uniform asymptotic approximation method. The corresponding spectral indices and their runnings of the spectral indices for both the scalar and tensor perturbations as well as the ratio between the scalar and tensor spectra are also calculated up to the next-to-leading order in the slow-roll expansions. These results represent the most accurate results obtained so far in the literature.

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T. Li, T. Zhu and A. Wang
Mon, 19 Dec 22
36/62

Comments: 12 pages. arXiv admin note: text overlap with arXiv:1907.13108

Gravitational radiation from thermal mountains on accreting neutron stars: sources of temperature non-axisymmetry [HEAP]

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http://arxiv.org/abs/2212.07452


The spin-distribution of accreting neutron stars in low-mass X-ray binary (LMXB) systems shows a concentration of pulsars well below the Keplarian break-up limit. It has been suggested that their spin frequencies may be limited by the emission of gravitational waves, due to the presence of large-scale asymmetries in the internal temperature profile of the star. These temperature asymmetries have been demonstrated to lead to a non-axisymmetric mass-distribution, or `mountain’, that generates gravitational waves at twice the spin frequency. The presence of a toroidal magnetic field in the interior of accreting neutron stars has been shown to introduce such anisotropies in the star’s thermal conductivity, by restricting the flow of heat orthogonal to the magnetic field and establishing a non-axisymmetric temperature distribution within the star. We revisit this mechanism, extending the computational domain from (only) the crust to the entire star, incorporating more realistic microphysics, and exploring different choices of outer boundary condition. By allowing a magnetic field to permeate the core of the neutron star, we find that the likely level of temperature asymmetry in the inner crust ($\rho \sim 10^{13}$ g cm$^{-3}$) can be up to 3 orders of magnitude greater than the previous estimate, improving prospects for one day detecting continuous gravitational radiation. We also show that temperature asymmetries sufficiently large to be interesting for gravitational wave emission can be generated in strongly accreting neutron stars if crustal magnetic fields can reach $\sim 10^{12}$ G.

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T. Hutchins and D. Jones
Fri, 16 Dec 22
2/72

Comments: 26 pages, 21 figures

Unequal-mass boson-star binaries: Initial data and merger dynamics [CL]

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http://arxiv.org/abs/2212.08023


We present a generalization of the curative initial data construction derived for equal-mass compact binaries in Refs.[1,2] to arbitrary mass ratios. We demonstrate how these improved initial data avoid substantial spurious artifacts in the collision dynamics of unequal-mass boson-star binaries in the same way as has previously been achieved with the simpler method restricted to the equal-mass case. We employ the improved initial data to explore in detail the impact of phase offsets in the coalescence of equal- and unequal-mass boson star binaries.

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T. Evstafyeva, U. Sperhake, T. Helfer, et. al.
Fri, 16 Dec 22
7/72

Comments: 35 pages, 12 figures, submitted to CQG

Prospects for measuring dark energy with 21 cm intensity mapping experiments: A joint survey strategy [CEA]

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http://arxiv.org/abs/2212.07681


The 21 cm intensity mapping (IM) technique provides us with an efficient way to observe the cosmic large-scale structure (LSS). From the LSS data, one can use the baryon acoustic oscillation and redshift space distortion to trace the expansion and growth history of the universe, and thus measure the dark energy parameters. In this paper, we make a forecast for cosmological parameter estimation with the synergy of three 21 cm IM experiments. Specifically, we adopt a novel joint survey strategy, FAST ($0<z<0.35$)+SKA1-MID ($0.35<z<0.8$)+HIRAX ($0.8<z<2.5$), to measure dark energy. We simulate the 21 cm IM observations under the assumption of excellent foreground removal. We find that the synergy of three experiments could place quite tight constraints on cosmological parameters. For example, it provides $\sigma(\Omega_{\rm m})=0.0039$ and $\sigma(H_0)=0.27\ \rm km\ s^{-1}\ Mpc^{-1}$ in the $\Lambda$CDM model. Notably, the synergy could break the cosmological parameter degeneracies when constraining the dynamical dark energy models. Concretely, the joint observation offers $\sigma(w)=0.019$ in the $w$CDM model, and $\sigma(w_0)=0.085$ and $\sigma(w_a)=0.32$ in the $w_0w_a$CDM model. These results are better than or equal to those given by CMB+BAO+SN. In addition, when the foreground removal efficiency is relatively low, the strategy still performs well. Therefore, the 21 cm IM joint survey strategy is promising and worth pursuing.

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P. Wu, Y. Li, J. Zhang, et. al.
Fri, 16 Dec 22
9/72

Comments: 8 pages, 5 figures. arXiv admin note: text overlap with arXiv:2202.09726

The scaling of primordial gauge fields [CEA]

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http://arxiv.org/abs/2212.07929


It has been conjectured that a specific set of Cauchy data may lead to an unexpected growth of the gauge fields in conformally flat cosmological backgrounds. After introducing a class of models where the (hyper)magnetic fields are produced quantum mechanically from the early variation of the gauge coupling, we show that the standard evolution for wavelengths larger than the Hubble radius fully accounts for the anomalous scaling which is however unable to increase the magnetic power spectra. This dynamical evolution has nothing to do with a peculiar choice of the initial conditions but rather with the rate of variation of the gauge coupling during inflation. While the correct scaling follows from the properly normalized solutions of the mode functions and from the late dominance of the conductivity, a further amplification of the magnetic power spectra can only occur when the post-inflationary expansion rate is slower than radiation and it is again unrelated to the initial data possibly set during the inflationary stage.

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M. Giovannini
Fri, 16 Dec 22
11/72

Comments: 10 pages, 1 figure

Towards A Direct Detection of the Spin of Dark Matter [CL]

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http://arxiv.org/abs/2212.07442


We investigate the contribution of higher spin particles in the signal of direct detection experiments searching for dark matter. We consider a bosonic or fermionic higher spin dark matter (HSDM) candidate which interacts with the Standard Model via a dark U(1) mediator. For a particular subclass of interactions, spin-polarized targets may be used for spin determination: The angular dependence of scatterings can distinguish integer (spin-$s$) vs. half-integer (spin-$s + 1/2$), while the recoil energy dependence of the signal determines $s$. We consider also the signal of a supersymmetric higher spin dark sector, which suggests a characteristic signal (”SUSY Rilles”) for directional direct detection.

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L. Jenks, K. Koutrolikos, E. McDonough, et. al.
Fri, 16 Dec 22
15/72

Comments: 22 pages, 6 figures

Erasure of Strings and Vortexes [CL]

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http://arxiv.org/abs/2212.07535


The interaction of defects can lead to a phenomenon of erasure. During this process, a lower-dimensional object gets absorbed and dissolved by a higher-dimensional one. The phenomenon is very general and has a wide range of implications, both cosmological and fundamental. In particular, all types of strings, such as cosmic strings, QCD flux tubes, or fundamental strings, get erased when encountering a defect, either solitonic or a $D$-brane that deconfines their fluxes. This leads to a novel mechanism of cosmic string break-up, accompanied by gravitational and electromagnetic radiations. The arguments based on loss of coherence and the entropy count suggest that the erasure probability is very close to one, and strings never make it through the deconfining layer. We confirm this by a numerical simulation of the system, which effectively captures the essence of the phenomenon: a $2+1$-dimensional problem of interaction between a Nielsen-Olesen vortex of a $U(1)$ Higgs model and a domain wall inside which the $U(1)$ gauge group is unHiggsed and the magnetic flux is deconfined. In accordance with the entropy argument, in our simulation, the vortex never makes it across the wall.

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G. Dvali and J. Valbuena-Bermúdez
Fri, 16 Dec 22
20/72

Comments: 11 pages, 7 figures, the results of our numerical simulations can be visualized in the following \href{this https URL}{video}

Relaxing CMB bounds on Primordial Black Holes: the role of ionization fronts [CEA]

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http://arxiv.org/abs/2212.07969


The accretion of matter onto primordial black holes (PBHs) during the dark ages and the subsequent energy injection in the medium should have left imprints on the cosmic microwave background (CMB) anisotropies. Recent works have claimed stringent CMB limits on the PBH abundance, hardly compatible with a PBH interpretation of the gravitational-wave observations of binary BH mergers. By using a more realistic accretion model based on hydrodynamical simulations and conservative assumptions for the emission efficiency, we show that CMB limits on the PBH abundance are up to two orders of magnitude less stringent than previously estimated between $10$ and $10^4$ M$_\odot$. This reopens the possibility that PBHs might explain at the same time (at least a fraction of) the dark matter, some of the LIGO-Virgo-KAGRA binary BH mergers and the existence of super-massive BHs. More generally, we emphasize that PBH accretion can be a rather complex physical process with velocity dependences that are hard to assess, which introduces large uncertainties in accretion-based limits on the PBH abundance.

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G. Facchinetti, M. Lucca and S. Clesse
Fri, 16 Dec 22
26/72

Comments: 8 pages, 5 figures

A New Test of Dynamical Dark Energy Models and Cosmic Tensions in Hořava Gravity [CEA]

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http://arxiv.org/abs/2212.07683


Horava gravity has been proposed as a renormalizable, higher-derivative, Lorentz-violating quantum gravity model without ghost problems. A Horava gravity based dark energy (HDE) model for dynamical dark energy has been also proposed earlier by identifying all the extra (gravitational) contributions from the Lorentz-violating terms as an effective energy-momentum tensor in Einstein equation. We consider a complete CMB, BAO, and SNe Ia data test of the HDE model by considering general perturbations over the background perfect HDE fluid. Except from BAO, we obtain the preference of non-flat universes for all other data-set combinations. We obtain a positive result on the cosmic tensions between the Hubble constant H0 and the cosmic shear S8, because we have a shift of H0 towards a higher value, though not enough for resolving the H0 tension, but the value of S8 is unaltered. This is in contrast to a rather decreasing H0 but increasing S8 in a non-flat LCDM. For all other parameters, like Omega_m and Omega_Lambda, we obtain quite comparable results with those of LCDM for all data sets, especially with BAO, so that our results are close to a cosmic concordance between the datasets, contrary to the standard non-flat LCDM. We also obtain some undesirable features but we propose several promising ways for improvements by generalizing our analysis.

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E. Valentino, N. Nilsson and M. Park
Fri, 16 Dec 22
35/72

Comments: 21 pages, 10 figures

Measuring neutron-star distances and properties with gravitational-wave parallax [HEAP]

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http://arxiv.org/abs/2212.07506


Gravitational-wave astronomy allows us to study objects and events invisible to electromagnetic waves. So far, only signals triggered by coalescing binaries have been detected. However, as the interferometers’ sensitivities improve over time, we expect to observe weaker signals in the future, e.g. emission of continuous gravitational waves from spinning, isolated neutron stars. Parallax is a well-known method, widely used in electromagnetic astronomical observations, to estimate the distance to a source. In this work, we consider the application of the parallax method to gravitational-wave searches and explore possible distance estimation errors. We show that detection of parallax in the signal from a spinning down source can constrain the neutron star moment of inertia. For instance, we found that the relative error of the moment of inertia estimation is smaller than $10\%$ for all sources closer than 300 pc, for the assumed birth frequency of 700 Hz and for two years of observations by the Einstein Telescope.

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M. Sieniawska, D. Jones and A. Miller
Fri, 16 Dec 22
39/72

Comments: 6 pages, 7 figures, to be submitted to MNRAS

Isotropic Buchdahl's relativistic fluid sphere within $f(R,\,T)$ gravity [CL]

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http://arxiv.org/abs/2212.07810


The aim of the research is to look into a new solution for isotropic compact stars in the context of the $f(R,\,T)$ theory of gravity. We used the Buchdahl [H.A. Buchdahl, Phys. Rev. {\bf 116} (1959) 1027] metric potentials as input to deal with the field equations in the $f(R,\,T)$ framework. For different values of the coupling parameter $\chi$, graphical representation of the model parameters have been shown to canvass the analytical results more clearly. Interestingly, we have proven that for $\chi=0$, the standard General Relativity (GR) results can be recovered. A comparison of our obtained solutions with the GR results is also discussed. To study the effect of the coupling parameter $\chi$, the numerical values of the different physical variables have been tabulated for the values of the coupling parameter $\chi=0,\,0.25,\,0.5,\,0.75,1,\,1.25$. We used the compact stars candidate LMC X-4 with mass$=(1.04 \pm 0.09)M_{\odot}$; Radius $= 8.301_{-0.2}^{+0.2}$ km. respectively, for graphical analysis. To determine the physical acceptability of the model, we looked into the necessary physical properties such as energy conditions, causality, hydrostatic equilibrium, and pressure-density ratio etc. and found that our system satisfies all of these criteria, indicating that the model is physically reasonable.

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P. Bhar and P. Rej
Fri, 16 Dec 22
40/72

Comments: 15 Pages, 9 Figures ; Accepted for publication in New Astronomy on 14.12.2022 (Manuscript Number: NEWAST-D-22-00280R1). arXiv admin note: text overlap with arXiv:2112.07581

Dynamics and Equation of State Dependencies of Relevance for Nucleosynthesis in Supernovae and Neutron Star Mergers [HEAP]

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http://arxiv.org/abs/2212.07498


Neutron stars (NSs) and black holes (BHs) are born when the final collapse of the stellar core terminates the lives of stars more massive than about 9 Msun. This can trigger the powerful ejection of a large fraction of the star’s material in a core-collapse supernova (CCSN), whose extreme luminosity is energized by the decay of radioactive isotopes such as 56Ni and 56Co. When evolving in close binary systems, the compact relics of such infernal catastrophes spiral towards each other on orbits gradually decaying by gravitational-wave emission. Ultimately, the violent collision of the two components forms a more massive, rapidly spinning remnant, again accompanied by the ejection of considerable amounts of matter. These merger events can be observed by high-energy bursts of gamma rays with afterglows and electromagnetic transients called kilonovae, which radiate the energy released in radioactive decays of freshly assembled rapid neutron-capture elements. By means of their mass ejection and the nuclear and neutrino reactions taking place in the ejecta, both CCSNe and compact object mergers (COMs) are prominent sites of heavy-element nucleosynthesis and play a central role in the cosmic cycle of matter and the chemical enrichment history of galaxies. The nuclear equation of state (EoS) of NS matter, from neutron-rich to proton-dominated conditions and with temperatures ranging from about zero to ~100 MeV, is a crucial ingredient in these astrophysical phenomena. It determines their dynamical processes, their remnant properties even at the level of deciding between NS or BH, and the properties of the associated emission of neutrinos, whose interactions govern the thermodynamic conditions and the neutron-to-proton ratio for nucleosynthesis reactions in the innermost ejecta. This chapter discusses corresponding EoS dependent effects of relevance in CCSNe as well as COMs. (slightly abridged)

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H. Janka and A. Bauswein
Fri, 16 Dec 22
45/72

Comments: 96 pages, 23 figures; accepted for the Handbook of Nuclear Physics, eds. Isao Tanihata, Hiroshi Toki, Toshitaka Kajino

Spontaneous Scalarization of Black Holes in Gauss-Bonnet Teleparallel Gravity [CL]

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http://arxiv.org/abs/2212.07653


In this paper, we find new scalarized black holes by coupling a scalar field with the Gauss-Bonnet invariant in Teleparallel gravity. The Teleparallel formulation of this theory uses torsion instead of curvature to describe the gravitational interaction and it turns out that, in this language, the usual Gauss-Bonnet term in four dimensions, decays in two distinct boundary terms, the Teleparallel Gauss-Bonnet invariants. Both can be coupled individually, or in any combination, to a scalar field, to obtain a Teleparallel Gauss-Bonnet extension of the Teleparallel equivalent of general relativity. The theory we study contains the familiar Riemannian Einstein-Gauss-Bonnet gravity theory as a particular limit and offers a natural extension, in which scalarization is triggered by torsion and with new interesting phenomenology. We demonstrate numerically the existence of asymptotically flat scalarized black hole solutions and show that, depending on the choice of coupling of the boundary terms, they can have a distinct behaviour compared to the ones known from the usual Einstein-Gauss-Bonnet case. More specifically, non-monotonicity of the metric functions and the scalar field can be present, a feature that was not observed until now for static scalarized black hole solutions.

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S. Bahamonde, D. Doneva, L. Ducobu, et. al.
Fri, 16 Dec 22
50/72

Comments: 21 pages, 10 figures

Adiabatically compressed wave dark matter halo and intermediate-mass ratio inspirals [GA]

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http://arxiv.org/abs/2212.07528


The adiabatic growth of a central massive black hole could compress the surrounding dark matter halo, leading to a steeper profile of the dark matter halo. This phenomenon is called adiabatic compression. We investigate the adiabatic compression of wave dark matter – a light bosonic dark matter candidate with its mass smaller than a few eV. Using the adiabatic theorem, we show that the adiabatic compression leads to a much denser wave dark matter halo similar to the particle dark matter halo in the semiclassical limit. The compressed wave halo differs from that of the particle halo near the center where the semiclassical approximation breaks down, and the central profile depends on dark matter and the central black hole mass as they determine whether the soliton and low angular momentum modes can survive over the astrophysical time scale without being absorbed by the black hole. Such a compressed profile has several astrophysical implications. As one example, we study the gravitational waves from the inspiral between a central intermediate-mass black hole and a compact solar-mass object within the wave dark matter halo. Due to the enhanced mass density, the compressed wave dark matter halo exerts stronger dynamical friction on the orbiting object, leading to the dephasing of the gravitational waves. The pattern of dephasing is distinctive from that of inspirals in the particle dark matter halo because of the difference in density profile and because of the relatively suppressed dynamical friction force, originating from the wave nature of dark matter. We investigate the prospects of future gravitational wave detectors, such as Laser Interferometer Space Antenna, and identify physics scenarios where the wave dark matter halo can be reconstructed from gravitational wave observations.

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H. Kim, A. Lenoci, I. Stomberg, et. al.
Fri, 16 Dec 22
51/72

Comments: 17 pages, 8 figures

On highly compact Proca stars with quartic self-interactions [CL]

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http://arxiv.org/abs/2212.07659


We study self-gravitating bound states of a complex vector field, known as Proca stars, with a new type of quartic-order self-interaction which does not exist in the case of either a complex scalar field or a real vector field. Depending on the sign of the coupling constant, this quartic self-interaction can yield a distinct feature of Proca stars from the previously investigated self-interaction of the vector field. We find that self-gravitating solutions can be so compact that the photon sphere could form. However, we also show that the self-interaction gives rise to a ghost instability for the stars whose compactness is close that for the formation of a photon sphere, which might invalidate the formation of the photon sphere.

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K. Aoki and M. Minamitsuji
Fri, 16 Dec 22
53/72

Comments: 13 pages, 6 figures

Finite energy sum rules for gravitational Regge amplitudes [CL]

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http://arxiv.org/abs/2212.08001


We develop a framework to derive consistency constraints on gravitational Regge amplitudes based on the finite energy sum rules (FESRs), which directly connect gravitational Regge amplitudes at a finite ultraviolet scale with infrared physics without suffering from super-Planckian physics. For illustration, we consider four-point scattering of an identical massless scalar coupled to gravity. First, we derive multiple FESRs without relying on the $s\text{-}t\text{-}u$ permutation invariance. We then make use of FESRs, crossing symmetry, and other principles such as unitarity, to derive bounds on the Regge parameters. The bounds result in infrared finite gravitational positivity bounds in four spacetime dimensions.

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T. Noumi and J. Tokuda
Fri, 16 Dec 22
54/72

Comments: 22 pages plus appendices, 11 figures

Cosmic Web & Caustic Skeleton: non-linear Constrained Realizations – 2D case studies [CEA]

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http://arxiv.org/abs/2212.07840


The cosmic web consists of a complex configuration of voids, walls, filaments, and clusters, which formed under the gravitational collapse of Gaussian fluctuations. Understanding under what conditions these different structures emerge from simple initial conditions, and how different cosmological models influence their evolution, is central to the study of the large-scale structure. Here, we present a general formalism for setting up initial random density and velocity fields satisfying non-linear constraints for specialized N-body simulations. These allow us to link the non-linear conditions on the eigenvalue and eigenvector fields of the deformation tensor, as specified by caustic skeleton theory, to the current-day cosmic web. By extending constrained Gaussian random field theory, and the corresponding Hoffman-Ribak algorithm, to non-linear constraints, we probe the statistical properties of the progenitors of the walls, filaments, and clusters of the cosmic web. Applied to cosmological N-body simulations, the proposed techniques pave the way towards a systematic investigation of the evolution of the progenitors of the present-day walls, filaments, and clusters, and the embedded galaxies, putting flesh on the bones of the caustic skeleton. The developed nonlinear constrained random field theory is valid for generic cosmological conditions. For ease of visualization, the case study presented here probes the two-dimensional caustic skeleton.

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J. Feldbrugge and R. Weygaert
Fri, 16 Dec 22
57/72

Comments: 68 pages, 18 figures

Symmetric Teleparallel Horndeski [CL]

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http://arxiv.org/abs/2212.08005


Horndeski gravity is the most general scalar-tensor theory with one scalar field leading to second-order Euler-Lagrange field equations for the metric and scalar field, and it is based on Riemannian geometry. In this paper, we formulate an analogue version of Horndeski gravity in a symmetric teleparallel geometry which assumes that both the curvature (general) and torsion are vanishing and gravity is only related to nonmetricity. Our setup requires that the Euler-Lagrange equations for not only metric and scalar field but also connection should be at most second order. We find that the theory can be always recast as a sum of the Riemannian Horndeski theory and new terms that are purely teleparallel. Due to the nature of nonmetricity, there are many more possible ways of constructing second-order theories of gravity. In this regard, up to some assumptions, we find the most general $k$-essence extension of Symmetric Teleparallel Horndeski. We also formulate a novel theory containing higher-order derivatives acting on nonmetricity while still respecting the second-order conditions, which can be recast as an extension of Kinetic Gravity Braiding. We finish our study by presenting the FLRW cosmological equations for our model.

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S. Bahamonde, G. Trenkler, L. Trombetta, et. al.
Fri, 16 Dec 22
58/72

Comments: 34 pages

Searching for Domain Wall Network by Parkes Pulsar Timing Array [CL]

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http://arxiv.org/abs/2212.07871


We search for stochastic gravitational wave background generated by domain wall networks in the Data Release-2 of Parkes Pulsar Timing Array and find that the observed strong common power-law process can be explained by domain wall networks for the wall tension $\sigma_{\rm{DW}}\sim (29-414~\rm{TeV})^3$ and the wall-decay temperature $T_d\sim 26-363~\rm{MeV}$. Interestingly, the same parameter region can largely alleviate the Hubble tension, if the free particles generated from domain wall networks further decay into dark radiation. In addition, the preferred parameter space corresponds to the axion mass range $m_a \sim 10^{-13}-10^{-8}\ {\rm eV}$ for QCD axion. On the other hand, assuming that the common power-law process is not due to domain wall networks, we can put stringent constraints on the wall tension and decay temperature around the energy scale of QCD phase transition.

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L. Bian, S. Ge, C. Li, et. al.
Fri, 16 Dec 22
59/72

Comments: 18 pages, 13 figures, 4 tables. Comments welcome

Testing the Cosmological Principle with CatWISE Quasars: A Bayesian Analysis of the Number-Count Dipole [CEA]

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http://arxiv.org/abs/2212.07733


The Cosmological Principle, that the Universe is homogeneous and isotropic on sufficiently large scales, underpins the standard model of cosmology. However, a recent analysis of 1.36 million infrared-selected quasars has identified a significant tension in the amplitude of the number-count dipole compared to that derived from the CMB, thus challenging the Cosmological Principle. Here we present a Bayesian analysis of the same quasar sample, testing various hypotheses using the Bayesian evidence. We find unambiguous evidence for the presence of a dipole in the distribution of quasars with a direction that is consistent with the dipole identified in the CMB. However, the amplitude of the dipole is found to be 2.7 times larger than that expected from the conventional kinematic explanation of the CMB dipole, with a statistical significance of $5.7\sigma$. To compare these results with theoretical expectations, we sharpen the $\Lambda$CDM predictions for the probability distribution of the amplitude, taking into account a number of observational and theoretical systematics. In particular, we show that the presence of the galactic plane mask causes a considerable loss of dipole signal due to a leakage of power into higher multipoles, exacerbating the discrepancy in the amplitude. By contrast, we estimate using probabilistic arguments that the source evolution of quasars improves the discrepancy, but only mildly so. These results support the original findings of an anomalously large quasar dipole, independent of the statistical methodology used.

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L. Dam, G. Lewis and B. Brewer
Fri, 16 Dec 22
64/72

Comments: 9+5 pages, 6 figures

Might the 2PN perihelion precession of Mercury become measurable in the next future? [CL]

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http://arxiv.org/abs/2212.07323


The Hermean average perihelion rate $\dot\omega^\mathrm{2PN}$, calculated to the second post-Newtonian (2PN) order with the Gauss perturbing equations and the osculating Keplerian orbital elements, ranges from $-18$ to $-4$ microarcseconds per century $\left(\mu\mathrm{as\,cty}^{-1}\right)$, depending on the true anomaly at epoch $f_0$. It is the sum of four contributions: one of them is the direct consequence of the 2PN acceleration entering the equations of motion, while the other three are indirect effects of the 1PN component of the Sun’s gravitational field. An evaluation of the merely formal uncertainty of the experimental Mercury’s perihelion rate $\dot\omega_\mathrm{exp}$ recently published by the present author, based on 51 years of radiotechnical data processed with the EPM2017 planetary ephemerides by the astronomers E.V. Pitjeva and N.P. Pitjev, is $\sigma_{\dot\omega_\mathrm{exp}}\simeq 8\,\mu\mathrm{as\,cty}^{-1}$, corresponding to a relative accuracy of $2\times 10^{-7}$ for the combination $\left(2 + 2\gamma – \beta\right)/3$ of the PPN parameters $\beta$ and $\gamma$ scaling the well known 1PN perihelion precession. In fact, the realistic uncertainty may be up to $\simeq 10-50$ times larger, despite reprocessing the now available raw data of the former MESSENGER mission with a recent improved solar corona model should ameliorate our knowledge of the Hermean orbit. The BepiColombo spacecraft, currently en route to Mercury, might reach a $\simeq 10^{-7}$ accuracy level in constraining $\beta$ and $\gamma$ in an extended mission, despite $\simeq 10^{-6}$ seems more likely according to most of the simulations currently available in the literature. Thus, it might be that in the not too distant future it will be necessary to include the 2PN acceleration in the Solar System’s dynamics as well.

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L. Iorio
Thu, 15 Dec 22
1/75

Comments: LaTex2e, 11 pages, 1 figure, no tables

The graviton four-point function in de Sitter space [CL]

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http://arxiv.org/abs/2212.07370


We compute the tree-level late-time graviton four-point correlation function, and the related quartic wavefunction coefficient, for Einstein gravity in de Sitter spacetime. We derive this result in several ways: by direct calculation, using the in-in formalism and the wavefunction of the universe; by a heuristic derivation leveraging the flat space wavefunction coefficient; and by using the boostless cosmological bootstrap, in particular the combination of the cosmological optical theorem, the amplitude limit, and the manifestly local test. We find agreement among the different methods.

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J. Bonifacio, H. Goodhew, A. Joyce, et. al.
Thu, 15 Dec 22
3/75

Comments: 46 pages

Massive black hole assembly in nuclear star clusters [HEAP]

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http://arxiv.org/abs/2212.06845


Nuclear star clusters, that fragment into metal-poor stars in situ at the centers of protogalaxies, provide ideal environments for the formation of intermediate-mass black holes with masses $10^3-10^6M_\odot$. We utilize the semi-analytic model implemented in Rapster, a public rapid cluster evolution code. We implement simple recipes for stellar collisions and gas accretion/expulsion into the code and identify the regimes where each channel contributes to the dynamical formation of intermediate-mass black holes via repeated mergers of stellar black-hole seeds. We find that intermediate-mass black hole formation is almost inevitable if the initial mean density of the nuclear cluster is $>10^8M_\odot{\rm pc}^{-3}$. Million solar mass black holes can form within 100 Myr in the heaviest ($>10^7M_\odot$) and most compact ($<0.5~{\rm pc}$) nuclear clusters. We demonstrate that by today these resemble the observed range of nuclear clusters in dwarf galaxies and that there are potential gravitational-wave signatures of the massive black-hole formation process.

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K. Kritos, E. Berti and J. Silk
Thu, 15 Dec 22
9/75

Comments: 13 pages, 7 figures

Phantom attractors in Kinetic Gravity Braiding theories: A dynamical system approach [CL]

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http://arxiv.org/abs/2212.02547


We revise the expansion history of the scalar field theories known as kinetic gravity braiding models. These theories are well-known for the possibility of driving the expansion of the cosmos towards a future self-tuning de Sitter state when the corresponding Lagrangian is invariant under constant shifts in the scalar field. Nevertheless, this is not the only possible future fate of these shift-symmetric models. Using a dynamical system formulation we show that future cosmological singularities can also appear in this framework. Moreover, we present explicit examples where the future attractor in the configuration space of the theory corresponds to a big rip singularity.

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T. Vasilev, M. Bouhmadi-López and P. Martín-Moruno
Thu, 15 Dec 22
35/75

Comments: v1: 22 pages, 4 tables; v2: three references added, no physics changes

GALLIFRAY — A geometric modeling and parameter estimation framework for black hole images using bayesian techniques [IMA]

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http://arxiv.org/abs/2212.06827


Recent observations of the galactic centers of M87 and the Milky Way with the Event Horizon Telescope have ushered in a new era of black hole based tests of fundamental physics using very long baseline interferometry (VLBI). Being a nascent field, there are several different modeling and analysis approaches in vogue (e.g., geometric and physical models, visibility and closure amplitudes, agnostic and multimessenger priors). We present \texttt{GALLIFRAY}, an open-source Python-based framework for estimation/extraction of parameters using VLBI data. It is developed with modularity, efficiency, and adaptability as the primary objectives. This article outlines the design and usage of \texttt{GALLIFRAY}. As an illustration, we fit a geometric and a physical model to simulated datasets using markov chain monte carlo sampling and find good convergence of the posterior distribution. We conclude with an outline of further enhancements currently in development.

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S. Saurabh and S. Nampalliwar
Thu, 15 Dec 22
62/75

Comments: 10 pages, 5 figures. Comments are welcome!

Quantum Tunneling of Ultralight Dark Matter Out of Satellite Galaxies [CEA]

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http://arxiv.org/abs/2212.07386


The idea of ultralight scalar (axion) dark matter is theoretically appealing and may resolve some small-scale problems of cold dark matter; so it deserves careful attention. In this work we carefully analyze tunneling of the scalar field in dwarf satellites due to the tidal gravitational force from the host halo. The tidal force is far from spherically symmetric; causing tunneling along the axis from the halo center to the dwarf, while confining in the orthogonal plane. We decompose the wave function into a spherical term plus higher harmonics, integrate out angles, and then numerically solve a residual radial Schr\”odinger-Poisson system. By demanding that the core of the Fornax dwarf halo can survive for at least the age of the universe places a bound on the dark matter particle mass $2\times 10^{-22}\,\mbox{eV}\lesssim m\lesssim 6\times 10^{-22}\,$eV. Interestingly, we show that if another very low density halo is seen, then it rules out the ultralight scalar as core proposal completely. Furthermore, the non-condensed particles likely impose an even sharper lower bound. We also determine how the residual satellites could be distributed as a function of radius.

Read this paper on arXiv…

M. Hertzberg and A. Loeb
Thu, 15 Dec 22
68/75

Comments: 6 pages, 2 figures, in double column format