Tag Archives: General Relativity and Quantum Cosmology

Binary neutron star mergers in Einstein-scalar-Gauss-Bonnet gravity [CL]

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http://arxiv.org/abs/2208.09488


Binary neutron star mergers, which can lead to less massive black holes relative to other known astrophysical channels, have the potential to probe modifications to general relativity that arise at smaller curvature scales compared to more massive compact object binaries. As a representative example of this, here we study binary neutron star mergers in shift-symmetric Einstein-scalar-Gauss-Bonnet gravity using evolutions of the full, non-perturbative evolution equations. We find that the impact on the inspiral is small, even at large values of the modified gravity coupling (as expected, as neutron stars do not have scalar charge in this theory). However, post-merger there can be strong scalar effects, including radiation. When a black hole forms, it develops scalar charge, impacting the ringdown gravitational wave signal. In cases where a longer-lived remnant star persists post-merger, we find that the oscillations of the star source levels of scalar radiation similar to the black hole formation cases. In remnant stars, we further find that at coupling values comparable to the maximum value for which black hole solutions of the same mass exist, there is significant nonlinear enhancement in the scalar field, which if sufficiently large lead to a breakdown in the evolution, seemingly due to loss of hyperbolicity of the underlying equations.

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W. East and F. Pretorius
Tue, 23 Aug 22
57/79

Comments: 12 pages, 10 figures

Phenomenological signatures of gauge invariant theories of gravity with vectorial and gradient nonmetricity [CL]

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http://arxiv.org/abs/2208.10048


In this paper we discuss on the phenomenological footprints of theories where the gravitational effects are due not only to spacetime curvature, but also to nonmetricity. These theories are characterized by gauge invariance. Due to their simplicity, here we focus in theories with vectorial nonmetricity. We make special emphasis in gradient nonmetricity theories which are based in Weyl integrable geometry (WIG) spaces. While arbitrary and vectorial nonmetricities may have played a role in the quantum epoch, gradient nonmetricity can be important for the description of gravitational phenomena in our classical world instead. This would entail that gauge symmetry may be an actual symmetry of our past, present and future universe, without conflict with the standard model of particles (SMP). We show that, in a gauge invariant world modeled by WIG spacetime, the vacuum energy density is a dynamical quantity, so that the cosmological constant problem (CCP) may be avoided. Besides, due to gauge invariance, and to the fact that photons and radiation do not interact with nonmetricity, the accelerated pace of cosmic expansion can be explained without the need for the dark energy. We also discuss on the “many-worlds” interpretation of the resulting gauge invariant framework, where general relativity (GR) is just a specific gauge of the theory. The unavoidable discrepancy between the present value of the Hubble parameter computed on the GR basis and its value according to the gauge invariant theory, may explain the Hubble tension issue. It will be shown also that, due to gauge freedom, inflation is not required in order to explain the flatness, horizon and relict particles abundance problems within the present framework.

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I. Quiros
Tue, 23 Aug 22
62/79

Comments: 31 pages, 3 figures. Comments wellcome

Attempt to obtain the general relativistic planet's motion by special relativity techniques [EPA]

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http://arxiv.org/abs/2208.09297


It is attempted to derive the general relativistic (GR) equation of motion for planet and its solution solely by the special relativity (SR) techniques. The motion of a planet relative to the sun and that of the sun to the planet are solved independently in special relativistic framework using the perturbation theory in the celestial mechanics. The solution reveals a nature of the structure of the spacetime under the gravitation of the sun, and then its effect on the planet’s motion is examined. When the motion thus examined are compared with the one obtained by the general relativity theory in PN approximation, both are different concerning the mean motion and the radius of the orbit but exactly the same as for the perihelion precession.

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Y. Kubo
Mon, 22 Aug 22
25/53

Comments: 11 pages, 1 figure

Cylindrically symmetric radial accretion onto a Levi-Civita string-like source [CL]

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http://arxiv.org/abs/2208.09024


Radial steady-state accretion of polytropic matter is investigated under cylindrical symmetry in the Levi-Civita background metric. The model can be considered as a cylindrical analog of Bondi accretion in strong gravitational field. As a byproduct of this study, the issue of defining the line mass density is addressed and the role of the metric free parameters is discussed on the example of physical observables. The form of radial accretion equations is insensitive to the structure of the interior solution. Accordingly, the accretion solution analysis can be limited to a special Wilson form of Levi-Civita metric describing a structureless homogeneous string.

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&. Bratek, J. Jałocha and M. Kutschera
Mon, 22 Aug 22
26/53

Comments: This is not the final published version

Overcoming 1 part in $10^9$ of Earth angular rotation rate measurement with the G Wettzell data [CL]

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http://arxiv.org/abs/2208.09134


The absolute measurement of the Earth angular rotation rate with ground-based instruments becomes challenging if the 1 part in $10^9$ of precision has to be obtained. This threshold is important for fundamental physics and for geodesy, to investigate effects of General Relativity and Lorentz violation in the gravity sector and to provide the fast variation of the Earth rotation rate.
High sensitivity Ring Laser Gyroscopes (RLG) are currently the only promising technique to achieve this task in the near future, but their precision has been so far limited by systematics related to the laser operation.
In this paper we analyze two different sets of observations, each of them three days long. They were obtained from the G ring laser at the Geodetic Observatory Wettzell. The applied method has been developed for the GINGERINO ring laser in order to identify and extract the laser systematics. For the available data sets the residuals show mostly white noise behavior and the Allan deviation drops below 1 part in $10^9$ after an integration time of about $10^4$~s.

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A. Virgilio, G. Terreni, A. Basti, et. al.
Mon, 22 Aug 22
38/53

Comments: 10 pages, 6 figures

Regularization of Single Field Inflation Models [CEA]

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http://arxiv.org/abs/2208.09390


There are many single field inflationary models that are consistent with the recent Planck 2018 measurements of the spectral index $n_s$ and tensor-to-scalar ratio $r$. Despite good agreement with observational data some of these models suffer from having unregularized potentials which would produce a collapsing universe shortly after the end of inflation. In this paper we show that how one chooses to correct the behaviour potential towards the end of inflation can have a significant effect on the inflationary predictions of the model, specifically in the case of quartic hilltop and radiatively corrected Higgs inflation.

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J. Hoffmann and D. Sloan
Mon, 22 Aug 22
50/53

Comments: 24 pages, 25 figures

The inheritance of energy conditions: Revisiting no-go theorems in string compactifications [CL]

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http://arxiv.org/abs/2208.09341


One of the fundamental challenges in string theory is to derive realistic four-dimensional cosmological backgrounds from it and it has been recently shown that there are strict consistency conditions which must be satisfied in string compactifications, thus constraining its possible low-energy backgrounds. In this work, we focus on energy conditions as \textit{covariant and background independent} consistency requirements in order to classify possible backgrounds coming from low-energy string theory in two steps. Firstly, we show how supergravity actions typically obey many relevant energy conditions, under some reasonable assumptions. Remarkably, we find that the energy conditions are satisfied even in the presence of objects which individually violate them due to the tadpole cancellation condition. Thereafter, we list a set of required conditions for a higher-dimensional energy condition to imply the corresponding lower-dimensional one, thereby categorizing the allowed low-energy solutions. As for any no-go theorem, our aim is to highlight the assumptions which must be circumvented for deriving four-dimensional spacetimes that necessarily violate these energy conditions, with emphasis on cosmological backgrounds.

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H. Bernardo, S. Brahma and M. Faruk
Mon, 22 Aug 22
52/53

Comments: 20 pages

Repeating Fast Radio Bursts from Neutron Star Binaries: Multi-band and Multi-messenger Opportunities [HEAP]

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http://arxiv.org/abs/2208.08808


Recent observations indicate that magnetars commonly reside in merging compact binaries and at least part of fast radio bursts (FRBs) are sourced by magnetar activities. It is natural to speculate that a class of merging neutron star binaries may have FRB emitters. In this work, we study the observational aspects of these binaries – particularly those with FRB repeaters, which are promising multi-band and multi-messenger observation targets of radio telescopes and ground based gravitational wave detectors as the former telescopes can probe the systems at a much earlier stage in the inspiral than the latter. We show that observations of FRB repeaters in compact binaries have a significant advantage in pinning down the binary spin dynamics, constraining neutron star equation of state, probing FRB production mechanisms, and testing beyond standard physics. As a proof of principle, we investigate several mock observations of FRB pulses originating from pre-merger neutron star binaries, and we find that using the information of FRB arriving times alone, the intrinsic parameters of this system (including the stellar masses, spins, and quadrupole moments) can be measured with high precision, and the angular dependence of the FRB emission pattern can also be well reconstructed. The measurement of stellar masses (with an error of $\mathcal{O}(10^{-6}-10^{-5})$) and quadrupole moments (with an error of $\mathcal{O}(1\%-10\%)$) may be an unprecedented discriminator of nuclear equations of state in neutron stars. In addition, we find the multi-band and multi-messenger observations of this binary will be sensitive to alternative theories of gravity and beyond standard models, e.g., dynamical Chern-Simons gravity and axion field that is coupled to matter.

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Z. Pan, H. Yang and K. Yagi
Fri, 19 Aug 22
49/55

Comments: 17 pages, 12 figs, to be submitted

Black Hole Tidal Love Numbers and Dissipation Numbers in Worldline Effective Field Theory [CL]

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http://arxiv.org/abs/2208.08459


The worldine effective field theory (EFT) gives a gauge-invariant definition of black hole conservative tidal responses (Love numbers), dissipation numbers, and their spin-0 and spin-1 analogs. In the first part of this paper we show how the EFT allows us to circumvent the source/response ambiguity without having to use the analytic continuation prescription. The source/response ambiguity appears if Post-Newtonian (PN)corrections to external sources overlap with the response. However, these PN corrections can be clearly identified and isolated using the EFT.We illustrate that by computing static one-point functions of various external fields perturbing the four-dimensional Schwarzschild geometry. Upon resumming all relevant Feynman diagrams, we find that the PN terms that may mimic the response actually vanish for static black holes. Thus, the extraction of Love numbers from matching the EFT and general relativity (GR) calculations is completely unambiguous, and it implies that the Love numbers vanish identically for all types of perturbations. We also study in detail another type of fine tuning in the EFT, the absence of Love numbers’ running. We show that logarithmic corrections to Love numbers do stem from individual loop diagrams in generic gauges, but cancel after all diagrams are summed over.In the particular cases of spin-0 and spin-2 fields the logarithms are completely absent if one uses the Kaluza-Klein metric decomposition.In the second part of the paper we compute frequency-dependent dissipative response contributions to the one-point functions using the Schwinger-Keldysh formalism. We extract black hole dissipation numbers by comparing the one-point functions in the EFT and GR. Our results are in perfect agreement with those obtained from a manifestly gauge-invariant matching of absorption cross-sections.

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M. Ivanov and Z. Zhou
Fri, 19 Aug 22
50/55

Comments: 56 pages, comments are welcome

Sneutrinos as two inflatons and curvaton and leptogenesis [CL]

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http://arxiv.org/abs/2208.08296


We argue that sneutrinos can be embedded in a multi-field inflation framework where two inflatons and a curvaton simultaneously contribute to primordial fluctuations, which is consistent with current constraints on the spectral index and the tensor-to-scalar ratio from Planck and BICEP/Keck 2018. We also show that the same framework can also explain the baryon asymmetry of the Universe via leptogenesis realized by the decay of the lightest sneutrino. We investigate the parameter range for the scenario to work such as that of sneutrino masses. In particular, we show that the tensor-to-scalar ratio should be larger than $10^{-4}$ for a successful scenario.

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T. Takahashi, T. Yamada and S. Yokoyama
Thu, 18 Aug 22
4/45

Comments: 28 pages, 9 figures

Symmetry restoration in the vicinity of neutron stars with a nonminimal coupling [CL]

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http://arxiv.org/abs/2208.08107


We propose a new model of scalarized neutron stars (NSs) realized by a self-interacting scalar field $\phi$ nonminimally coupled to the Ricci scalar $R$ of the form $F(\phi)R$. The scalar field has a self-interacting potential and sits at its vacuum expectation value $\phi_v$ far away from the source. Inside the NS, the dominance of a positive nonminimal coupling over a negative mass squared of the potential leads to a symmetry restoration with the central field value $\phi_c$ close to $0$. This allows the existence of scalarized NS solutions connecting $\phi_v$ with $\phi_c$ whose difference is significant, whereas the field is located in the vicinity of $\phi=\phi_v$ for weak gravitational stars. The Arnowitt-Deser-Misner mass and radius of NSs as well as the gravitational force around the NS surface can receive sizable corrections from the scalar hair, while satisfying local gravity constraints in the Solar system. Unlike the original scenario of spontaneous scalarization induced by a negative nonminimal coupling, the catastrophic instability of cosmological solutions can be avoided. We also study the cosmological dynamics from the inflationary epoch to today and show that the scalar field $\phi$ finally approaches the asymptotic value $\phi_v$ without spoiling a successful cosmological evolution. After $\phi$ starts to oscillate about the potential minimum, the same field can also be the source for cold dark matter.

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M. Minamitsuji and S. Tsujikawa
Thu, 18 Aug 22
9/45

Comments: 19 pages, 5 figures

Dissimilar Donuts in the Sky? Effects of a Pressure Singularity on the Circular Photon Orbits and Shadow of a Cosmological Black Hole [CL]

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http://arxiv.org/abs/2208.07972


The black hole observations obtained so far indicate one thing: similar “donuts” exist in the sky. But what if some of the observed black hole shadows that will obtained in the future are different from the others? In this work the aim is to show that a difference in the shadow of some observed black holes in the future, might explain the $H_0$-tension problem. In this letter we investigate the possible effects of a pressure cosmological singularity on the circular photon orbits and the shadow of galactic supermassive black holes at cosmological redshifts. Since the pressure singularity is a global event in the Universe, the effects of the pressure singularity will be imposed on supermassive black holes at a specific redshift. As we show, the pressure singularity affects the circular photon orbits around cosmological black holes described by the McVittie metric, and specifically, for some time before the time instance that the singularity occurs, the photon orbits do not exist. We discuss the possible effects of the absence of circular photon orbits on the shadow of these black holes. Our idea indicates that if a pressure singularity occurred in the near past, then this could have a direct imprint on the shadow of supermassive galactic black holes at the redshift corresponding to the time instance that the singularity occurred in the past. Thus, if a sample of shadows is observed in the future for redshifts $z\leq 0.01$, and for a specific redshift differences are found in the shadows, this could be an indication that a pressure singularity occurred, and this global event might resolve the $H_0$-tension as discussed in previous work. However, the observation of several shadows at redshifts $z\leq 0.01$ is rather a far future task.

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S. Odintsov and V. Oikonomou
Thu, 18 Aug 22
13/45

Comments: EPL Accepted

Can primordial parity violation explain the observed cosmic birefringence? [CEA]

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http://arxiv.org/abs/2208.08101


Recently, the cross-correlation between $E$- and $B$-mode polarization of the cosmic microwave background (CMB), which is well explained by cosmic birefringence with rotation angle $\beta\approx 0.3$ deg, has been found in CMB polarization data. We carefully investigate the possibility of explaining the observed $EB$ correlation by the primordial chiral gravitational waves (CGWs), which can be generated in the parity-violating theories in the primordial Universe. We found that the CGWs scenario does not work due to the overproduction of the $BB$ auto-correlation which far exceeds the observed one by SPTPol and POLARBEAR.

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T. Fujita, Y. Minami, M. Shiraishi, et. al.
Thu, 18 Aug 22
21/45

Comments: 5 pages, 2 figures

Inflation with Stochastic Boundary [CL]

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http://arxiv.org/abs/2208.08229


We study the Brownian motion of a field where there are boundaries in the inflationary field space. Both the field and the boundary undergo Brownian motions with the amplitudes of the noises determined by the Hubble expansion rate of the corresponding dS spacetime. This setup mimics models of inflation in which curvature perturbation is induced from inhomogeneities generated at the surface of end of inflation. The cases of the drift dominated regime as well as the diffusion dominated regime are studied in details. We calculate the first hitting probabilities as well as the mean number of e-folds for the field to hit either of the boundaries in the field space. The implications for models of inflation are reviewed.

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A. Nassiri-Rad, K. Asadi and H. Firouzjahi
Thu, 18 Aug 22
30/45

Comments: N/A

Reheating era in Gauss-Bonnet theories of gravity compatible with the GW170817 event [CL]

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http://arxiv.org/abs/2208.08333


In the present article we showcase how the reheating era can be described properly in the context of Einstein-Gauss-Bonnet gravity assuming that the primordial gravitational waves propagate with the velocity of light. The equations of the duration of reheating along with the reheating temperature are derived and as demonstrated, their expressions are quite similar to the case of a canonical scalar field where now the second derivative of the Gauss-Bonnet scalar coupling function appears and effectively alters the numerical value of the scalar potential. The appearance of such term is reminiscing of a $\lambda R$ model of gravity where $\lambda$ is now dynamical. We consider two viable inflationary models of interest, the former involves an error function as scalar Gauss-Bonnet coupling function and the latter a Woods-Saxon scalar potential. It is shown that for both models the aforementioned quantities can be in agreement with theoretical expectations. The only constraint that is needed is the assumption that the second time derivative of the Gauss-Bonnet scalar coupling function is actually lesser than the Planck mass squared, that is $\ddot\xi<\frac{M_{Pl}^2}{8}$ in order to obtain a viable description. We find that a free parameter of the theory and specifically the potential amplitude for the Woods-Saxon model during the inflationary era, dictates the effective equations of state and therefore the reheating epoch can be described either by a type of stiff matter with EoS parameter equal to unity or by an EoS parameter close to that of the radiation.

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S. Venikoudis and F. Fronimos
Thu, 18 Aug 22
42/45

Comments: NPB Accepted

Parameter Estimation of Gravitational Waves with a Quantum Metropolis Algorithm [CL]

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http://arxiv.org/abs/2208.05506


After the first detection of a gravitational wave in 2015, the number of successes achieved by this innovative way of looking through the universe has not stopped growing. However, the current techniques for analyzing this type of events present a serious bottleneck due to the high computational power they require. In this article we explore how recent techniques based on quantum algorithms could surpass this obstacle. For this purpose, we propose a quantization of the classical algorithms used in the literature for the inference of gravitational wave parameters based on the well-known Quantum Walks technique applied to a Metropolis-Hastings algorithm. Finally, we compare this algorithm with its classical counterpart for all the events of the first GW catalog GWTC-1 for the estimation of different sets of parameters with increasing complexities and we find a polynomial advantage in the quantum algorithms, thus setting a first starting point for future algorithms.

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G. Escrig, R. Campos, P. Casares, et. al.
Thu, 18 Aug 22
44/45

Comments: RevTex 4.2, 3 color Figures and 1 Table

A note on the (non-)conservation of curvature perturbation [CL]

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http://arxiv.org/abs/2208.07568


In this note, we compare two different definitions for the cosmological perturbation $\zeta$ which is conserved on large scales and study their non-conservation on small scales. We derive an equation for the time evolution of the curvature perturbation on a uniform density slice through a calculation solely in longitudinal (conformal-Newtonian) gauge. The result is concise and compatible with that obtained via local conservation of energy-momentum tensor.

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C. Lin
Wed, 17 Aug 22
5/58

Comments: 8 pages

Nonlinear effects in black hole ringdown [CL]

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http://arxiv.org/abs/2208.07374


We report evidence for nonlinear modes in the ringdown stage of the gravitational waveform produced by the merger of two comparable-mass black holes. We consider both the coalescence of black hole binaries in quasicircular orbits and high-energy, head-on black hole collisions. The presence of nonlinear modes in the numerical simulations confirms that general-relativistic nonlinearities are important and must be considered in gravitational-wave data analysis.

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M. Cheung, V. Baibhav, E. Berti, et. al.
Wed, 17 Aug 22
29/58

Comments: 11 pages, 6 figures

Multiparameter tests of general relativity using principal component analysis with next-generation gravitational wave detectors [CL]

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http://arxiv.org/abs/2208.07757


Principal Component Analysis (PCA) is an efficient tool to optimize the multiparameter tests of general relativity (GR) where one tests for simultaneous deviations in multiple post-Newtonian (PN) phasing coefficients by introducing fractional deformation parameters. We use PCA to construct the `best-measured’ linear combinations of the PN deformation parameters from the data. This helps to set stringent limits on deviations from GR and detect possible beyond-GR physics. In this paper, we study the effectiveness of this method with the proposed next-generation gravitational wave detectors, Cosmic Explorer (CE) and Einstein Telescope (ET). Observation of compact binaries with total masses between 20-200 $\mathrm{M}_{\odot}$ in the detector frame and at a luminosity distance of 500 Mpc, CE can measure the three most dominant linear combinations to an accuracy better than 10%, and the most dominant one to better than 0.1%. For specific ranges of masses and linear combinations, constraints from ET are better by a few factors than CE. This improvement is because of the improved low frequency sensitivity of ET compared to CE (between 1-5 Hz). In addition, we explain the sensitivity of the PCA parameters to the different PN deformation parameters and discuss their variation with total mass. We also discuss a criterion for quantifying the number of most dominant linear combinations that capture the information in the signal up to a threshold.

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S. Datta, M. Saleem, K. Arun, et. al.
Wed, 17 Aug 22
34/58

Comments: N/A

Gravitational Waves with Dark Energy [CL]

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http://arxiv.org/abs/2208.06844


In this article, we study the tensor mode equation of perturbation in the presence of nonzero-Lambda as dark energy, the dynamic nature of which depends on the Hubble parameter H and/or its time derivative. Dark energy, according to the total vacuum contribution, has a slight effect during the radiation-dominated era, but it reduces the squared amplitude of gravitational waves (GWs) up to 60% for the wavelengths that enter the horizon during the matter-dominated era.

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J. Khodagholizadeh
Wed, 17 Aug 22
46/58

Comments: 19 pages, 3 Figure

Generation and propagation of nonlinear quasi-normal modes of a Schwarzschild black hole [CL]

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http://arxiv.org/abs/2208.07379


In the analysis of a binary black hole coalescence, it is necessary to include gravitational self-interactions in order to describe the transition of the gravitational wave signal from the merger to the ringdown stage. In this paper we study the phenomenology of the generation and propagation of nonlinearities in the ringdown of a Schwarzschild black hole, using second-order perturbation theory. Following earlier work, we show that the Green’s function and its causal structure determines how both first-order and second-order perturbations are generated, and hence highlight that both of these solutions inherit analogous properties. In particular, we discuss the sense in which both linear and quadratic quasi-normal modes (QNMs) are generated in the vicinity of the peak of the gravitational potential barrier (loosely referred to as the light ring). Among the second-order perturbations, there are solutions with linear QNM frequencies (whose amplitudes are thus renormalized from their linear values), as well as quadratic QNM frequencies with a distinct spectrum. Moreover, we show using a WKB analysis that, in the eikonal limit, waves generated inside the light ring propagate towards the black hole horizon, and only waves generated outside propagate towards an asymptotic observer. These results might be relevant for recent discussions on the validity of perturbation theory close to the merger. Finally, we argue that even if nonlinearities are small, quadratic QNMs may be detectable and would likely be useful for improving ringdown models of higher angular harmonics and future tests of gravity.

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M. Lagos and L. Hui
Wed, 17 Aug 22
56/58

Comments: N/A

Nonlinearities in black hole ringdowns [CL]

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http://arxiv.org/abs/2208.07380


The gravitational wave strain emitted by a perturbed black hole (BH) ringing down is typically modeled analytically using first-order BH perturbation theory. In this Letter we show that second-order effects are necessary for modeling ringdowns from BH merger simulations. Focusing on the strain’s $(\ell,m)=(4,4)$ angular harmonic, we show the presence of a quadratic effect across a range of binary BH mass ratios that agrees with theoretical expectations. We find that the quadratic $(4,4)$ mode amplitude exhibits quadratic scaling with the fundamental $(2,2)$ mode — its parent mode. The nonlinear mode’s amplitude is comparable to or even larger than that of the linear $(4,4)$ modes. Therefore correctly modeling ringdown — improving mismatches by an order of magnitude — requires the inclusion of nonlinear effects.

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K. Mitman, M. Lagos, L. Stein, et. al.
Wed, 17 Aug 22
57/58

Comments: 5+2 pages, 4 figures, 1 table

Measuring the Hubble Constant with Double Gravitational Wave Sources in Pulsar Timing [CEA]

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http://arxiv.org/abs/2208.06495


Pulsar timing arrays (PTAs) are searching for gravitational waves from supermassive black hole binaries (SMBHBs). Here we show how future PTAs could use a detection of gravitational waves from individually resolved SMBHB sources to produce a purely gravitational wave-based measurement of the Hubble constant. This is achieved by measuring two separate distances to the same source from the gravitational wave signal in the timing residual: the luminosity distance $D_L$ through frequency evolution effects, and the parallax distance $D_\mathrm{par}$ through wavefront curvature (Fresnel) effects. We present a generalized timing residual model including these effects in an expanding universe. Of these two distances, $D_\mathrm{par}$ is challenging to measure due to the pulsar distance wrapping problem, a degeneracy in the Earth-pulsar distance and gravitational wave source parameters that requires highly precise, sub-parsec level, pulsar distance measurements to overcome. However, in this paper we demonstrate that combining the knowledge of two SMBHB sources in the timing residual largely removes the wrapping cycle degeneracy. Two sources simultaneously calibrate the PTA by identifying the distances to the pulsars, which is useful in its own right, and allow recovery of the source luminosity and parallax distances which results in a measurement of the Hubble constant. We find that, with optimistic PTAs in the era of the Square Kilometer Array, two SMBHB sources within a few hundred Mpc could be used to measure the Hubble constant with a relative uncertainty on the order of 10 per cent.

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C. McGrath, D. D’Orazio and J. Creighton
Tue, 16 Aug 22
7/74

Comments: 23 pages, 11 figures. Submitted to the Monthly Notices of the Royal Astronomical Society. arXiv admin note: text overlap with arXiv:2109.07603

Testing the Hubble law with Pantheon+ [CEA]

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http://arxiv.org/abs/2208.07271


The Hubble law (HL) governs the low-redshift (low-z) evolution of the distance of an object. However, there is a lack of an investigation of its validity and effective radius for a long time, since the low-z background data with a high precision is scarce. The latest Type Ia supernovae sample Pantheon+ having a significant increase of low-z data provides an excellent opportunity to test the HL. We propose a generalized HL and implement the first modern test of the HL with Pantheon+. We obtain the constraint on the deviation parameter $\alpha=1.00118\pm0.00044$, confirm the validity of linear HL with a $0.04\%$ precision and give the transition redshift $z_t=0.03$ and luminosity distance $D_{L,t}=123.13\pm1.75$ Mpc, which means that HL holds when $z<0.03$ and breaks down at a distance of $D_L>123.13$ Mpc. Comparing the ability of Type Ia supernovae and HII galaxies in testing the HL, we stress the uniqueness and strong power of Type Ia supernovae in probing the low-z physics.

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D. Wang
Tue, 16 Aug 22
12/74

Comments: 4.5 pages, 5 figures. A modern test of Hubble law using Pantheon+

Domain wall networks from first-order phase transitions and gravitational waves [CL]

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http://arxiv.org/abs/2208.07186


In the first-order phase transitions (PTs) colliding bubble is an important gravitational wave (GW) source. Following bubble collision, domain walls can be formed when degenerate vacua occur as a result of the breaking of a discrete symmetry relevant to new physics at electroweak or higher scales. Using lattice simulations, we study the dynamical evolution of domain walls and find that the networks of the domain wall are formed around the completion of PTs and the lifetime of the wall networks largely depends on whether or not the degeneracy of true vacua is broken. Our numerical results indicate that domain wall networks continue to produce GWs in the aftermath of PTs, leading to dramatically changing the spectral shape and enhancing the magnitude by about one order. The resulting GW power spectra are peaked at $kR_* \simeq \pi$, above the peak wavenumber it has a decaying power law close to $k^{-1.2}$ followed by a slowly decreasing plateau with the UV cutoff at $kR_* \sim \mathcal{O}(10^2)$

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D. Wei and Y. Jiang
Tue, 16 Aug 22
18/74

Comments: 7 pages, 7 figures

Dark Energy Star in Gravity's Rainbow [CL]

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http://arxiv.org/abs/2208.07063


The concept of dark energy can be a candidate for preventing the gravitational collapse of compact objects to singularities. According to the usefulness of gravity’s rainbow in UV completion of general relativity (by providing a new description of spacetime), it can be an excellent option to study the behavior of compact objects near phase transition regions. In this work, we obtain a modified Tolman-Openheimer-Volkof (TOV) equation for anisotropic dark energy as a fluid by solving the field equations in gravity’s rainbow. Next, to compare the results with general relativity, we use a generalized Tolman-Matese-Whitman mass function to determine the physical quantities such as energy density, radial pressure, transverse pressure, gravity profile, and anisotropy factor of the dark energy star. We evaluate the junction condition and investigate the dynamical stability of dark energy star thin shell in gravity’s rainbow. We also study the energy conditions for the interior region of this star. We show that the coefficients of gravity’s rainbow can significantly affect this non-singular compact object and modify the model near the phase transition region.

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A. Tudeshki, G. Bordbar and B. Panah
Tue, 16 Aug 22
19/74

Comments: 13 pages, 8 figures

Shadows around at Sgr A* and M87* as a tool to test gravity theories [GA]

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http://arxiv.org/abs/2208.06805


In the framework of Randall — Sundrum theory with extra dimension Reissner — Nordstrom black hole solutions with a tidal charge have been found. The shadow around the supermassive black hole in M87 was reconstructed in 2019 based on observations with the Event Horizon Telescope (EHT) in April 2017. In May 2022 the EHT Collaboration presented results of a shadow reconstruction for our Galactic Center. Earlier, for Reissner — Nordstr\”om metric we derived analytical expressions for shadow size as a function of charge and later generalized these results for a tidal charge case. We discuss opportunities to evaluate parameters of alternative theories of gravity with shadow size estimates done by the EHT Collaboration, in particular, a tidal charge could be estimated from these observations.

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A. Zakharov
Tue, 16 Aug 22
25/74

Comments: 10 pages, 1 figure, presented at the ICRANet-ISFAHAN Astronomy Meeting

Models of modified-inertia formulation of MOND [GA]

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http://arxiv.org/abs/2208.07073


Models of modified-inertia' formulation of MOND are described and applied to nonrelativistic many-body systems. They involve time-nonlocal equations of motion. Momentum, angular momentum, and energy are (nonlocally) defined, whose total values are conserved for isolated systems. The models make all the salient MOND predictions. Yet, they differ from existingmodified-gravity’ formulations in some second-tier predictions. The models describe correctly the motion of a composite body in a low-acceleration field even when the internal accelerations of its constituents are high. They exhibit a MOND external field effect (EFE) that shows some important differences from what we have come to expect from modified-gravity versions: In one, simple example of the models, what determines the EFE, in the case of a dominant external field, is $\mu(\theta\langle a_{ex}\rangle/a_0)$, where $\mu(x)$ is the MOND interpolating function' that describes rotation curves, compared with $\mu(a_{ex}/a_0)$ for presently-knownmodified-gravity’ formulations. The two main differences are that while $a_{ex}$ is the momentary value of the external acceleration, $\langle a_{ex}\rangle$ is a certain time average of it, and that $\theta>1$ is an extra factor that depends on the frequency ratio of the external- and internal-field variations. Only ratios of frequencies enter, and $a_0$ remains the only new dimensioned constant. For a system on a circular orbit in a galaxy (such as the vertical dynamics in a disc galaxy), the first difference disappears, since $\langle a_{ex}\rangle=a_{ex}$. But the $\theta$ factor can appreciably enhance the EFE in quenching MOND effects, over what is deduced in modified gravity. Some exact solutions are also described, such as for rotation curves, for an harmonic force, and the general, two-body problem, which in the deep-MOND regime reduces to a single-body problem.

Read this paper on arXiv…

M. Milgrom
Tue, 16 Aug 22
33/74

Comments: 12 pages

Dynamical synchronization and the horizon problem [CL]

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http://arxiv.org/abs/2208.07104


The cosmological horizon problem is the question why spatial domains that were never in causal contact with each other now appear in precise symphony. We propose a solution to the horizon problem in which a globally synchronized early state is reached as the $\omega$-limit point of a transient, inhomogeneous Mixmaster universe. We show that the $\alpha$-limit set of the latter is a Kasner circle which represents a synchronized initial state of minimal entropy. Accordingly, unless the evolution is disrupted by quantum gravitational effects so that the initial state is not attained, Planck size domains emerge as causally disconnected, albeit in complete synchrony, as the universe enters an `isotropic’ state to remain so in future unison.

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S. Cotsakis
Tue, 16 Aug 22
42/74

Comments: 10 pages, 1 figure

An outlook on the estimate of the solar quadrupole moment from relativistic gravitation contributions [SSA]

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http://arxiv.org/abs/2208.06779


Of all the solar fundamental parameters (mass, diameter, gravity at the surface,…), the gravitational moments have been quite often ignored in the past, mainly due to the great difficulty to get a reliable estimate. Even though the order of magnitude of the solar quadrupole moment $J_2$ is now known to be $10^{-7}$, its accurate value is still discussed. Indeed, the expansion in multipoles $J_{(l,~ l = 2, …)}$ of the gravitational potential of a rotating body affects the orbital motion of planets at a relativistic level. We will recall here the recent progresses made in testing General Relativity through the contribution of the first solar quadrupole moment. Using the Eddington-Robertson parameters, we recall the constraints both on a theoretical and experimental point of view. Together with $\gamma$, which encodes the amount of curvature of space-time per unit rest-mass, the Post–Newtonian Parameter $\beta$ contributes to the relativistic precession of planets. The latter parameter encodes the amount of non-linearity in the superposition law of gravitation. Even though in principle, it would be possible to extract $J_2$ from planetary ephemerides, we observe that it is significantly correlated with other solution parameters (semi-major axis of planets, mass of asteroids…). Focusing on the $J_2$ correlations, we show that in general, when ~$\beta$ and ~$\gamma$ are freed, the correlations ~[$\beta, J_2$] and ~[$\gamma, J_2$] are $\approx$ 45\% and $\approx$ 55\% respectively. Moreover, all the planetary dynamics-based values are biased by the Lense–Thiring effect, which has never been modeled and solved for so far, but can be estimated to $\approx$ 7\%. It is thus possible to get a good estimate of the solar quadrupole moment:$1.66\times10^{-7}$$\leq$$J_2$$\leq$$2.32\times10^{-7}$.

Read this paper on arXiv…

J. Rozelot, A. Kilcik and Z. Fazel
Tue, 16 Aug 22
64/74

Comments: N/A

The Hellings and Downs correlation of an arbitrary set of pulsars [CL]

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http://arxiv.org/abs/2208.07230


Pulsar timing arrays (PTAs) detect gravitational waves (GWs) via the correlations that the waves induce in the arrival times of pulses from different pulsars. The mean correlation $\mu_{\rm u}(\gamma)$ as a function of the angle $\gamma$ between the directions to two pulsars was calculated by Hellings and Downs in 1983. The variance $\sigma^2_{\rm tot}(\gamma)$ in this correlation was recently calculated for a single pulsar pair at angle $\gamma$. Averaging over many such pairs, uniformly distributed on the sky, reduces this to an intrinsic cosmic variance $\sigma^2_{\rm cos}(\gamma)$. We extend that analysis to an arbitrary finite set of pulsars, distributed at specific sky locations, for which the pulsar pairs are grouped into finite-width bins in $\gamma$. Given (measurements or calculations of) the correlations for any set of pulsars, we find the best way to estimate the mean in each bin. The optimal estimator of the correlation takes into account correlations among all of the pulsars that contribute to that angular bin. We also compute the variance in the binned estimate. For narrow bins, as the number of pulsar pairs grows, the variance drops to the cosmic variance. For wider bins, by sacrificing angular resolution in $\gamma$, the variance can even be reduced below the cosmic variance. Our calculations assume that the GW signals are described by a Gaussian ensemble, which provides a good description of the confusion noise produced by expected PTA sources. We illustrate our methods with plots of the GW variance for the sets of pulsars currently monitored by several PTA collaborations. The methods can also be applied to future PTAs, where the improved telescopes will provide larger pulsar populations and higher-precision timing.

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B. Allen and J. Romano
Tue, 16 Aug 22
68/74

Comments: 28 pages, 9 figures, 1 table

One-parameter dynamical dark-energy from the generalized Chaplygin gas [CEA]

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http://arxiv.org/abs/2208.06302


The fact that Einstein’s equations connect the space-time geometry to the total matter content of the cosmic substratum, but not to individual contributions of the matter species, can be translated into a degeneracy in the cosmological dark sector. Such degeneracy makes it impossible to distinguish cases where dark energy (DE) interacts with dark matter (DM) from a dynamical non-interacting scenario using observational data based only on time or distance measurements. In this paper, based on the non-adiabatic generalized Chaplygin gas (gCg) model, we derive and study some cosmological consequences of a varying one-parameter dynamical DE parameterization, which does not allow phantom crossing. We perform a parameter selection using the most recent public available data, such as the data from Planck 2018, eBOSS DR16, Pantheon and KiDS-1000. We find that current observations provide strong constraints on the model parameters, leading to values very close to the $\Lambda$CDM cosmology, at the same time that the well-known $\sigma_8$ tension is reduced from $\sim 3\sigma$ to $\sim 1\sigma$ level.

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R. Marttens, D. Barbosa and J. Alcaniz
Mon, 15 Aug 22
37/54

Comments: 18 pages, 5 figures, LaTeX

Black hole superradiance with (dark) matter accretion [CL]

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http://arxiv.org/abs/2208.06408


Studies of black hole superradiance often focus on the growth of a cloud in isolation, accompanied by the spin-down of the black hole. In this paper, we consider the additional effect of the accretion of matter and angular momentum from the environment. We show that, in many cases, the black hole evolves by drifting along the superradiance threshold, in which case the evolution of its parameters can be described analytically or semi-analytically. We quantify the conditions under which accretion can serve as a mechanism to increase the cloud-to-black hole mass ratio, beyond the standard maximum of about 10%. This occurs by a process we call over-superradiance, whereby accretion effectively feeds the superradiance cloud, by way of the black hole. We give two explicit examples: accretion from a vortex expected in wave dark matter and accretion from a baryonic disk. In the former case, we estimate the accretion rate by using an analytical fit to the asymptotic behavior of the confluent Heun function. Level transition, whereby one cloud level grows while the other shrinks, can be understood in a similar way.

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L. Hui, Y. Law, L. Santoni, et. al.
Mon, 15 Aug 22
41/54

Comments: 29+21 pages, 14 figures

Multiple transitions in vacuum dark energy and $H_0$ tension [CEA]

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http://arxiv.org/abs/2208.05583


We study the effects of multiple transitions in the vacuum dark energy density on the $H_0$ tension problem. We consider a phenomenological model in which the vacuum energy density undergoes multiple transitions in the early as well as the late universe and compare the model’s predictions using the three sets of data from CMB+BAO+SN. The transient dark energy can be either positive (dS-like) or negative (AdS-like). We conclude that a transient late-time AdS-type vacuum energy typically yields the higher value of $H_0$ which can alleviate the $H_0$ tension. In addition, to obtain a value of $H_0$ comparable to the value obtained from the local cosmological measurements the spectral index $n_s$ moves towards its Harrison-Zel’dovich scale invariant value

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H. Moshafi, H. Firouzjahi and A. Talebian
Fri, 12 Aug 22
31/48

Comments: 15 pages, 13 figures

Kinetic Axion $F(R)$ Gravity Inflation [CL]

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http://arxiv.org/abs/2208.05544


In this work we investigate the quantitative effects of the misalignment kinetic axion on $R^2$ inflation. Due to the fact that the kinetic axion possesses a large kinetic energy which dominates its potential energy, during inflation its energy density redshifts as stiff matter fluid and evolves in a constant-roll way, making the second slow-roll index to be non-trivial. At the equations of motion level, the $R^2$ term dominates the evolution, thus the next possible effect of the axion could be found at the cosmological perturbations level, via the second slow-roll index which is non-trivial. As we show, the latter elegantly cancels from the observational indices, however, the kinetic axion extends the duration of the inflationary era to an extent that it may cause a 15$\%$ decrease in the tensor-to-scalar ratio of the vacuum $R^2$ model. This occurs because as the $R^2$ model approaches its unstable quasi-de Sitter attractor in the phase space of $F(R)$ gravity due to the $\langle R^2 \rangle $ fluctuations, the kinetic axion dominates over the $R^2$ inflation and in effect the background equation of state is described by a stiff era, or equivalently a kination era, different from the ordinary radiation domination era. This in turn affects the duration of the inflationary era, increasing the $e$-foldings number up to $5$ $e$-foldings in some cases, depending on the reheating temperature, which in turn has a significant quantitative effect on the observational indices of inflation and especially on the tensor-to-scalar ratio.

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V. Oikonomou
Fri, 12 Aug 22
40/48

Comments: PRD Accepted

Birefringence Tomography for Axion Cloud [CL]

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http://arxiv.org/abs/2208.05724


An axion cloud surrounding a supermassive black hole can be naturally produced through the superradiance process. Its existence can be examined by the axion induced birefringence effect. It predicts an oscillation of the electric vector position angle of linearly polarized radiations. Stringent constraints of the existence of the axion in a particular mass window has been obtained based on the recent Event Horizon Telescope measurement on M87$^\star$. The future Very-Long-Baseline Interferometry (VLBI) observations will be able to measure the vicinity of many supermassive black holes, thus it opens the possibility to search for the existence of axions in a wide mass regime. In this paper, we study how different black hole properties and accretion flows influence the signatures of the axion induced birefringence. We include the impacts of black hole inclination angles, spins, magnetic fields, plasma velocity distributions, the thickness of the accretion flows. We pay special attention to characterize the washout effects induced by the finite thickness of the accretion flows and the lensed photons. Based on this study, we give prospects on how to optimize the axion search using future VLBI observations, such as the next-generation Event Horizon Telescope, to further increase the sensitivity.

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Y. Chen, C. Li, Y. Mizuno, et. al.
Fri, 12 Aug 22
42/48

Comments: 36 pages, 13 figures

Anomalies in Physical Cosmology [CEA]

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http://arxiv.org/abs/2208.05018


The $\Lambda$CDM cosmology passes demanding tests that establish it as a good approximation to reality. The theory is incomplete, of course, and open issues are being examined in active research programs. I offer a review of less widely discussed anomalies that might also point to hints to a still better cosmological theory if more closely examined.

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P. Peebles
Thu, 11 Aug 22
67/68

Comments: A much revised and expanded version of lectures presented in 2021 and earlier and transcribed as arXiv:2106.02672

Listening to Celestial Algebras [CEA]

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http://arxiv.org/abs/2208.05267


In this essay, we immerse into the framework of normed division algebras as a suitable arena to accommodate the standard model of elementary particles, and we explore some applications to cosmology. Remarkably, they permit interesting non-trivial realisations of the cosmological principle with an interplay between the symmetry groups of the quaternions and octonions. We also argue how these realisations give rise to potentially observational signatures in gravitational waves astronomy.

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J. Jiménez and T. Koivisto
Thu, 11 Aug 22
68/68

Comments: 10 pages, 3 figures. Contribution to the special issue Beyond Riemannian Geometry in Classical and Quantum Gravity

Post-Newtonian effects on some characteristic timescales of transiting exoplanets [CL]

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http://arxiv.org/abs/2208.04628


Some measurable characteristic timescales $\left{t_\mathrm{trn}\right}$ of transiting exoplanets are investigated in order to check preliminarily if their cumulative shifts over the years induced by the post-Newtonian (pN) gravitoelectric (Schwarzschild) and gravitomagnetic (Lense-Thirring) components of the stellar gravitational field are, at least in principle, measurable. Both the primary (planet in front of the star) and the secondary (planet behind the star) transits are considered along with their associated characteristic time intervals: the total transit duration $t_D$, the ingress/egress transit duration $\tau$, the full width at half maximum primary transit duration $t_H$, and also the time of conjunction $t_\mathrm{cj}$. For each of them, the net changes per orbit $\langle\Delta t_D\rangle,\,\langle\Delta\tau\rangle,\,\langle\Delta t_H\rangle,\,\langle\Delta t_\mathrm{cj}\rangle$ induced by the aforementioned pN accelerations are analytically obtained; also the Newtonian effect of the star’s quadrupole mass moment $J_2^\star$ is worked out. They are calculated for a fictitious Sun-Jupiter system in an edge-on elliptical orbit, and the results are compared with the present-day experimental accuracies for the HD 286123 b exoplanet. Its pN gravitoelectric shift $\left\langle\Delta t_\mathrm{cj}^\mathrm{1pN}\right\rangle$ may become measurable, at least in principle, at a $\simeq 8\times 10^{-5}$ level of (formal) relative accuracy after about 30 years of continuous monitoring corresponding to about 1000 transits. Systematics like, e.g., confusing time standards, neglecting star spots, neglecting clouds, would likely deteriorate the actual accuracy. The method presented is general enough to be applied also to modified models of gravity.

Read this paper on arXiv…

L. Iorio
Wed, 10 Aug 22
7/66

Comments: LaTex2e, 27 pages, 2 figures, no tables

Post-Newtonian effects on some characteristic timescales of transiting exoplanets [CL]

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http://arxiv.org/abs/2208.04628


Some measurable characteristic timescales $\left{t_\mathrm{trn}\right}$ of transiting exoplanets are investigated in order to check preliminarily if their cumulative shifts over the years induced by the post-Newtonian (pN) gravitoelectric (Schwarzschild) and gravitomagnetic (Lense-Thirring) components of the stellar gravitational field are, at least in principle, measurable. Both the primary (planet in front of the star) and the secondary (planet behind the star) transits are considered along with their associated characteristic time intervals: the total transit duration $t_D$, the ingress/egress transit duration $\tau$, the full width at half maximum primary transit duration $t_H$, and also the time of conjunction $t_\mathrm{cj}$. For each of them, the net changes per orbit $\langle\Delta t_D\rangle,\,\langle\Delta\tau\rangle,\,\langle\Delta t_H\rangle,\,\langle\Delta t_\mathrm{cj}\rangle$ induced by the aforementioned pN accelerations are analytically obtained; also the Newtonian effect of the star’s quadrupole mass moment $J_2^\star$ is worked out. They are calculated for a fictitious Sun-Jupiter system in an edge-on elliptical orbit, and the results are compared with the present-day experimental accuracies for the HD 286123 b exoplanet. Its pN gravitoelectric shift $\left\langle\Delta t_\mathrm{cj}^\mathrm{1pN}\right\rangle$ may become measurable, at least in principle, at a $\simeq 8\times 10^{-5}$ level of (formal) relative accuracy after about 30 years of continuous monitoring corresponding to about 1000 transits. Systematics like, e.g., confusing time standards, neglecting star spots, neglecting clouds, would likely deteriorate the actual accuracy. The method presented is general enough to be applied also to modified models of gravity.

Read this paper on arXiv…

L. Iorio
Wed, 10 Aug 22
39/66

Comments: LaTex2e, 27 pages, 2 figures, no tables

Premerger localization of Intermediate Mass Binary Black Holes with LISA and prospects of joint observations with Athena and LSST [CL]

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http://arxiv.org/abs/2208.03004


The planned Laser Interferometric Space Antenna (LISA) will be able to detect gravitational waves (GWs) from intermediate mass binary black holes (IMBBHs) in the mass range $\sim 10^{2} \mbox{-} 10^{4} M_{\odot}$ up to a redshift $z\sim20$. Modulation effects due to LISA orbital motion around the Sun facilitate precise premerger localization of the sources, which in turn would help in electromagnetic (EM) follow-ups. In this work, we calculate the uncertainties in sky-position, luminosity distance, and time of coalescence as a function of time to coalescence. For representative masses of the IMBBHs, we synthesize a population of binaries uniformly located and oriented on a sphere of radius 3 Gpc and perform parameter estimation using the Fisher information matrix. We find that for systems with a total mass of $10^3 M_{\odot}$, the errors in the sky-position and luminosity distance are $\sim 0.4\,\text{deg}^2$ and $\sim 6\%$, respectively, 1 day prior to coalescence. The coalescence time can be predicted with an uncertainty $\lesssim 10$ sec, 1 day before coalescence. We also find that for $10^3M_{\odot}$, around $40\%$ ($100\%$) of the population has a source localization that is smaller than the field of view of Athena (LSST) 1 day before the merger. These extremely precise measurements can be used to alert ground-based GW detectors and EM telescopes about the time and location of these mergers. We also discuss mechanisms that may produce EM emission from IMBBH mergers and study its detectability using the planned Legacy Survey of Space and Time (LSST) in the optical and Athena in the X-ray bands. Detection of an EM transient may provide us vital clues about the environments where these mergers occur and the distance estimation can pave the way for cosmography.

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P. Saini, S. Bhat and K. Arun
Wed, 10 Aug 22
48/66

Comments: 12 pages, 7 figures

Adaptive Kernel Density Estimation proposal in gravitational wave data analysis [IMA]

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http://arxiv.org/abs/2208.04575


Markov Chain Monte Carlo approach is frequently used within Bayesian framework to sample the target posterior distribution. Its efficiency strongly depends on the proposal used to build the chain. The best jump proposal is the one that closely resembles the unknown target distribution, therefore we suggest an adaptive proposal based on Kernel Density Estimation (KDE). We group parameters of the model according to their correlation and build KDE based on the already accepted points for each group. We adapt the KDE-based proposal until it stabilizes. We argue that such a proposal could be helpful in applications where the data volume is increasing and in the hyper-model sampling. We tested it on several astrophysical datasets (IPTA and LISA) and have shown that in some cases KDE-based proposal also helps to reduce the autocorrelation length of the chains. The efficiency of this proposal is reduces in case of the strong correlations between a large group of parameters.

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M. Falxa, S. Babak and M. Jeune
Wed, 10 Aug 22
62/66

Comments: 12 pages, 11 figures

Characterization of merging black holes with two precessing spins [CL]

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http://arxiv.org/abs/2207.00030


Spin precession in merging black-hole binaries is a treasure trove for both astrophysics and fundamental physics. There are now well-established strategies to infer from gravitational-wave data whether at least one of the two black holes is precessing. In this paper we tackle the next-in-line target, namely the statistical assessment that the observed system has two precessing spins. We find that the recently-developed generalization of the effective precession spin parameter $\chi_\mathrm{p}$ is a well-suited estimator to this task. With this estimator, the occurrence of two precessing spins is a necessary (though not sufficient) condition to obtain values $1<\chi_\mathrm{p}\leq 2$. Confident measurements of gravitational-wave sources with $\chi_\mathrm{p}$ values in this range can be taken as a conservative assessment that the binary presents two precessing spins. We investigate this argument using a large set of >100 software injections assuming anticipated LIGO/Virgo sensitivities for the upcoming fourth observing run, O4. Our results are very encouraging, suggesting that, if such binaries exist in nature and merge at a sufficient rate, current interferometers are likely to deliver the first confident detection of merging black holes with two precessing spins. We investigate prior effects and waveform systemics and, though these need to be better investigated, did not find any confident false-positive case among all the configurations we tested. Our assessment should thus be taken as conservative.

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V. Renzis, D. Gerosa, G. Pratten, et. al.
Mon, 4 Jul 22
18/62

Comments: 11 pages, 7 figures, 1 table

Generating transient noise artifacts in gravitational-wave detector data with generative adversarial networks [IMA]

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http://arxiv.org/abs/2207.00207


Transient noise glitches in gravitational-wave detector data limit the sensitivity of searches and contaminate detected signals. In this Paper, we show how glitches can be simulated using generative adversarial networks. We produce hundreds of synthetic images for the 22 most common types of glitches seen in the LIGO, KAGRA, and Virgo detectors. The artificial glitches can be used to improve the performance of searches and parameter-estimation algorithms. We perform a neural network classification to show that our artificial glitches are an excellent match for real glitches, with an average classification accuracy across all 22 glitch types of 99.0%.

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J. Powell, L. Sun, K. Gereb, et. al.
Mon, 4 Jul 22
28/62

Comments: N/A

The Disordered Heterogeneous Universe: Galaxy Distribution and Clustering Across Length Scales [CEA]

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http://arxiv.org/abs/2207.00519


Studies of disordered heterogeneous media and galaxy cosmology share a common goal: analyzing the distribution of particles at microscales' to predict physical properties atmacroscales’, whether for a liquid, composite material, or entire Universe. The former theory provides an array of techniques to characterize a wide class of microstructures; in this work, we apply them to the distributions of galaxies. We focus on the lower-order correlation functions, void' andparticle’ nearest-neighbor functions, pair-connectedness functions, percolation properties, and a scalar order metric. Compared to homogeneous Poisson and typical disordered systems, the cosmological simulations exhibit enhanced large-scale clustering and longer tails in the nearest-neighbor functions, due to the presence of quasi-long-range correlations. On large scales, the system appears hyperuniform', due to primordial density fluctuations, whilst on the smallest scales, the system becomes almostantihyperuniform’, and, via the order metric, is shown to be a highly correlated disordered system. Via a finite scaling analysis, we show that the percolation threshold of the galaxy catalogs is significantly lower than for Poisson realizations; this is consistent with the observation that the galaxy distribution contains larger voids. However, the two sets of simulations share a fractal dimension, implying that they lie in the same universality class. Finally, we consider the ability of large-scale clustering statistics to constrain cosmological parameters using simulation-based inference. Both the nearest-neighbor distribution and pair-connectedness function considerably tighten bounds on the amplitude of cosmological fluctuations at a level equivalent to observing twenty-five times more galaxies. These are a useful alternative to the three-particle correlation, and are computable in much reduced time. (Abridged)

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O. Philcox and S. Torquato
Mon, 4 Jul 22
30/62

Comments: 27 pages, submitted to Phys. Rev. X

Gravitational Particle Production and the Validity of Effective Descriptions in Loop Quantum Cosmology [CL]

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http://arxiv.org/abs/2207.00435


The effective approach in Loop Quantum Cosmology (LQC) has provided means to obtain predictions for observable quantities in LQC models. While an effective dynamics in LQC has been extensively considered in different scenarios, a robust demonstration of the validity of effective descriptions for the perturbative level still requires further attention. The consistency of the description adopted in most approaches requires the assumption of a test field approximation, which is limited to the cases in which the backreaction of the particles gravitationally produced can be safely neglected. Within the framework of LQC, some of the main approaches to quantize the linear perturbations are the dressed metric, the hybrid approaches and the closed/deformed algebra approach. Here, we analyze the consistency of the test field assumption in these frameworks by computing the energy density stored in the particles gravitationally produced compared to the background energy density. This analysis ultimately provides us with a consistency test of the effective descriptions of LQC.

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G. Vicente, R. Ramos and L. Graef
Mon, 4 Jul 22
32/62

Comments: arXiv admin note: text overlap with arXiv:1812.11191 by other authors

Inferring binary black holes stellar progenitors with gravitational wave sources [CL]

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http://arxiv.org/abs/2207.00374


With its last observing run, the LIGO, Virgo, and KAGRA collaboration has detected almost one hundred gravitational waves from compact binary coalescences. A common approach to studying the population properties of the observed binaries is to use phenomenological models to describe the spin, mass, and redshift distributions. More recently, with the aim of providing a clearer link to astrophysical processes forming the observed compact binaries coalescences, several authors have proposed to employ synthetic catalogs for population studies. In this paper, we review how to employ and interpret synthetic binary catalogs for gravitational-wave progenitors studies. We describe how to build multi-channel merger rates and describe their associated probabilities focusing on stellar progenitor properties. We introduce a method to quantify the match between the phenomenological reconstruction of merger rates with synthetic catalogs. We detail the implementation of synthetic catalogs for multi-channel hierarchical Bayesian inference, highlighting computational aspects and issues related to hyper-prior choice. We find that when inferring stellar progenitors’ properties from gravitational-wave observations, the relative efficiency in compact objects production should be taken into account. Finally, by simulating binary black hole detections with LIGO and Virgo sensitivity expected for the O4 observing run, we present two case studies related to the inference of the common envelope efficiency and progenitor metallicity of the binary black holes. We finally discuss how progenitors’ properties can be linked to binary black hole properties.

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S. Mastrogiovanni, A. Lamberts, R. Srinivasan, et. al.
Mon, 4 Jul 22
35/62

Comments: 13 pages, 12 figures, submitted to MNRAS

Gamma ray burst constraints on cosmological models from the improved Amati correlation [CEA]

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http://arxiv.org/abs/2207.00455


An improved Amati correlation was constructed in (ApJ 931 (2022) 50) by us recently. In this paper, we further study constraints on the $\Lambda$CDM and $w$CDM models from the gamma ray bursts (GRBs) standardized with the standard and improved Amati correlations, respectively. By using the Pantheon type Ia supernova sample to calibrate the latest A220 GRB data set, the GRB Hubble diagram is obtained model-independently. We find that at the high redshift region ($z>1.4$) the GRB distance modulus from the improved Amati correlation is larger apparently than that from the standard Amati one. The GRB data from the standard Amati correlation only give a lower bound limit on the present matter density parameter $\Omega_{\mathrm{m0}}$, while the GRBs from the improved Amati correlation constrain the $\Omega_{\mathrm{m0}}$ with the $68\%$ confidence level to be $0.308^{+0.066}{-0.230}$ and $0.307^{+0.057}{-0.290}$ in the $\Lambda$CDM and $w$CDM models, respectively, which are consistent very well with those given by other current popular observational data including BAO, CMB and so on. Once the $H(z)$ data are added in our analysis, the constraint on the Hubble constant $H_0$ can be achieved. We find that two different correlations provide slightly different $H_0$ results but the marginalized mean values seem to be close to that from the Planck 2018 CMB observations.

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Y. Liu, N. Liang, X. Xie, et. al.
Mon, 4 Jul 22
48/62

Comments: 10 pages, 4 figures, 2 tables. Accepted for publication in ApJ

Initial conditions for the scalaron dark matter [CEA]

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http://arxiv.org/abs/2207.00267


The scalaron of the metric $f(R)$ gravity can constitute dark matter if its mass is in the range $4\,\text{meV} \lesssim m \lesssim 1\,\text{MeV}$. We give an overview of such $f (R)$ gravity theory minimally coupled to the Standard Model. Similarly to other dark-matter models based on scalar fields, this model has the issue of initial conditions. Firstly, the initial conditions for the scalaron are to be tuned in order to produce the observed amount of dark matter. Secondly, the primordial spatial inhomogeneities in the field are to be sufficiently small because they generate entropy (or isocurvature) perturbations, which are constrained by observations. We consider these issues in the present paper. The initial conditions for the scalaron presumably emerge at the inflationary stage. We point out that the homogeneous part of the scalaron initial value is largely unpredictable because of quantum diffusion during inflation. Thus, to account for the observed amount of dark matter, one has to resort to anthropic considerations. Observational constraints on the primordial spatial inhomogeneity of the scalaron are translated into upper bounds on the energy scale of inflation, which happen to be rather weak.

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Y. Shtanov
Mon, 4 Jul 22
51/62

Comments: 20 pages, 1 figure

Higgstory repeats itself [CL]

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http://arxiv.org/abs/2207.00299


We consider a scalar potential with two minima, one of which is arbitrarily deep, such as could be the case for the Higgs potential in the Standard Model. A recent calculation within the thin-wall approximation [arXiv:2205.10240] concludes that regions in which the scalar field takes values beyond the top of the potential barrier are forced by gravity to collapse, while they remain hidden behind a black hole horizon. We show that the thin-wall approximation is not applicable to this problem. We clarify the issue through numerical and analytical solutions to the field equations of the gravity-scalar system. We find that regions around the deeper minimum expand, and would thereby engulf the Universe in post-inflationary cosmology. We also show that black holes with Higgs hair are unstable. Even though the physics of the true vacuum is different, our final conclusion replicates the earlier `Higgstory’ paper [arXiv:1505.04825].

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A. Strumia and N. Tetradis
Mon, 4 Jul 22
53/62

Comments: 21 pages, 7 figures

Emergence of microphysical viscosity in binary neutron star post-merger dynamics [HEAP]

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http://arxiv.org/abs/2207.00442


In nuclear matter in neutron stars the flavor content (e.g., proton fraction) is subject to weak interactions, establishing flavor ($\beta$-)equilibrium. During the merger of two neutron stars there can be deviations from this equilibrium. By incorporating Urca processes into general-relativistic hydrodynamics simulations, we study the resulting out-of-equilibrium dynamics during the collision. We provide the first direct evidence that microphysical transport effects at late times reach a hydrodynamic regime with a nonzero bulk viscosity, making neutron star collisions intrinsically viscous. Finally, we identify signatures of this process in the post-merger gravitational wave emission.

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E. Most, A. Haber, S. Harris, et. al.
Mon, 4 Jul 22
54/62

Comments: N/A

Primordial black hole constraints with Hawking radiation — a review [CEA]

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http://arxiv.org/abs/2206.02672


Primordial black holes are under intense scrutiny since the detection of gravitational waves from mergers of solar-mass black holes in 2015. More recently, the development of numerical tools and the precision observational data have rekindled the effort to constrain the black hole abundance in the lower mass range, that is $M < 10^{23}$g. In particular, primordial black holes of asteroid mass $M \sim 10^{17}-10^{23}\,$g may represent 100\% of dark matter. While the microlensing and stellar disruption constraints on their abundance have been relieved, Hawking radiation of these black holes seems to be the only detection (and constraining) mean. Hawking radiation constraints on primordial black holes date back to the first papers by Hawking. Black holes evaporating in the early universe may have generated the baryon asymmetry, modified big bang nucleosynthesis, distorted the cosmic microwave background, or produced cosmological backgrounds of stable particles such as photons and neutrinos. At the end of their lifetime, exploding primordial black holes would produce high energy cosmic rays that would provide invaluable access to the physics at energies up to the Planck scale. In this review, we describe the main principles of Hawking radiation, which lie at the border of general relativity, quantum mechanics and statistical physics. We then present an up-to-date status of the different constraints on primordial black holes that rely on the evaporation phenomenon, and give, where relevant, prospects for future work. In particular, non-standard black holes and emission of beyond the Standard Model degrees of freedom is currently a hot subject.

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J. Auffinger
Tue, 7 Jun 22
4/70

Comments: 70 pages, 15 figures, invited review submitted for publication to Progress in Particle and Nuclear Physics

The Dipole of the Astrophysical Gravitational-Wave Background [CEA]

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http://arxiv.org/abs/2206.02747


One of the main pillars of the {\Lambda}CDM model is the Cosmological Principle, which states that our Universe is statistically isotropic and homogeneous on large scales. Here we test this hypothesis using the Astrophysical Gravitational Wave Background (AGWB) expected to be measured by the Einstein Telescope-Cosmic Explorer network; in particular we perform a numerical computation of the AGWB dipole, evaluating the intrinsic contribution due to clustering and the kinematic effect induced by the observer motion. We apply a component separation technique in the GW context to disentangle the kinematic dipole, the intrinsic dipole and the shot noise (SN), based on the observation of the AGWB at different frequencies. We show how this technique can also be implemented in matched-filtering to minimize the covariance which accounts for both instrumental noise and SN. Since GW detectors are essentially full-sky, we expect that this powerful tool can help in testing the isotropy of our Universe in the next future.

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L. Dall’Armi, A. Ricciardone and D. Bertacca
Tue, 7 Jun 22
6/70

Comments: 37 pages, 5 figures

Relativistic Mean Field Study of Neutron Stars and Hyperon Stars [CL]

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http://arxiv.org/abs/2206.02202


This thesis focuses on a variety of active research topics, such as nuclear matter, neutron stars, and phase transition within the framework of the RMF model. We use the previously successful effective field theory-driven Relativistic Mean Field (RMF) and density-dependent RMF (DD-RMF)formalisms for analyzing hadron matter to examine the infinite nuclear matter and neutron stars. The presence of exotic phases such as quarks has been investigated using the MIT Bag model and its variants, such as the vBag model, at various bag constants. The other exotic phases, such as hyperons, have also been studied under the influence of a strong magnetic field.

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I. Rather
Tue, 7 Jun 22
15/70

Comments: PhD Thesis

Towards a unified interpretation of the early Universe in $R^2$-corrected dark energy model of $F(R)$ gravity [CL]

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http://arxiv.org/abs/2206.02130


$R^2$-corrected dark energy (DE) models in $F(R)$ gravity have been widely investigated in recent years, which not only removes the weak singularity potentially present in DE models but also provide us with a unified picture of the cosmic history, including the inflationary and DE epochs. Towards the unified interpretation of dynamical DE all over the cosmic history in the class of $R^2$-corrected DE models, we explore the universal features of the scalaron dynamics in the radiation-dominated epoch, along with the chameleon mechanism, by keeping our eyes on the inflationary and DE epochs. We show that the scalaron evolution does not follow a {\it surfing solution} and is mostly adiabatic before big bang nucleosynthesis (BBN), even properly including the {\it kick} by the nonperturbative QCD phase transition, hence a catastrophic consequence claimed in the literature is not applied to this class of DE models. This is due to the presence of the gigantic scale hierarchy between $R^2$ correction and DE, so is the universal feature for the class of $R^2$-corrected DE models. The prospects for the post- or onset-inflationary epoch would be pretty different from what the standard $R^2$ inflationary scenario undergoes due to the presence of the chameleon mechanism.

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H. Chen, T. Katsuragawa and S. Matsuzaki
Tue, 7 Jun 22
18/70

Comments: 23 pages, 10 figures, 1 data file

Inflation, SUSY breaking, and primordial black holes in modified supergravity coupled to chiral matter [CEA]

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http://arxiv.org/abs/2206.02601


We propose a novel model of the modified (Starobinsky-like) old-minimal-type supergravity coupled to a chiral matter superfield, that can {\it simultaneously} describe multi-field inflation, primordial black hole (PBH) formation, dark matter (DM), and spontaneous supersymmetry (SUSY) breaking after inflation in a Minkowski vacuum. The PBH masses in our supergravity model of double slow-roll inflation, with a short phase of “ultra-slow-roll” between two slow-roll phases, are close to $10^{18}$ g. We find that a significant PBH fraction in the allowed mass window requires the very high SUSY breaking scale with the gravitino mass close to the scalaron (inflaton) mass $M$ of the order $10^{13}$ GeV. Our supergravity model favors the {\it composite} nature of DM as a mixture of PBH and heavy gravitinos as the lightest SUSY particles. The composite DM significantly relaxes fine-tuning needed for the whole PBH-DM. The PBH-DM fraction is derived, and the second-order gravitational wave background induced by the enhanced scalar perturbations is calculated. Those gravitational waves may be accessible by the future space-based gravitational interferometers.

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Y. Aldabergenov, A. Addazi and S. Ketov
Tue, 7 Jun 22
19/70

Comments: 27 pages, 14 figures, 7 tables

Black holes, fast scrambling and the breakdown of the equivalence principle [CL]

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http://arxiv.org/abs/2206.02053


Black holes are conjectured to be the fastest quantum scramblers in nature, with the stretched horizon being the scrambling boundary. Under this assumption, we show that any infalling body must couple to virtually the entire black hole Hilbert space even prior to the Page time in order for there to be any hope of preserving the often-cited claim of the equivalence principle that such bodies should experience `no drama’ as they pass a black hole’s horizon. Further, under the scrambling assumption, we recover the usual firewall result at the black hole’s Page time for an initially pure-state black hole without the need for any complexity or computational assumptions. For a black hole that is initially impure, we find that the onset of the firewall is advanced to times prior to the standard Page time. Finally, if black holes really do efficiently scramble quantum information, this suggests that, in order to preserve this claim of the equivalence principle even prior to the onset of a full-blown firewall, the quantum state of a black hole interior must be a Bose-Einstein condensate.

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Z. Wang, S. Das and S. Braunstein
Tue, 7 Jun 22
37/70

Comments: 16 pages, 2 figures

The accurate mass distribution of M87, the Giant Galaxy with imaged shadow of its supermassive black hole, as a portal to new Physics [CEA]

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http://arxiv.org/abs/2206.01997


The very careful Event Horizon Telescope estimate of the mass of the supermassive black hole at the center of the Giant CD galaxy M87, allied with recent high quality photometric and spectroscopic measurements, yields a proper dark/luminous mass decomposition from the galaxy center to its virial radius. That provides us with decisive information on crucial cosmological and astrophysical issues. The dark and the standard matter distributions in a wide first time detected galaxy region under the supermassive black hole gravitational control. The well known supermassive black hole mass vs stellar dispersion velocity relationship at the highest galaxy masses implies an exotic growth of the former. This may be the first case in which one can argue that the supermassive black hole mass growth was also contributed by the Dark Matter component. A huge dark matter halo core in a galaxy with inefficient baryonic feedback is present and consequently constrains the nature of the dark halo particles. The unexplained entanglement between dark/luminous structural properties, already emerged in disk systems, also appears.

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M. Laurentis and P. Salucci
Tue, 7 Jun 22
44/70

Comments: 8 pages, 4 figures, accepted on Apj. Comments welcome

Do we need equation of state in curved spacetime for neutron stars? [CL]

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http://arxiv.org/abs/2206.02106


Neutron star (NS) is regarded as the natural laboratory for nuclear physics. The equation of state (EoS) extracted in flat spacetime is used chronically as an input to the Tolman-Oppenheimer-Volkoff (TOV) equation to constrain the structure of NS. However, using such EoS to characterize the NS with obvious gravitational effect seems controversial. In our work, we demonstrate the EoS of the same nuclear matter, either on earth or inside NS, ought to be in the same form due to the relativity principle. Gravity only enhances the temperature and the chemical potential, known as Tolman’s law and Klein’s law. We also clarify the self-consistency of the TOV equation, i.e., the equilibrium thermodynamics and gravity are included uniformly. The reason for conclusions in JCAP 02, 026 (2021) and Phys. Rev. D 104, 123005 (2021) is that the equilibrium thermodynamic relations protected by the equivalence principle in local spacetime are not taken into account.

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J. Li, T. Guo, J. Zhao, et. al.
Tue, 7 Jun 22
48/70

Comments: 15 pages, 5 figures, 4 tables

Photon ring test of the Kerr hypothesis: variation in the ring shape [HEAP]

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http://arxiv.org/abs/2206.02781


The Event Horizon Telescope (EHT) collaboration recently released horizon-scale images of the supermassive black hole M87*. These images are consistently described by an optically thin, lensed accretion flow in the Kerr spacetime. General relativity (GR) predicts that higher-resolution images of such a flow would present thin, ring-shaped features produced by photons on extremely bent orbits. Recent theoretical work suggests that these “photon rings” produce clear interferometric signatures whose observation could provide a stringent consistency test of the Kerr hypothesis, with scant dependence on the astrophysical configuration. Gralla, Lupsasca and Marrone (GLM) argued that the shape of high-order photon rings follows a specific functional form that is insensitive to the details of the astrophysical source, and proposed an experimental method for measuring this GR-predicted shape via space-based interferometry. We wish to assess the robustness of their prediction by checking that it holds for a variety of astrophysical profiles, black hole spins and observer inclinations. We repeat their analysis for hundreds of models and identify the width of the photon ring and its angular variation as a main obstacle to their method’s success. We qualitatively describe how this width varies with the emission profile, black hole spin and observer inclination. At low inclinations, an improved method is robust enough to confirm the shape prediction for a variety of emission profiles; however, the choice of baseline is critical to the method’s success. At high inclinations, we encounter qualitatively new effects that are caused by the ring’s non-uniform width and require further refinements to the method. We also explore how the photon ring shape could constrain black hole spin and inclination.

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H. Paugnat, A. Lupsasca, F. Vincent, et. al.
Tue, 7 Jun 22
52/70

Comments: 27 pages, 13 figures

Neutrino spin oscillations in gravitational fields in higher dimensions [CL]

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http://arxiv.org/abs/2206.01940


Neutrino physics in one of the most active fields of research with important implications for particle physics, cosmology and astrophysics. On the other hand, motivated by some theories including string theory, formulation of physical theories in more than four space-time dimensions has been the subject of increasing attention in recent years. Interaction of neutrinos with gravitational fields is one of the interesting phenomena which can lead to transition between different helicity states (spin oscillations). We study neutrino spin oscillations in Schwarzschild and RN backgrounds in higher dimensional gravitational fields. We calculate the transition probability as a function of time and also study the dependence of the oscillation frequency on the orbital radius. The results help us to better understand the behavior of gravity and neutrinos in higher dimensions.

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S. Alavi and T. Serish
Tue, 7 Jun 22
61/70

Comments: 13 pages. Comments are welcomed

Hamiltonian Formalism for dynamics of particles in MOG [CL]

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http://arxiv.org/abs/2206.02453


MOG as a modified gravity theory is designed to be replaced with dark matter. In this theory, in addition to the metric tensor, a massive vector is a gravity field where each particle has a charge proportional to the inertial mass and couples to the vector field through the four-velocity of a particle. In this work, we present the Hamiltonian formalism for the dynamics of particles in this theory. The advantage of Hamiltonian formalism is a better understanding and analyzing the dynamics of massive and massless particles. The massive particles deviate from the geodesics of space-time and photons follow the geodesics. We also study the dynamics of particles in the Newtonian and post-Newtonian regimes for observational purposes. An important result of Hamiltonian formalism is that while lensing on large scales is compatible with the observations, however the deflection angle from stellar size lensing is larger than General Relativity. This result can rule out this theory unless we introduce a screening mechanism to change the effective gravitational constant near compact objects like stars.

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S. Rahvar
Tue, 7 Jun 22
62/70

Comments: 5 pages, accepted in Monthly Notices of the Royal Astronomical Society

Constraining Kerr-like black holes with Event Horizon Telescope results of Sgr A* [CL]

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http://arxiv.org/abs/2206.02488


The Event Horizon Telescope (EHT), recently released the image of supermassive black hole Sgr A* showing an angular shadow diameter $d_{sh}= 48.7 \pm 7\,\mu$as, with an inferred black hole mass $M = 4.0^{+1.1}{-0.6} \times 10^6 M\odot $ and Schwarzschild shadow deviation $\delta = -0.08^{+0.09}{-0.09}~\text{(VLTI)},-0.04^{+0.09}{-0.10}~\text{(Keck)}$. The EHT image of Sgr A* is consistent with a Kerr black hole’s expected appearance and the results directly prove a supermassive black hole in the center of the Milky Way. The Kerr hypothesis, a strong-field prediction of general relativity (GR), may not hold in the theories of gravity that admit Kerr-like black holes having an additional deviation parameter arising from the underlying theory. Here, we use the EHT observational results of Sgr A* to investigate the constraints on the deviation parameter whereby, such a rotating Kerr-like black hole can be an astrophysical black hole candidate, paying attention to three leading models. Modelling Kerr-like black holes as supermassive black hole Sgr A*, we observe that for it to be a viable astrophysical black hole candidate, the EHT results of Sgr A* put more stringent constraints on the parameter space than those put by the EHT results of M87*. However, a systematic bias analysis shows Kerr-like black hole shadows may capture Kerr black hole shadows over a good part of the constrained parameter space, making Kerr-like and Kerr black holes indistinguishable and one can’t rule out a possibility of potential modifications of the Kerr metric or GR.

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S. Ghosh and M. Afrin
Tue, 7 Jun 22
69/70

Comments: 13 pages, 4 figures, 1 table

G-constant-roll inflation [CL]

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http://arxiv.org/abs/2206.01264


The constant-roll inflation in the context of Galilean inflation or G-inflation is analyzed. By considering a coupling function $G(\varphi,\chi)\propto g(\varphi)\,\chi^n$ for the model of G-inflation, we find different expressions for a suitable development of a model inflationary in the context of constant roll inflation. In order to obtain analytical solutions, we analyze two specific cases; $g(\varphi)=\varphi$ and $n=0$, i.e., $G(\varphi,\chi)\propto\,\varphi$ and when $g(\varphi)=$ constant and $n=1$ with which $G(\varphi,\chi)\propto\,\chi$. In both cases, we find different expressions for the reconstruction of the background variables and the cosmological perturbations in the framework the constant roll inflation. We utilize recent astronomical observations to constrain the different parameters appearing in the stage of constant roll condition as well in the coupling function $G(\varphi,\chi)$.

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R. Herrera, J. Sadeghi and M. Shokri
Mon, 6 Jun 22
29/41

Comments: 15 pages and 4 figures

Incorporating a radiative hydrodynamics scheme in the numerical-relativity code BAM [CL]

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http://arxiv.org/abs/2206.01337


To study binary neutron star systems and to interpret observational data such as gravitational-wave and kilonova signals, one needs an accurate description of the processes that take place during the final stages of the coalescence, e.g., through numerical-relativity simulations. In this work, we present an updated version of the numerical-relativity code BAM in order to incorporate nuclear-theory based Equations of State and a simple description of neutrino interactions through a Neutrino Leakage Scheme. Different test simulations, for stars undergoing a neutrino-induced gravitational collapse and for binary neutron stars systems, validate our new implementation. For the binary neutron stars systems, we show that we can evolve stably and accurately distinct microphysical models employing the different equations of state: SFHo, DD2, and the hyperonic BHB$\Lambda \phi$. Overall, our test simulations have good agreement with those reported in the literature.

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H. Gieg, F. Schianchi, T. Dietrich, et. al.
Mon, 6 Jun 22
33/41

Comments: 28 pages, 14 figures

The Integrated Sachs-Wolfe Effect in Interacting Dark Matter-Dark Energy Models [CEA]

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http://arxiv.org/abs/2206.01030


Interacting dark matter-dark energy (IDMDE) models can be taken to account as one of the present challenges that may affect the cosmic structures. In this work, we study the integrated Sachs-Wolfe (ISW) effect in IDMDE models. To this end, we initially introduce a theoretical framework for IDMDE models. Moreover, we briefly discuss the stability conditions of IDMDE models and by specifying a simple functional form for the energy density transfer rate, we calculate the perturbation equations. In the following, we calculate the amplitude of the matter power spectrum for the IDMDE model and compare it with the corresponding result obtained from the $\Lambda$CDM model. Furthermore, we calculate the amplitude of the ISW auto-power spectrum as a function of multipole order l for the IDMDE model. The results indicate that the amplitude of the ISW auto-power spectrum in the IDMDE model for different phantom dark energy equations of state behaves similar to the one for the $\Lambda$CDM model, whereas, for the quintessence dark energy equations of state, the amplitude of the ISW-auto power spectrum for the IDMDE model should be higher than the one for the $\Lambda$CDM model. Also, it turns out that the corresponding results by different values of the coupling parameter demonstrate that $\xi$ is inversely proportional to the amplitude of the ISW-auto power spectrum in the IDMDE model. Finally, by employing four different surveys, we calculate the amplitude of the ISW-cross power spectrum as a function of multipole order $l$ for the IDMDE model. The results exhibit that the amplitude of the ISW-cross power spectrum for the IDMDE model for all values of $\omega_{\rm x}$ is higher than the one obtained for the $\Lambda$CDM model. Also, it turns out that the amplitude of the ISW-cross power spectrum in the IDMDE model changes inversely with the value of coupling parameter $\xi$.

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M. Yengejeh, S. Fakhry, J. Firouzjaee, et. al.
Fri, 3 Jun 22
2/57

Comments: 13 pages, 2 tables, 8 figures, references added

Quasinormal modes of Schwarzschild black holes on the real axis [CL]

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http://arxiv.org/abs/2206.00671


We study the scattering of gravitational waves by a Schwarzschild black hole and its perturbed siblings to investigate influences of proposed spectral instability of quasinormal modes on the ringdown signal. Our results indicate that information of dominant ringdown signals, which are ascribed to the fundamental (i.e., least damping) quasinormal mode of unperturbed Schwarzschild black holes, is imprinted in the phase shift defined from the transmission amplitude (1/A_{in} in our notation). This approximately parallels the fact that the resonance of quantum systems is imprinted in the phase shift of the S-matrix. The phase shift around the oscillation frequency of the fundamental mode is modified only perturbatively even if the quasinormal-mode spectrum is destabilized by a perturbative bump at a distant location, signifying the stability of the ringdown signal. At the same time, the phase shift at low frequencies is modulated substantially reflecting the late-time excitation of echo signals associated with the quasinormal-mode spectrum after destabilization.

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K. Kyutoku, H. Motohashi and T. Tanaka
Fri, 3 Jun 22
3/57

Comments: 14 pages, 8 figures

First Constraining Upper Limits on Gravitational Wave Emission from NS 1987A in SNR 1987A [CL]

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http://arxiv.org/abs/2206.01168


We report on a search for continuous gravitational waves (GWs) from NS 1987A, the neutron star born in SN 1987A. The search covered a frequency band of 75-275 Hz, included a wide range of spin-down parameters for the first time, and coherently integrated 12.8 days of data below 125 Hz and 8.7 days of data above 125 Hz from the second Advanced LIGO observing run. We found no astrophysical signal. We set upper limits on GW emission as tight as an intrinsic strain of $2\times10^{-25}$ at 90\% confidence. The large spin-down parameter space makes this search the first astrophysically consistent one for continuous GWs from NS 1987A. Our upper limits are the first consistent ones to beat an analog of the spin-down limit based on the age of the neutron star, and hence are the first GW observations to put new constraints on NS 1987A.

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B. Owen, L. Lindblom and L. Pinheiro
Fri, 3 Jun 22
14/57

Comments: N/A

Assessing the impact of non-Gaussian noise on convolutional neural networks that search for continuous gravitational waves [CL]

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http://arxiv.org/abs/2206.00882


We present a convolutional neural network that is capable of searching for continuous gravitational waves, quasi-monochromatic, persistent signals arising from asymmetrically rotating neutron stars, in $\sim 1$ year of simulated data that is plagued by non-stationary, narrow-band disturbances, i.e., lines. Our network has learned to classify the input strain data into four categories: (1) only Gaussian noise, (2) an astrophysical signal injected into Gaussian noise, (3) a line embedded in Gaussian noise, and (4) an astrophysical signal contaminated by both Gaussian noise and line noise. In our algorithm, different frequencies are treated independently; therefore, our network is robust against sets of evenly-spaced lines, i.e., combs, and we only need to consider perfectly sinusoidal line in this work. We find that our neural network can distinguish between astrophysical signals and lines with high accuracy. In a frequency band without line noise, the sensitivity depth of our network is about $\mathcal{D}^{95\%} \simeq 43.9$ with a false alarm probability of $\sim 0.5\%$, while in the presence of line noise, we can maintain a false alarm probability of $\sim 10\%$ and achieve $\mathcal{D}^\mathrm{95\%} \simeq 3.62$ when the line noise amplitude is $h_0^\mathrm{line}/\sqrt{S_\mathrm{n}(f_k)} = 1.0$. We evaluate the computational cost of our method to be $O(10^{19})$ floating point operations, and compare it to those from standard all-sky searches, putting aside differences between covered parameter spaces. Our results show that our method is more efficient by one or two orders of magnitude than standard searches. Although our neural network takes about $O(10^8)$ sec to employ using our current facilities (a single GPU of GTX1080Ti), we expect that it can be reduced to an acceptable level by utilizing a larger number of improved GPUs.

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T. Yamamoto, A. Miller, M. Sieniawska, et. al.
Fri, 3 Jun 22
17/57

Comments: 17 pages, 11 figures

Looking out for the Galileon in the nanohertz gravitational wave sky [CEA]

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http://arxiv.org/abs/2206.01056


We study the polarizations induced by the Galileon as a stochastic gravitational wave background in the cross correlated power in a pulsar timing array. Working within Galileon gravity, we first show that the scalar gravitational wave signature of the Galileon is encoded solely in its effective mass, which is controlled by the bare mass, conformal coupling, and a tadpole. Then, we study the phenomenology of the Galileon induced scalar polarizations and place observational constraints on these using the present NANOGrav data set. Our results feature longitudinal spatial correlation, indicative of a $10^{-22}$ eV Galileon, and show the Galileon polarizations as more statistically relevant compared with the tranverse tensor ones expected in general relativity.

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R. Bernardo and K. Ng
Fri, 3 Jun 22
18/57

Comments: 5 pages, 2 figures, 1 table, comments welcome

Primordial black hole formation in $F(R)$ bouncing cosmology [CL]

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http://arxiv.org/abs/2206.01150


The phenomenology of primordial black holes (PBHs) physics, and the associated PBH abundance constraints, can be used in order to probe the early-universe evolution. In this work, we focus on the bounce realization within $F(R)$ modified gravity and we investigate the corresponding PBH behavior. In particular, we calculate the energy density power spectrum at horizon crossing time as a function of the involved theoretical parameters, and then we extract the PBH abundance in the context of peak theory, considering the non-linear relation between the density contrast and the comoving curvature perturbation, as well as the critical collapse law for the PBH masses. We first calculate the PBH mass function, and then we extract the PBH abundance $\Omega_\mathrm{PBH,f}$ at formation time as a function of the model parameters, namely the involved $F(R)$ parameter $\alpha$ and the Hubble parameter at the transition time from the bounce to the radiation dominated epoch $H_\mathrm{RD}$. Interestingly, we find that in order to have a significant black hole production, namely $10^{-10}<\Omega_\mathrm{PBH,f}<1$, $H_\mathrm{RD}$ and $\alpha$ should lie roughly within the ranges $10^{-7}M_\mathrm{Pl}\leq H_\mathrm{RD}\leq 10^{-6}M_\mathrm{Pl}$, $10^{-9}M_\mathrm{Pl}\leq H_\mathrm{RD}\leq 2\times 10^{-9}M_\mathrm{Pl}$ and $10^{-30}M^2_\mathrm{Pl}\leq \alpha \leq 10^{-12}M^2_\mathrm{Pl}$ respectively. Finally, we show that the excluded region corresponding to PBH overproduction forms a closed ring.

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S. Banerjee, T. Papanikolaou and E. Saridakis
Fri, 3 Jun 22
20/57

Comments: 20 pages without appendices (27 in total), 6 figures

The energy budget of cosmological first-order phase transitions beyond the bag equation of state [CL]

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http://arxiv.org/abs/2206.01148


The stochastic gravitational-wave backgrounds (SGWBs) from the cosmological first-order phase transitions (FOPTs) serve as a promising probe for the new physics beyond the standard model of particle physics. When most of the bubble walls collide with each other long after they had reached the terminal wall velocity, the dominated contribution to the SGWBs comes from the sound waves characterized by the efficiency factor of inserting the released vacuum energy into the bulk fluid motions. However, the previous works of estimating this efficiency factor have only considered the simplified case of the constant sound velocities in both symmetric and broken phases, either for the bag model with equal sound velocities or $\nu$-model with different sound velocities in the symmetric and broken phases, which is not only unrealistic from a viewpoint of particle physics, but also inconsistent since the sound velocity profile should be solved from the fluid equation of motion (EoM). In this paper, we consistently solve the fluid EoM with the iteration method when taking into account the sound-velocity variation across the bubble wall for a general and realistic equation of state (EoS) beyond the simple bag model and $\nu$-model. We have found a universal suppression effect for the efficiency factor of bulk fluid motions, though such a suppression effect could be negligible for the strong FOPT, in which case the previous estimation from a bag EoS on the efficiency factor of bulk fluid motions still works as a good approximation.

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S. Wang and Z. Yuwen
Fri, 3 Jun 22
25/57

Comments: 30 pages, 8 figures

Effects of a Geometrically Realized Early Dark Energy Era on the Spectrum of Primordial Gravitational Waves [CL]

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http://arxiv.org/abs/2206.00721


In this work we investigate the effects of a geometrically generated early dark energy era on the energy spectrum of the primordial gravitational waves. The early dark energy era, which we choose it to have a constant equation of state parameter $w$, is synergistically generated by an appropriate $f(R)$ gravity in the presence of matter and radiation perfect fluids. As we demonstrate, the predicted signal for the energy spectrum of the $f(R)$ primordial gravitational waves is amplified and can be detectable, for various reheating temperatures, especially for large reheating temperatures. The signal amplitude depends on the duration of the early dark energy era and on the value of the dark energy equation of state parameter, with the most latter affecting more crucially the amplification. Specifically the amplification occurs when the equation of state parameter approaches the de Sitter value $w=-1$. Regarding the duration of the early dark energy era, we find that the largest amplification occurs when the early dark energy era commences at a temperature $T=0.85\,$eV until $T=7.8\,$eV. Moreover we study a similar scenario in which amplification occurs, where the early dark energy era commences at $T=0.29\,$eV and lasts until the temperature is increased by $\Delta T\sim 1.7\,$eV.

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V. Oikonomou and E. Lymperiadou
Fri, 3 Jun 22
52/57

Comments: Accepted in Symmetry, invited article

Probing the rest-frame of the Universe with near-IR cosmic infrared background [CEA]

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http://arxiv.org/abs/2206.00724


While the cosmic microwave background (CMB) dipole is largely assumed entirely kinematic, there appears evidence that a part of it is primordial. Such possibility arises in models implying a tilt, interpreted as a dark flow, across the observable Universe. The kinematic nature of the entire CMB dipole can be probed using the dipole of cosmic backgrounds from galaxies after the last scattering. The near-IR cosmic infrared background (CIB) spectral energy distribution leads to an amplified dipole compared to the CMB. The CIB dipole is affected by galaxy clustering, decreasing with fainter, more distant galaxies, and by Solar System emissions and Galactic dust, which dominate the net CIB cosmological dipole in the optical/near-IR. We propose a technique that enables an accurate measurement of the kinematic near-IR CIB dipole. The CIB, effectively the integrated galaxy light (IGL), would be reconstructed from resolved galaxies in the forthcoming space-borne wide surveys covering four bands 0.9 to 2.5 micron. The galaxies will be sub-selected from the identified magnitude range where the dipole component from galaxy clustering is below the expected kinematic dipole. Using this technique the dipole can be measured in each of the bands at the statistical signal-to-noise S/N>50–100 with the forthcoming Euclid and Roman surveys, isolating CMB dipole’s kinematic nature.

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A. Kashlinsky and F. Atrio-Barandela
Fri, 3 Jun 22
56/57

Comments: MNRAS Letters, in press

A general relativistic estimation of the black hole mass-to-distance ratio at the core of TXS 2226-184 [GA]

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http://arxiv.org/abs/2206.00039


In this work we make use of a general relativistic method to estimate the mass-to-distance ratio M/D = 3.54^{+0.2}{-0.2} X 10^4 M{sun}/Mpc of the black hole hosted at the core of the active galactic nucleus of TXS 2226-184, along with its Right Ascension offset and the recession redshift (velocity) of the galaxy. Our statistical fit is based on the frequency shift of photons emitted by water masers and their orbital positions when circularly revolving around the black hole center within the accretion disk of the active galactic nucleus. By taking into account a previously reported distance to the galaxy, we compare the result of the black hole mass fit to an estimate based on a mass-luminosity correlation. We find that the black hole mass at the core of TXS 2226-184 obtained with the aid of the statistical fit using the general relativistic method, M = 3.67 ^{+0.2}{-0.2} X 10^6 M{sun}, is approximately 0.6 times the black hole mass, M_{BH} = 6.24^{+3.6}{-2.3} X 10^6 M{sun}, computed with the mass-luminosity correlation.

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A. Villalobos-Ramirez, O. Gallardo-Rivera, A. Herrera-Aguilar, et. al.
Thu, 2 Jun 22
6/57

Comments: 7 pages, 3 figures and 2 tables in LaTex format

Signatures of spin precession and nutation in isolated black-hole binaries [HEAP]

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http://arxiv.org/abs/2206.00391


The spin precession of binary black holes (BBHs) that originate from isolated high-mass binary stars is determined by the interplay of phenomena such as tides, winds, accretion, common-envelope evolution, natal kicks, and stellar core-envelope coupling. In previous work, we identified regions of the parameter space that may produce BBHs with large misalignments from natal kicks and high spin magnitudes from three mechanisms – tides, accretion, or inheritance via minimal core-envelope coupling. Here, we explore the spin precession of such BBHs using five parameters that describe the amplitude and frequency with which the orbital angular momentum precesses and nutates about the total angular momentum, modulating the gravitational-wave emission. Precession is generally possible for sufficiently strong natal kicks provided at least one of the black holes is spinning. Nutation is a consequence of spin-spin coupling and depends on the three spin-up mechanisms. Tidal synchronization can leave a distinct correlation between the aligned effective spin and the nutation frequency, but does not produce large nutations. When a black hole accretes $\gtrsim 20\%$ of its companion’s envelope, the precession frequency and amplitude are large. A much smaller amount of accretion, e.g., $\approx 2\%$, is needed to provide a large precession frequency and amplitude when the accretor is a Wolf-Rayet (WR) star. The inheritance of high natal WR spins ($\gtrsim 5\%$ of their maximum breakup value) via minimal core-envelope coupling is the most promising mechanism for producing nutating BBHs, implying that a measurement of nutation from gravitational-wave observations may suggest isolated-binary origin with minimal core-envelope coupling.

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N. Steinle and M. Kesden
Thu, 2 Jun 22
11/57

Comments: N/A

Gravitational scattering of spinning neutrinos by a rotating black hole with a slim magnetized accretion disk [CL]

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http://arxiv.org/abs/2206.00042


We study neutrinos gravitationally scattered off a rotating supermassive black hole which is surrounded by a thin accretion disk with a realistic magnetic field. Neutrinos are supposed to be Dirac particles having a nonzero magnetic moment. Neutrinos, while being scattered, move along arbitrary trajectories not restricted by the equatorial plane. We exactly account for the influence of both gravity and magnetic field on the neutrino motion and its spin evolution. We find the measurable fluxes of outgoing neutrinos taking into account the neutrino spin precession in the external field in curved spacetime. These fluxes turn out to be significantly suppressed for some parameters of the system. Finally, we discuss the possibility to observe the predicted phenomena for core-collapsing supernova neutrinos in our Galaxy.

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M. Dvornikov
Thu, 2 Jun 22
27/57

Comments: 13 pages in LaTeX2e, 7 eps figures

Beyond Einstein's Horizon: Gravitational Condensates and Black Hole Interiors in the Effective Theory of Gravity [CL]

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http://arxiv.org/abs/2206.00139


Two of the most fundamental problems at the nexus of Einstein’s classical General Relativity (GR) and Quantum Field Theory (QFT) are: (1) complete gravitational collapse, presumed in classical GR to lead to a Black Hole (BH) horizon and interior singularity, which generate a number of paradoxes for quantum theory; and (2) the origin and magnitude of the cosmological dark energy driving the accelerated expansion of the Universe.
In this Snowmass white paper it is proposed that these twin puzzles on disparate scales are related, and that their resolution depends upon taking full account of the conformal anomaly of quantum matter in gravitational fields. The topological term in the anomaly leads naturally to the introduction of an abelian $3$-form gauge field, whose field strength can account for a variable gravitational condensate with the vacuum dark energy equation of state $p=-\rho$, the magnitude of which depends upon macroscopic boundary conditions rather than ultraviolet cutoffs. The resulting Effective Field Theory (EFT) of low energy quantum gravity results in a non-singular `BH’ interior and physical surface replacing the classical event horizon, which is a gravitational condensate star free of any information paradox. The development and predictions of this EFT can be tested by gravitational waves and observational cosmology in the coming decade.

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E. Mottola
Thu, 2 Jun 22
29/57

Comments: This white paper submitted to the TF01 category is intended as a sketch of the main ideas of the EFT of gravity addressed also to the broader Snowmass community. The technical details of this EFT are given in arXiv:2205.04703 submitted for publication

The piercing of a boson star by a black hole [CL]

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http://arxiv.org/abs/2206.00021


New light fundamental fields are natural candidates for all or a fraction of dark matter. Self-gravitating structures of such fields might be common objects in the universe, and could comprise even galactic haloes. These structures would interact gravitationally with black holes, process of the utmost importance, since it dictates their lifetime, the black hole motion and possible gravitational radiation emission.
Here, we study the dynamics of a black hole piercing through a much larger fully relativistic boson star, made of a complex minimally coupled massive scalar without self-interactions. As the black hole pierces through the bosonic structure, it is slowed down by accretion and dynamical friction, giving rise to gravitational wave emission. Since we are interested in studying the interaction with large and heavy scalar structures, we consider mass ratios up to $q\sim 10$ and length ratios ${\cal L} \sim 62$.
Somewhat surprisingly, for all our simulations, the black hole accretes more than 95% of the boson star material, even if an initially small black hole collides with large velocity. This is a consequence of an extreme “tidal capture” process, which binds the black hole and the boson star together, for these mass ratios. We find evidence of a “gravitational atom” left behind as a product of the process.

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V. Cardoso, T. Ikeda, Z. Zhong, et. al.
Thu, 2 Jun 22
31/57

Comments: 13 pages, 11 figures, 2 movies in ancillary files. Movies are also available on this https URL

Low frequency tail of gravitational wave spectra from hydromagnetic turbulence [CEA]

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http://arxiv.org/abs/2206.00055


Hydrodynamic and magnetohydrodynamic (MHD) turbulence in the early Universe can drive gravitational waves (GWs) and imprint their spectrum onto that of GWs, which might still be observable today. We study the production of the GW background from freely decaying MHD turbulence for helical and nonhelical initial magnetic fields. To understand the produced GW spectra, we develop a simple model on the basis of the evolution of the magnetic stress tensor. We find that the GW spectra obtained in this model reproduce those obtained in numerical simulations if we consider the time evolution of the low frequency tail of the stress spectrum from numerical simulations. We also show that the shapes of the produced GW frequency spectra are different for helical and nonhelical cases for the same initial magnetic energy spectra. Such differences can help distinguish helical and nonhelical initial magnetic fields from a polarized background of GWs — especially when the expected circular polarization cannot be detected directly.

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R. Sharma and A. Brandenburg
Thu, 2 Jun 22
39/57

Comments: 12 pages, 12 figures, 2 tables

Non-Gaussianity constraints from Planck spectral distortion cross-correlations [CEA]

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http://arxiv.org/abs/2205.15971


Primordial non-Gaussianity can source $\mu$-distortion anisotropies that are correlated with the large-scale temperature and polarization signals of the cosmic microwave background (CMB). A measurement of $\mu T$ and $\mu E$ correlations can therefore be used to constrain it on wavelengths of perturbations not directly probed by the standard CMB anisotropies. In this work, we carry out a first rigorous search for $\mu$-type spectral distortion anisotropies with \Planck data, applying the well-tested constrained ILC component-separation method combined with the needlet framework. We reconstruct a $\mu$ map from \Planck data, which we then correlate with the CMB anisotropies to derive constraints on the amplitude $\fNL$ of the local form bispectrum, specifically on the highly squeezed configurations with effective wavenumbers $k_s \simeq \SI{740}{Mpc^{-1}}$ and $k_L \simeq \SI{0.05}{Mpc^{-1}}$. We improve previously estimated constraints by more than an order of magnitude. This enhancement is owing to the fact that for the first time we are able to use the full multipole information by carefully controlling biases and systematic effects in the final analysis. We also for the first time incorporate constraints from measurements of $\mu E$ correlations, which further tighten the limits. A combination of the derived \Planck $\mu T$ and $\mu E$ power spectra yields $|\fNL| \lesssim 6800$ (95\% c.l.) on this highly squeezed bispectrum. This is only $\simeq 3$ times weaker than the anticipated constraint from \LiteBIRD alone. We show that a combination of \LiteBIRD with \Planck will improve the expected future constraint by $\simeq 20\%$ over \LiteBIRD alone. These limits can be used to constrain multi-field inflation models and primordial black hole formation scenarios, thus providing a promising novel avenue forward in CMB cosmology.

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A. Rotti, A. Ravenni and J. Chluba
Wed, 1 Jun 22
6/65

Comments: Comments welcome. Submitted to MNRAS

$f(R)$-Gravity Generated Post-inflationary Eras and their Effect on Primordial Gravitational Waves [CL]

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http://arxiv.org/abs/2205.15405


In this work we shall consider the effects of a geometrically generated post-inflationary era on the energy spectrum of the primordial gravitational waves. Specifically, we shall consider a post-inflationary constant equation of state era, generated by the synergistic effect of $f(R)$ gravity and of radiation and matter perfect fluids. Two cases of interest shall be studied, one with equation of state parameter $w=-1/3$, in which case the Universe neither accelerates nor decelerates, and one with $w=0$ so an early matter domination era. For the evaluation of the inflationary observational indices which is relevant for the calculation of the gravitational waves energy spectrum, we also took into account the effects of the constant equation of state parameter era, on the $e$-foldings number. In both the $w=-1/3$ and $w=0$ cases, the energy spectrum of the primordial gravitational waves is amplified, but for the $w=0$ case, the effect is stronger.

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V. Oikonomou
Wed, 1 Jun 22
13/65

Comments: Accepted in Annalen de Physik

Uses of Complex Metrics in Cosmology [CL]

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http://arxiv.org/abs/2205.15332


Complex metrics are a double-edged sword: they allow one to replace singular spacetimes, such as those containing a big bang, with regular metrics, yet they can also describe unphysical solutions in which quantum transitions may be more probable than ordinary classical evolution. In the cosmological context, we investigate a criterion proposed by Witten (based on works of Kontsevich & Segal and of Louko & Sorkin) to decide whether a complex metric is allowable or not. Because of the freedom to deform complex metrics using Cauchy’s theorem, deciding whether a metric is allowable in general requires solving a complicated optimisation problem. We describe a method that allows one to quickly determine the allowability of minisuperspace metrics. This enables us to study the off-shell structure of minisuperspace path integrals, which we investigate for various boundary conditions. Classical transitions always reside on the boundary of the domain of allowable metrics, and care must be taken in defining appropriate integration contours for the corresponding gravitational path integral. Perhaps more surprisingly, we find that proposed quantum (`tunnelling’) transitions from a contracting to an expanding universe violate the allowability criterion and may thus be unphysical. No-boundary solutions, by contrast, are found to be allowable, and moreover we demonstrate that with an initial momentum condition an integration contour over allowable metrics may be explicitly described in arbitrary spacetime dimensions.

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C. Jonas, J. Lehners and J. Quintin
Wed, 1 Jun 22
17/65

Comments: 38 pages, 14 figures

Primordial black hole mergers from three-body interactions [CEA]

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http://arxiv.org/abs/2205.15340


Current gravitational-wave observations set the most stringent bounds on the abundance of primordial black holes (PBHs) in the solar mass range. This constraint, however, inherently relies on the merger rate predicted by PBH models. Previous analyses have focused mainly on two binary formation mechanisms: early Universe assembly out of decoupling from the Hubble expansion and dynamical capture in present-day dark matter structures. Using reaction rates of three-body processes studied in the astrophysical context, we show that, under conservative assumptions, three-body interactions in PBH halos efficiently produce binaries and significantly contribute to the overall merger rate, provided PBHs make up a sufficient fraction of the dark matter. Those binaries form at high redshift in Poisson-induced PBH small-scale structures and a fraction is predicted to coalesce and merge within the current age of the Universe, at odds with the dynamical capture scenario where they merge promptly. Our results enable LIGO/Virgo/KAGRA constraints on the PBH abundance to set stronger bounds in this interesting mass range, and have important implications for clustered PBH scenarios that might evade such constraints.

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G. Franciolini, K. Kritos, E. Berti, et. al.
Wed, 1 Jun 22
32/65

Comments: 13 pages, 3 figures

Tidal Love Numbers of Novel and Admixed Celestial Objects [CL]

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http://arxiv.org/abs/2205.15337


A sub-fraction of dark matter or new particles trapped inside celestial objects can significantly alter their macroscopic properties. We investigate the new physics imprint on celestial objects by using a generic framework to solve the Tolman-Oppenheimer-Volkoff (TOV) equations for up to two fluids. We test the impact of populations of new particles on celestial objects, including the sensitivity to self-interaction sizes, new particle mass, and net population mass. Applying our setup to neutron stars and boson stars, we find rich phenomenology for a range of these parameters, including the creation of extended atmospheres. These atmospheres are detectable by their impact on the tidal love number, which can be measured at upcoming gravitational wave experiments such as Advanced LIGO, the Einstein Telescope, and LISA. We release our calculation framework as a publicly available code, allowing the TOV equations to be generically solved for arbitrary new physics models in novel and admixed celestial objects.

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M. Collier, D. Croon and R. Leane
Wed, 1 Jun 22
43/65

Comments: 9 pages, 6 figures. Code available and archived at this https URL

Analytic Modelling of Binary-Single Encounters: Non-Thermal Eccentricity Distribution and Gravitational-Wave Source Formation [HEAP]

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http://arxiv.org/abs/2205.15957


Chaotic three-body interactions may lead to the formation of gravitational-wave sources. Here, by modelling the encounter as a series of close, non-hierarchical, triple approaches, interspersed with hierarchical phases, in which the system consists of an inner binary and a star that orbits it, we compute the pericentre probability distribution, and thereby the in-spiral probability in any given binary-single encounter. We then consider the indirect influence of binary-single encounters on the population of gravitational-wave sources, by changing the eccentricity distribution of hard binaries in clusters; we calculate this distribution analytically, by requiring that it be invariant under interactions with single stars.

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Y. Ginat and H. Perets
Wed, 1 Jun 22
47/65

Comments: Submitted. Comments are welcome

Standardizing reverberation-measured C IV time-lag quasars, and using them with standardized Mg II quasars to constrain cosmological parameters [CEA]

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http://arxiv.org/abs/2205.15552


We use 38 C IV quasar (QSO) reverberation-measured observations, which span eight orders of magnitude in luminosity and the redshift range $0.001064 \leq z \leq 3.368$, to simultaneously constrain cosmological-model and QSO radius-luminosity ($R-L$) relation parameters in six cosmological models, using an improved technique that more correctly accounts for the asymmetric errors bars of the time-lag measurements. We find that $R-L$ relation parameters are independent of the cosmological models used in the analysis and so the $R-L$ relation can be used to standardize the C IV QSOs. The C IV QSO cosmological constraints are consistent with those from Mg II QSOs, allowing us to derive joint C IV + Mg II QSO cosmological constraints which are consistent with currently accelerated cosmological expansion, as well as consistent with cosmological constraints derived using better-established baryon acoustic oscillation (BAO) and Hubble parameter [$H(z)$] measurements. When jointly analyzed with $H(z)$ + BAO data, current C IV + Mg II QSO data mildly tighten current $H(z)$ + BAO data cosmological constraints.

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S. Cao, M. Zajaček, S. Panda, et. al.
Wed, 1 Jun 22
61/65

Comments: 18 pages, 11 figures

Where is the ringdown? Reconstructing quasinormal modes from dispersive waves [CL]

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http://arxiv.org/abs/2205.15878


We study the generation and propagation of gravitational waves in scalar-tensor gravity using numerical relativity simulations of scalar field collapses beyond spherical symmetry. This allows us to compare the tensor and additional massive scalar waves that are excited. As shown in previous work in spherical symmetry, massive propagating scalar waves decay faster than 1/r and disperse, resulting in an inverse chirp. These effects obscure the ringdown in any extracted signal by mixing it with the transient responses of the collapse during propagation. In this paper we present a simple method to rewind the extracted signals to horizon formation, which allows us to clearly identify the ringdown phase and extract the amplitudes of the scalar quasinormal modes, quantifying their excitation in strong gravity events and verifying the frequencies to perturbative calculations. The effects studied are relevant to any theories in which the propagating waves have a dispersion relation, including the tensor case.

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J. Aurrekoetxea, P. Ferreira, K. Clough, et. al.
Wed, 1 Jun 22
62/65

Comments: 10 pages, 8 figures. Movies: this https URL Comments welcome!

A novel ringdown amplitude-phase consistency test [CL]

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http://arxiv.org/abs/2205.14910


The ringdown signal emitted during a binary black hole coalescence can be modeled as a linear superposition of the characteristic damped modes of the remnant black hole that get excited during the merger phase. While checking the consistency of the measured frequencies and damping times against the Kerr BH spectrum predicted by General Relativity~(GR) is a cornerstone of strong-field tests of gravity, the consistency of measured excitation amplitudes and phases have been largely left unexplored. For a nonprecessing, quasi-circular binary black hole merger, we find that GR predicts a narrow region in the space of mode amplitude ratio and phase difference, independently of the spin of the binary components. % Using this unexpected result, we develop a new null test of strong-field gravity which demands that the measured amplitudes and phases of different ringdown modes should lie within this narrow region predicted by GR. We call this the \emph{amplitude-phase consistency test} and introduce a procedure for performing it using information from the ringdown signal. Lastly, we apply this test to the GW190521 event, using the multimodal ringdown parameters inferred by Capano et al.~(2021)~\cite{Capano:2021etf}. While ringdown measurements errors for this event are large, we show that GW190521 is consistent with the amplitude-phase consistency test. Our test is particularly well suited for accommodating multiple loud ringdown detections as those expected in the near future, and can be used complementarily to standard black-hole spectroscopy as a proxy for modified gravity, compact objects other than black holes, and binary precession.

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X. Forteza, S. Bhagwat, S. Kumar, et. al.
Tue, 31 May 22
9/89

Comments: N/A

Compressed Parametric and Non-Parametric Approximations to the Gravitational Wave Likelihood [IMA]

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http://arxiv.org/abs/2205.14154


Gravitational wave observations of quasicircular compact binary mergers imply complicated posterior measurements of their parameters. Though Gaussian approximations to the pertinent likelihoods have decades of history in the field, the relative generality and practical utility of these approximations hasn’t been appreciated, given focus on careful, comprehensive generic Bayesian parameter inference. Building on our previous work in three dimensions, we demonstrate by example that bounded multivariate normal likelihood approximations are accurate, provide useful insight into individual sources and populations, and enable powerful fast calculations which would otherwise be inaccessible for population and low-latency parameter inference. We provide Normal Approximate Likelihood (NAL) fits for each event published in the Gravitational-Wave Transient Catalogs at https://gitlab.com/xevra/nal-data, with public code releases in the near future.

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V. Delfavero, R. O’Shaughnessy, D. Wysocki, et. al.
Tue, 31 May 22
29/89

Comments: N/A

Mountain formation by repeated, inhomogeneous crustal failure in a neutron star [HEAP]

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http://arxiv.org/abs/2205.15026


The elastic crust of a neutron star fractures repeatedly as it spins down electromagnetically. An idealised, macroscopic model of inhomogeneous crustal failure is presented based on a cellular automaton with nearest-neighbour tectonic interactions involving strain redistribution and thermal dissipation. Predictions are made of the size and waiting-time distributions of failure events, as well as the rate of failure as the star spins down. The last failure event typically occurs when the star spins down to approximately 1% of its birth frequency with implications for rotational glitch activity. Neutron stars are commonly suggested as sources of continuous gravitational waves. The output of the automaton is converted into predictions of the star’s mass ellipticity and gravitational wave strain as functions of its age, with implications for future observations with instruments such as the Laser Interferometer Gravitational Wave Observatory (LIGO).

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A. Kerin and A. Melatos
Tue, 31 May 22
30/89

Comments: 18 pages, 18 figures

CMB constraints on monodromy inflation at strong coupling [CEA]

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http://arxiv.org/abs/2205.14952


We carry out a thorough numerical examination of field theory monodromy inflation at strong coupling. We perform an MCMC analysis using a Gaussian likelihood, fitting multiparameter models using CMB constraints on the spectral index and the tensor to scalar ratio. We show that models with uniquely positive Wilson coefficients are ruled out. If there are coefficients that can take on both signs, there can be a cancellation of terms that flattens the potentials and allows one to satisfy current data, and forecasts with strong constraints on the tensor to scalar ratio. Models of field theory monodromy are naturally enhanced to include a mechanism for canceling off radiative corrections to vacuum energy, via vacuum energy sequestering (VES). Although they include a much larger parameter space, we find that a similar numerical examination yields no significant change in the Bayesian evidence for VES enhanced models, with naturalness considerations making them more attractive from a theoretical perspective.

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E. Copeland, F. Cunillera, A. Moss, et. al.
Tue, 31 May 22
32/89

Comments: 23 pages, 8 figures

Study of Asymptotic Velocity in the Bondi-Hoyle Accretion Flows in the Domain of Kerr and 4-D Einstein-Gauss-Bonnet Gravities [HEAP]

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http://arxiv.org/abs/2205.14382


Understanding the physical structures of the accreated matter very close to the black hole in quasars and active galactic nucleus (AGNs) is an important milestone to constrain the activities occurring in their centers. In this paper, we numerically investigate the effects of the asymptotic velocities on the physical structures of the accretion disk around the Kerr and Einstein-Gauss-Bonnet (EGB) rapidly rotating black holes. The Bondi-Hoyle accretion is considered with a falling gas towards the black hole in upstream region of the computational domain. The shock cones are naturally produced in the downstream part of the flow around both black holes. It is found that the structure of the cones and the amount of the accreated matter depend on asymptotic velocity $V_{\infty}$ (Mach number) and the types of the gravities (Kerr or EGB). Increasing the Mach number of the inflowing matter in the supersonic region causes the shock opening angle and accretion rates getting smaller because of the rapidly falling gas towards the black hole. The EGB gravity leads to an increase in the shock opening angle of the shock cones while the mass accretion rates $\dot{M}$ are decreasing in EGB gravity with a Gauss-Bonnet (GB) coupling constant $\alpha$. It is also confirmed that accretion rates and drag forces are significantly altered in the EGB gravity. Our numerical simulation results could be used to identify the accreation mechanism and physical properties of the accretion disk and black hole in the observed $X-$ rays such as NGC $1313$ $X-1$ and $1313$ $X-2$ and MAXI $J1803-298$.

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O. Donmez, F. Dogan and T. Sahin
Tue, 31 May 22
50/89

Comments: 16 pages, 10 figures

Composite pseudo Nambu Goldstone Quintessence [CEA]

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http://arxiv.org/abs/2205.15249


A pseudo-Nambu Goldstone Boson (pNGB) arising from the breaking of a global symmetry ($G\rightarrow H$) can be one of the most sound candidate to describe the thawing quintessence model, which explains the late time acceleration of our universe. Motivated from the Composite Higgs scenario, we have investigated the case where the pNGB associated with $SO(N)/ SO(N-1)$ develops a potential through its couplings with the particles that do not form the complete representations of $G$. The Coleman Weinberg (CW) potential is generated via the external particles in the loop which are linked with the strongly interacting dynamics and can be computed predicatively. The model of Dark Energy (DE) is tested against several latest cosmological observations such as supernovae data of Pantheon, Baryon Acoustic Oscillation (BAO) data, Redshift-space distortion (RSD) data etc. We have found that the fit prefers sub-Planckian value of the pNGB field decay constant. Moreover, we have found that the model predicts cosmological parameters well within the allowed range of the observation and thus gives a well motivated model of quintessence.

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M. Gangopadhyay, N. Kumar, A. Mukherjee, et. al.
Tue, 31 May 22
57/89

Comments: 12 pages, 4 figures, 1 table

Micro-Bose/Proca dark matter stars from black hole superradiance [CL]

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http://arxiv.org/abs/2205.15277


We study the production of heavy, $\mu \gtrsim 1$ TeV, bosonic spin $s=0,1$ dark matter (DM) via the simultaneous processes of Hawking evaporation and superradiance (SR) from an initial population of small, $\lesssim 10^6$ kg, primordial black holes (PBHs). Even for small initial PBH spins the SR process can produce extremely dense gravitationally-bound DM Bose or Proca soliton “stars” of radius $\lesssim {\rm pm}$ and mass $\sim 10^{\rm few}$ kg that can survive to today, well after PBH decay. These solitons can constitute a significant fraction of the DM density, rising to $\gtrsim 50\%$ in the vector DM case.

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J. March-Russell and J. Rosa
Tue, 31 May 22
59/89

Comments: 5 pages, 2 figures

The Inflaton that Could : Primordial Black Holes and Second Order Gravitational Waves from Tachyonic Instability induced in Higgs-$R^2$ Inflation [CL]

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http://arxiv.org/abs/2205.14813


The running of the Higgs self coupling may lead to numerous phenomena in early universe cosmology. In this paper we introduce a scenario where the Higgs running induces turns in the trajectory passing a region with tachyonic mass, leading to a temporal tachyonic growth in the curvature power spectrum. This effect induced by the Higgs leaves phenomena in the form of primordial black holes and stochastic gravitational waves, where proposed GW observatories will be able to probe in the near future.

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D. Cheong, K. Kohri and S. Park
Tue, 31 May 22
62/89

Comments: 21 pages, 9 figures

Exposing Gravitational Waves below the Quantum Shot Noise [CL]

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http://arxiv.org/abs/2205.14197


The sensitivities of ground-based gravitational-wave (GW) detectors are limited by quantum shot noise at a few hundred Hertz and above. Nonetheless, one can use a quantum-correlation technique proposed by Martynov, et al. [Phys. Rev. A 95, 043831 (2017)] to remove the expectation value of the shot noise, thereby exposing underlying classical signals in the cross spectrum formed by cross-correlating the two outputs in a GW interferometer’s anti-symmetric port. We explore here the prospects and analyze the sensitivity of using quantum correlation to detect astrophysical GW signals. Conceptually, this technique is similar to the correlation of two different GW detectors as it utilizes the fact that a GW signal will be correlated in the two outputs but the shot noise will be uncorrelated. Quantum correlation also has its unique advantages as it requires only a single interferometer to make a detection. Therefore, quantum correlation could increase the duty cycle, enhance the search efficiency, and enable the detection of highly polarized signals. In particular, we show that quantum correlation could be especially useful for detecting post-merger remnants of binary neutron stars with both short ($< 1\,{\rm s}$) and intermediate ($\sim 10-10^4\,{\rm s}$) durations and setting upper limits on continuous emissions from unknown pulsars.

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H. Yu, D. Martynov, R. Adhikari, et. al.
Tue, 31 May 22
68/89

Comments: 12 pages, 4 figures, to be submitted to PRD

Horizonless spacetimes as seen by present and next-generation Event Horizon Telescope arrays [HEAP]

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http://arxiv.org/abs/2205.14883


We study the capabilities of present and future radio very-long-baseline-interferometry arrays to distinguish black holes from horizonless spacetimes. We consider an example of a horizonless spacetime, obtained by overspinning a regular black hole. Its image is distinct from the image of a Kerr spacetime due to a second set of photon rings interior to the shadow. These photon rings cannot be directly resolved by present and even next-generation Event Horizon telescope arrays, but instead imprint themselves in horizon-scale images as excess central brightness relative to that of a black hole. We demonstrate that future arrays can detect such indirect imprints.

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A. Eichhorn, R. Gold and A. Held
Tue, 31 May 22
88/89

Comments: 9 pages + references, 5 figures, 3 tables

Black holes in a swirling universe [CL]

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http://arxiv.org/abs/2205.13548


We present a new solution in Einstein’s General Relativity representing a Schwarzschild black hole immersed in a rotating universe. Such a solution is constructed analytically by means of the last unexplored Lie point symmetry of the Ernst equations for stationary and axisymmetric spacetimes. This kind of the Ehlers transformation is able to embed any given solution into a rotating background, which is not of NUT type. We analyse the physical properties, ergoregions and geodesics of the new metric, which is regular outside the event horizon and has a well defined thermodynamics. We finally consider the Kerr generalisation.

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M. Astorino, R. Martelli and A. Viganò
Mon, 30 May 22
1/47

Comments: 19 pages, 11 figures, Mathematica notebook included in the arXiv files

Fundamental physics with ESPRESSO: Constraints on Bekenstein and dark energy models from astrophysical and local probes [CEA]

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http://arxiv.org/abs/2205.13848


Dynamical scalar fields in an effective four-dimensional field theory are naturally expected to couple to the rest of the theory’s degrees of freedom, unless some new symmetry is postulated to suppress these couplings. In particular, a coupling to the electromagnetic sector will lead to spacetime variations of the fine-structure constant, $\alpha$. Astrophysical tests of the space-time stability of $\alpha$ are therefore a powerful probe of new physics. Here we use ESPRESSO and other contemporary measurements of $\alpha$, together with background cosmology data, local laboratory atomic clock and Weak Equivalence Principle measurements, to place stringent constraints on the simplest examples of the two broad classes of varying $\alpha$ models: Bekenstein models and quintessence-type dark energy models, both of which are parametric extensions of the canonical $\Lambda$CDM model. In both cases, previously reported constraints are improved by more than a factor of ten. This improvement is largely due to the very strong local constraints, but astrophysical measurements can help to break degeneracies between cosmology and fundamental physics parameters.

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C. Martins, S. Cristiani, G. Cupani, et. al.
Mon, 30 May 22
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Comments: 8 pages, 2 figures, 2 tables; in press at Phys. Rev. D