Tag Archives: General Relativity and Quantum Cosmology

Light rings and shadows of rotating black holes in the semiclassical gravity with trace anomaly [CL]

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http://arxiv.org/abs/2305.14924


In a recent work by Fernandes [arXiv:2305.10382], an exact stationary and axisymmetric solution was discovered in semiclassical gravity with type-A trace anomaly, identified as a quantum-corrected version of the Kerr black hole. This discovery presents exciting research opportunities for observing non-circular spacetimes. In this study, we explore the light rings and shadow of this black hole solution. Our investigation reveals that there exist prograde and retrograde normal light rings, whose radii increase monotonically with the coupling parameter $\alpha$. We also observe that when $\alpha$ is negative, the shadow area for the quantum-corrected black hole is smaller than that of the Kerr black hole, whereas when $\alpha$ is positive, the area is larger. Furthermore, the NHEKline for nearly extreme black hole disappears when $\alpha$ is greater than zero, while it appears for negative $\alpha$, even if the spin is not too high. Such line sinks in the middle part when $|\alpha|$ is relatively large if $\alpha$ is less than zero.

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Z. Zhang, Y. Hou, M. Guo, et. al.
Thu, 25 May 23
64/64

Comments: 14 pages, 7 figures

The comoving curvature perturbation in Jordan and Einstein frames [CL]

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http://arxiv.org/abs/2305.15326


In the context of $F(\phi)R$ models of gravity, the conformal invariance of the curvature perturbation on the uniform-field slicings has been already demonstrated in several publications. In this work, we study the conformal invariance of the curvature perturbation defined on hypersurfaces that are comoving with an effective fluid. We derive the comoving curvature perturbation in each conformal frame and relate both. It is shown that the conformal invariance of this gauge-invariant curvature perturbation does not always hold, and the analysis on superhorizon and subhorizon scales is performed in the slow-roll regime of inflation. We find that the comoving curvature perturbation is conformally invariant on superhorizon scales but the same cannot be concluded on the subhorizon regime.

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J. Díaz and M. Karčiauskas
Thu, 25 May 23
64/64

Comments: 21 pages

Light rings and shadows of rotating black holes in the semiclassical gravity with trace anomaly [CL]

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http://arxiv.org/abs/2305.14924


In a recent work by Fernandes [arXiv:2305.10382], an exact stationary and axisymmetric solution was discovered in semiclassical gravity with type-A trace anomaly, identified as a quantum-corrected version of the Kerr black hole. This discovery presents exciting research opportunities for observing non-circular spacetimes. In this study, we explore the light rings and shadow of this black hole solution. Our investigation reveals that there exist prograde and retrograde normal light rings, whose radii increase monotonically with the coupling parameter $\alpha$. We also observe that when $\alpha$ is negative, the shadow area for the quantum-corrected black hole is smaller than that of the Kerr black hole, whereas when $\alpha$ is positive, the area is larger. Furthermore, the NHEKline for nearly extreme black hole disappears when $\alpha$ is greater than zero, while it appears for negative $\alpha$, even if the spin is not too high. Such line sinks in the middle part when $|\alpha|$ is relatively large if $\alpha$ is less than zero.

Read this paper on arXiv…

Z. Zhang, Y. Hou, M. Guo, et. al.
Thu, 25 May 23
64/64

Comments: 14 pages, 7 figures

Distinguishing nanohertz gravitational wave sources through the observations of ultracompact minihalos [CEA]

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http://arxiv.org/abs/2305.15100


The common-spectrum process observed by pulsar-timing arrays is interpreted as stochastic gravitational wave backgrounds originating from various sources in the early Universe. Along with generating gravitational waves, we find energy density perturbations also arise with the sources such as bubble collisions and sound waves during first-order phase transitions, cosmic strings, domain walls, condensate fragmentation, and primordial curvature perturbations from inflation. These perturbations can lead to the formation of abundant ultracompact minihalos. Currently, the observational precision is inadequate for discriminating between different models. Then, ongoing and future astrophysical observations of ultracompact minihalos can help to distinguish and constrain the gravitational-wave sources in the nanohertz and $\mu$Hz bands.

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J. Liu
Thu, 25 May 23
64/64

Comments: 7 pages, 1 figure, 1 table

Fast Neutrino Flavor Conversions can Help and Hinder Neutrino-Driven Explosions [HEAP]

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http://arxiv.org/abs/2305.11207


We present the first simulations of core-collapse supernovae (CCSNe) in axial symmetry (2D) with feedback from fast neutrino flavor conversion (FFC). Our schematic treatment of FFCs assumes instantaneous flavor equilibration under the constraint of lepton-number conservation. Systematically varying the spatial domain where FFCs are assumed to occur, we find that they facilitate SN explosions in low-mass (9-12 solar masses) progenitors that otherwise explode with longer time delays, whereas FFCs weaken the tendency to explode of higher-mass (around 20 solar masses) progenitors.

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J. Ehring, S. Abbar, H. Janka, et. al.
Mon, 22 May 23
14/60

Comments: 7 pages, 4 figures, submitted to PRL

Minimal Preheating [CL]

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http://arxiv.org/abs/2305.11246


An oscillating inflaton field induces small amplitude oscillations of the Hubble parameter at the end of inflation. These Hubble parameter induced oscillations, in turn, trigger parametric particle production of all light fields, even if they are not directly coupled to the inflaton. We here study the induced particle production for a light scalar field (e.g. the Standard Model Higgs field) after inflation as a consequence of this effect. Our analysis yields a model-independent lower bound on the efficiency of energy transfer from the inflaton condensate to particle excitations.

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R. Brandenberger, V. Kamali and R. Ramos
Mon, 22 May 23
30/60

Comments: 9 pages, 7 figures

A generalization of photon sphere based on escape/capture cone [CL]

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http://arxiv.org/abs/2305.11208


In asymptotically flat spacetimes, bearing the null geodesics reaching the future null infinity in mind, we propose new concepts, the “dark horizons” as generalizations of the photon sphere. They are defined in terms of the structure of escape/capture cones of photons with respect to a unit timelike vector field. More specifically, considering a two-sphere that represents a set of emission directions of photons, the dark horizons are located at positions where a hemisphere is marginally included in the capture and escape cones, respectively. We show that both of them are absent in the Minkowski spacetime, while they exist in spacetimes with black hole(s) under a certain condition. We derive the general properties of the dark horizons in spherically symmetric spacetimes and explicitly calculate the locations of the dark horizons in the Vaidya spacetime and the Kerr spacetime.

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M. Amo, K. Izumi, H. Yoshino, et. al.
Mon, 22 May 23
38/60

Comments: 34 pages, 11figures

Leading Loops in Cosmological Correlators [CL]

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http://arxiv.org/abs/2305.11228


Cosmological correlators from inflation are often generated at tree level and hence loop contributions are bounded to be small corrections by perturbativity. Here we discuss a scenario where this is not the case. Recently, it has been shown that for any number of scalar fields of any mass, the parity-odd trispectrum of a massless scalar must vanish in the limit of exact scale invariance due to unitarity and the choice of initial state. By carefully handling UV-divergences, we show that the one-loop contribution is non-vanishing and hence leading. Surprisingly, the one-loop parity-odd trispectrum is simply a rational function of kinematics, which we compute explicitly in a series of models, including single-clock inflation. Although the loop contribution is the leading term in the parity-odd sector, its signal-to-noise ratio is typically bounded from above by that of a corresponding tree-level parity-even trispectrum, unless instrumental noise and systematics for the two observables differ. Furthermore, we identify a series of loop contributions to the wavefunction that cancel exactly when computing correlators, suggesting a more general phenomenon.

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M. Lee, C. McCulloch and E. Pajer
Mon, 22 May 23
42/60

Comments: 34 pages, 4 figures

EDGES and JWST with 21cm global signal emulator [CEA]

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http://arxiv.org/abs/2305.11441


The 21cm global signal is an important probe to reveal the properties of the first astrophysical objects and the processes of the structure formation from which one can constrain astrophysical and cosmological parameters. To extract the information of such parameters, one needs to efficiently evaluate the 21cm global signal for statistical analysis. First we developed an artificial neural network-based emulator to predict the 21cm global signal, which works with significantly less computational cost and high precision. Then we apply our emulator to demonstrate the parameter estimation based on the Bayesian analysis by using the publicly available EDGES low-band data. We find that the result is sensitive to the foreground model, the assumption of noise, and the frequency range used in the analysis. The Bayesian evidence suggests the models with higher order polynomial function and enhanced noise are preferred. We also compare models suggested from the EDGES low-band data and the ones from recent JWST measurements of the galaxy luminosity function at $z=16$. We find that the model which produces the 21cm absorption line at $z\approx15$ is well consistent with the central value of the observed luminosity function at $z=16$.

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S. Yoshiura, T. Minoda and T. Takahashi
Mon, 22 May 23
56/60

Comments: 11 pages, 12 figures, 3 tables. Comments welcome

Extreme lensing induces spectro-temporal correlations in black-hole signals [CL]

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http://arxiv.org/abs/2305.11247


Rapid progress in electromagnetic black hole observation presents a theoretical challenge: how can the universal signatures of extreme gravitational lensing be distilled from stochastic astrophysical signals? With this motivation, the two-point correlation function of specific intensity fluctuations across image positions, times, and frequencies is here considered. The contribution of strongly deflected light rays, those which make up the photon ring, is analytically computed for a Kerr black hole illuminated by a simple geometric-statistical emission model. We subsequently integrate over the image to yield a spectro-temporal correlation function which is relevant for unresolved sources. Finally, some observational aspects are discussed and a preliminary assessment of detectability with current and upcoming missions is provided.

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S. Hadar, S. Harikesh and D. Chelouche
Mon, 22 May 23
57/60

Comments: N/A

Cosmic string bursts in LISA [CL]

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http://arxiv.org/abs/2305.11653


Cosmic string cusps are sources of short-lived, linearly polarised gravitational wave bursts which can be searched for in gravitational wave detectors. We assess the capability of LISA to detect these bursts using the latest LISA configuration and operational assumptions. For such short bursts, we verify that LISA can be considered as “frozen”, namely that one can neglect LISA’s orbital motion. We consider two models for the network of cosmic string loops, and estimate that LISA should be able to detect 1-3 bursts per year assuming a string tension $G\mu \approx 10^{-11} – 10^{-10.5}$ and detection threshold $\rm{SNR} \ge 20$. Non-detection of these bursts would constrain the string tension to $G\mu\lesssim 10^{-11}$ for both models.

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P. Auclair, S. Babak, H. Leclere, et. al.
Mon, 22 May 23
60/60

Comments: 6 pages

A novel approach to infer population and cosmological properties with gravitational waves standard sirens and galaxy surveys [CEA]

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http://arxiv.org/abs/2305.10488


Gravitational wave (GW) sources at cosmological distances can be used to probe the expansion rate of the Universe. GWs directly provide a distance estimation of the source but no direct information on its redshift. The optimal scenario to obtain a redshift is through the direct identification of an electromagnetic (EM) counterpart and its host galaxy. With almost 100 GW sources detected without EM counterparts (dark sirens), it is becoming crucial to have statistical techniques able to perform cosmological studies in the absence of EM emission. Currently, only two techniques for dark sirens are used on GW observations: the spectral siren method, which is based on the source-frame mass distribution to estimate conjointly cosmology and the source’s merger rate, and the galaxy survey method, which uses galaxy surveys to assign a probabilistic redshift to the source while fitting cosmology. It has been recognized, however, that these two methods are two sides of the same coin. In this paper, we present a novel approach to unify these two methods. We apply this approach to several observed GW events using the \textsc{glade+} galaxy catalog discussing limiting cases. We provide estimates of the Hubble constant, modified gravity propagation effects, and population properties for binary black holes. We also estimate the binary black hole merger rate per galaxy to be $10^{-6}-10^{-5} {\rm yr^{-1}}$ depending on the galaxy catalog hypotheses.

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S. Mastrogiovanni, D. Laghi, R. Gray, et. al.
Fri, 19 May 23
1/46

Comments: 16 pages, 9 figures

Primordial black holes from null energy condition violation during inflation [CL]

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http://arxiv.org/abs/2305.10933


The violation of the null energy condition (NEC) is closely related to potential solutions for the cosmological singularity problem and may therefore play a crucial role in the very early universe. We explore a novel approach to generate primordial black holes (PBHs) via the violation of the NEC in a single-field inflationary scenario. In our scenario, the universe transitions from a first slow-roll inflation stage with a Hubble parameter H = Hinf1 to a second slow-roll inflation stage with H = Hinf2 > Hinf1, passing through an intermediate stage of NEC violation. The resulting primordial scalar power spectrum is naturally enhanced by the NEC violation at a certain wavelength. As a result, PBHs with masses and abundances of observational interest can be produced in our scenario. We also examine the phenomenological signatures of scalar-induced gravitational waves (SIGWs). Our work highlights the significance of utilizing a combination of PBHs, SIGWs, and primordial gravitational waves as a powerful probe for exploring the NEC violation during inflation.

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Y. Cai, M. Zhu and Y. Piao
Fri, 19 May 23
5/46

Comments: 8 pages, 5 figures

X-Ray Tests of General Relativity with Black Holes [CL]

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http://arxiv.org/abs/2305.10715


General relativity is one of the pillars of modern physics. For decades, the theory has been mainly tested in the weak field regime with experiments in the Solar System and radio observations of binary pulsars. Until 2015, the strong field regime was almost completely unexplored. Thanks to new observational facilities, the situation has dramatically changed in the last few years. Today we have gravitational wave data of the coalesce of stellar-mass compact objects from the LIGO-Virgo-KAGRA Collaboration, images at mm wavelengths of the supermassive black holes in M87$^$ and SgrA$^$ from the Event Horizon Telescope Collaboration, and X-ray data of accreting compact objects from a number of X-ray missions. Gravitational wave tests and black hole imaging tests are certainly more popular and are discussed in other articles of this Special Issue. The aim of the present manuscript is to provide a pedagogical review on X-ray tests of general relativity with black holes and to compare this kind of tests with those possible with gravitational wave data and black hole imaging.

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C. Bambi
Fri, 19 May 23
12/46

Comments: 16 pages, 5 figures. Invited contribution for the Special Issue “Role of Black Holes in Testing Modified Theories of Gravity” for Symmetry (Ed. Rahul Kumar Walia)

Direct mapping of tidal deformability to the iso-scalar and iso-vector nuclear matter parameters [CL]

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http://arxiv.org/abs/2305.11007


Background: The equations of state (EoSs) which determine the properties of neutron stars (NSs) are often characterized by the iso-scalar and iso-vector nuclear matter parameters (NMPs). Recent attempts to relate the radius and tidal deformability of a NS to the individual NMPs have been inconclusive. These properties display strong correlations with the pressure of NS matter which depends on several NMPs. The knowledge of minimal NMPs that determine the NS properties will be necessary to address any connection between NS properties (e.g., tidal deformability) and that of finite nuclei.
Purpose: To identify the important NMPs required to describe the tidal deformability of neutron star for astrophysically relevant range of their gravitational masses (1.2 — 1.8 M$\odot$) as encountered in the binary neutron star merger events.
Method: We construct a large set of EoSs using four iso-scalar and five iso-vector NMPs. These EOSs are employed to perform a systematic analysis to isolate the NMPs that predominantly determine the tidal deformability, over a wide range of NS mass. The tidal deformability is then directly mapped to these NMPs.
Results: The tidal deformability of the NS with mass 1.2-1.8 M$\odot$ can be determined within 10$\%$ directly in terms of four nuclear matter parameters, namely, the incompressibility $K_0$ and skewness $Q_0$ of symmetric nuclear matter, and the slope $L_0$ and curvature parameter $K_{\rm sym,0}$ of symmetry energy.
Conclusion: A function that quickly estimates the value of tidal deformability in terms of minimal nuclear matter parameters is developed. Our method can also be extended to other NS observables.

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S. Imam, A. Mukherjee, B. Agrawal, et. al.
Fri, 19 May 23
24/46

Comments: 5 pages, 5 figures

Up-down binaries are unstable and we want to know [CL]

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http://arxiv.org/abs/2305.10776


The relativistic spin-precession equations for black-hole binaries have four different equilibrium solutions that correspond to systems where the two individual black hole spins are either aligned or anti-aligned with the orbital angular momentum. Surprisingly, it was demonstrated that only three of these equilibrium solutions are stable. Binary systems in the up-down configuration, where the spin of the heavier (lighter) black hole is co- (counter-) aligned with the orbital angular momentum, might be unstable to small perturbations of the spin directions. After the onset of the up-down instability, that occurs after a specific critical orbital separation $r_\mathrm{UD+}$, the binary becomes unstable to spin precession leading to large misalignment of the spins. In this work, we present a Bayesian procedure based on the Savage-Dickey density ratio to test the up-down origin of gravitational-wave events. We apply this procedure to look for promising candidates among the events detected so far during the first three observing runs performed by LIGO/Virgo.

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V. Renzis
Fri, 19 May 23
25/46

Comments: Contribution to the 2023 Gravitation session of the 57th Rencontres de Moriond

Relativistic drag forces on black holes from scalar dark matter clouds of all sizes [CL]

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http://arxiv.org/abs/2305.10492


We use numerical simulations of scalar field dark matter evolving on a moving black hole background to confirm the regime of validity of (semi-)analytic expressions derived from first principles for both dynamical friction and momentum accretion in the relativistic regime. We cover both small and large clouds (relative to the de Broglie wavelength of the scalars), and light and heavy particle masses (relative to the BH size). In the case of a small dark matter cloud, the effect of accretion is a non-negligible contribution to the total force on the black hole, even for small scalar masses. We confirm that this momentum accretion transitions between two regimes (wave- and particle-like) and we identify the mass of the scalar at which the transition between regimes occurs.

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D. Traykova, R. Vicente, K. Clough, et. al.
Fri, 19 May 23
27/46

Comments: 11 pages, 5 figures. Comments welcome!

Parameterized Parity Violation in Gravitational Wave Propagation [CL]

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http://arxiv.org/abs/2305.10478


Gravitational parity violation arises in a variety of theories beyond general relativity. Gravitational waves in such theories have their propagation altered, leading to birefringence effects in both the amplitude and speed of the wave. In this work, we introduce a generalized, theory-motivated parametrization scheme to study parity violation in gravitational wave propagation. This parametrization maps to parity-violating gravity theories in a straightforward way. We find that the amplitude and velocity birefringence effects scale with an effective distance measure that depends on how the dispersion relation is modified. Furthermore, we show that this generic parametrization can be mapped to the parametrized-post-Einsteinian (ppE) formalism with convenient applications to gravitational wave observations and model-agnostic tests of general relativity. We derive a mapping to the standard ppE waveform of the gravitational wave response function, and also find a ppE waveform mapping at the level of the polarization modes, $h_+$ and $h_\times$. Finally, we show how existing constraints in the literature translate to bounds on our new parity-violating parameters and discuss avenues for future analysis.

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L. Jenks, L. Choi, M. Lagos, et. al.
Fri, 19 May 23
31/46

Comments: 19 pages

Gravitational Machines [CL]

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http://arxiv.org/abs/2305.10470


A gravitational machine is defined as an arrangement of gravitating masses from which useful energy can be extracted. It is shown that such machines may exist if the masses are of normal astronomical size. A simple example of a gravitational machine, consisting of a double star with smaller masses orbiting around it, is described. It is shown that an efficient gravitational machine will also be an emitter of gravitational radiation. The emitted radiation sets a limit on the possible performance of gravitational machines, and also provides us with a possible means for detecting such machines if they exist.

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F. Dyson
Fri, 19 May 23
34/46

Comments: 4 pages, one figure

Primordial Black Hole Reheating [CL]

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http://arxiv.org/abs/2305.10518


Post-inflationary reheating phase is usually said to be solely governed by the decay of coherently oscillating inflaton into radiation. In this submission, we explore a new avenue toward reheating through the evaporation of primordial black holes (PBHs). After the inflation, if PBHs form, depending on its initial mass, abundance, and inflaton coupling with the radiation, we found two physically distinct possibilities of reheating the universe. In one possibility, the thermal bath is solely obtained from the decay of PBHs while inflaton plays the role of dominant energy component in the entire process. In the other possibility, we found that PBHs itself dominate the total energy budget of the Universe during the course of evolution, and then its subsequent evaporation leads to radiation dominated universe. Furthermore, we analyze the impact of both monochromatic and extended PBH mass functions and estimate the detailed parameter ranges for which those distinct reheating histories are realized.

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M. Haque, E. Kpatcha, D. Maity, et. al.
Fri, 19 May 23
44/46

Comments: 17 pages, 9 figures

The HI intensity mapping power spectrum: insights from recent measurements [CEA]

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http://arxiv.org/abs/2305.09720


The first direct measurements of the HI intensity mapping power spectrum were recently made using the MeerKAT telescope. These measurements are on nonlinear scales, at redshifts 0.32 and 0.44. We develop a formalism for modelling small-scale power in redshift space, within the context of the mass-weighted HI halo model framework. This model is consistent with the latest findings from surveys on the HI-halo mass relation. In order to model nonlinear scales, we include the 1-halo, shot-noise and finger-of-god effects. Then we apply the model to the MeerKAT auto-correlation data, finding that the model provides a good fit to the data at redshift 0.32, but the data may indicate some evidence for an adjustment at $z \sim 0.44$. Such an adjustment can be achieved by an increase in the HI halo model bias.

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H. Padmanabhan, R. Maartens, O. Umeh, et. al.
Thu, 18 May 23
7/67

Comments: 7 pages, 5 figures

White dwarf cooling in $f(R,T)$ gravity [CL]

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http://arxiv.org/abs/2305.10144


In recent times, astounding observations of both over- and under-luminous type Ia supernovae have emerged. These peculiar observations hint not only at surpassing the Chandrasekhar limit but may also suggest potential modifications in the physical attributes of their progenitors, such as their cooling rate. This, in turn, can influence their temporal assessments and provide a compelling explanation for these intriguing observations. In this spirit, we investigate here the cooling process of white dwarfs in $f(R,T)$ gravity with the simplest model $f(R,T) = R + \lambda T$, where $\lambda$ is the model parameter. Our modelling suggests that the cooling timescale of white dwarfs exhibits an inverse relationship with the model parameter $\lambda$, which implies that for identical initial conditions, white dwarfs in $f(R,T)$ gravity cool faster. This further unveils that in the realm of $f(R,T)$ gravity, the energy release rate for white dwarfs increases as $\lambda$ increases. Furthermore, we also report that the luminosity of the white dwarfs also depends on $\lambda$ and an upswing in $\lambda$ leads to an amplification in the luminosity, and consequently a larger white dwarf in general relativity can exhibit comparable luminosity to a smaller white dwarf in $f(R,T)$ gravity.

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S. Bhattacharjee
Thu, 18 May 23
11/67

Comments: N/A

Bounding the mass of ultralight bosonic Dark Matter particles with the motion of the S2 star around Sgr A* [CL]

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http://arxiv.org/abs/2305.10242


Dark matter is undoubtedly one of the fundamental, albeit unknown, components of the standard cosmological model. The failure to detect WIMPs, the most promising candidate particle for cold dark matter, actually opens the way for the exploration of viable alternatives, of which ultralight bosonic particles with masses $\sim 10^{-21}$ eV represent one of the most encouraging. N-body simulations have shown that such particles form solitonic cores in the innermost parts of virialized galactic halos that are supported by internal quantum pressure on characteristic $\sim$kpc de Broglie scales. In the Galaxy, this halo region can be probed by means of S-stars orbiting the supermassive black hole Sagittarius A* to unveil the presence of such a solitonic core and, ultimately, to bound the boson mass $m_\psi$. Employing a Monte Carlo Markov Chain algorithm, we compare the predicted orbital motion of S2 with publicly available data and set an upper bound $m_\psi \lesssim 3.2\times 10^{-19}$ eV on the boson mass, at 95% confidence level. When combined with other galactic and cosmological probes, our constraints help to reduce the allowed range of the bosonic mass to $(2.0 \lesssim m_\psi \lesssim 32.2)\times 10^{-20}$ eV, at the 95% confidence level, which opens the way to precision measurements of the mass of the ultralight bosonic dark matter.

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R. Monica and I. Martino
Thu, 18 May 23
27/67

Comments: 5 pages, 2 figures, 1 table. Comments are welcome. Additional plot and related code at this http URL

Frequency-domain approach to self-force in hyperbolic scattering [CL]

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http://arxiv.org/abs/2305.09724


We develop a frequency-domain method for calculating the self-force acting on a scalar charge on a fixed scattering geodesic in Schwarzschild spacetime. Existing frequency-domain methods, which are tailored for bound orbits, are inadequate here for several reasons. One must account for the continuous spectrum in the scattering problem, deal with slowly-convergent radial integrals that are hard to evaluate numerically, and confront the inapplicability of the standard self-force method of “extended homogeneous solutions”, which only works for compactly supported sources. We tackle each of these issues in turn, and then present a full numerical implementation, in which we calculate the self-force correction to the scatter angle due to scalar-field back-reaction. We perform a range of internal validation tests, as well as ones based on comparison with existing time-domain results. We discuss the merits and remaining limitations of our method, and outline directions for future work.

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C. Whittall and L. Barack
Thu, 18 May 23
31/67

Comments: 30 pages, 11 figures

End-to-end simulation and analysis pipeline for LISA [IMA]

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http://arxiv.org/abs/2305.09702


The data produced by the future space-based millihertz gravitational-wave detector LISA will require nontrivial pre-processing, which might affect the science results. It is crucial to demonstrate the feasibility of such processing algorithms and assess their performance and impact on the science. We are building an end-to-end pipeline that includes state-of-the-art simulations and noise reduction algorithms. The simulations must include a detailed model of the full measurement chain, capturing the main features that affect the instrument performance and processing algorithms. In particular, we include in these simulations, for the first time, proper relativistic treatment of reference frames with realistic numerically-optimized orbits; a model for onboard clocks and clock synchronization measurements; proper modeling of total laser frequencies, including laser locking, frequency planning and Doppler shifts; and a better treatment of onboard processing. Using these simulated data, we show that our pipeline is able to reduce the most critical noises and form synchronized observables. By injecting signals from a verification binary, we demonstrate that good parameter estimation can be obtained on this more realistic setup, extending existing results from previous LISA Data Challenges.

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B. Jean-Baptiste, H. Olaf, L. Marc, et. al.
Thu, 18 May 23
35/67

Comments: Moriond Gravitation 2023 Proceedings, 7 pages, 5 figures

Gravitational Positivity for Phenomenologists: Dark Gauge Boson in the Swampland [CL]

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http://arxiv.org/abs/2305.10058


The gravitational positivity bound gives quantitative “swampland” constraints on low-energy effective theories inside theories of quantum gravity. We give a comprehensive discussion of this bound for those interested in applications to phenomenological model building. We present a practical recipe for deriving the bound, and discuss subtleties relevant for realistic models. As an illustration, we study the positivity bound on the scattering of the massive gauge bosons in the Higgs/St\”{u}ckelberg mechanism. Under certain assumptions on gravitational amplitudes at high energy, we obtain a lower bound $m_{V} \gtrsim \Lambda_\mathrm{UV}^2 /g M_\mathrm{Pl}$ on the gauge boson mass $m_V$, where $g$ is the coupling constant of the gauge field, $M_\mathrm{Pl}$ is the reduced Planck mass and $\Lambda_\mathrm{UV}$ is the ultraviolet cutoff of the effective field theory. This bound can strongly constrain new physics models involving a massive gauge boson.

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K. Aoki, T. Noumi, R. Saito, et. al.
Thu, 18 May 23
38/67

Comments: 30 pages, 12 figures

Constraints on the spectral signatures of superconducting cosmic strings [CEA]

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http://arxiv.org/abs/2305.09816


If they exist, networks of superconducting cosmic strings are capable of injecting copious amounts of electromagnetic energy into the background over a broad range of frequencies. We study this injection both analytically, as well as numerically using the thermalization code CosmoTherm. With our refined analytic formalism, we update constraints from CMB spectral distortions by following the injection of entropy, as well as energy, on the amplitude of the $\mu$-distortion, leading to a significant improvement in those limits. Furthermore, we utilize the full shape of the distorted spectrum from CosmoTherm to include constraints from non-$\mu$, non-$y$ type distortions. Additionally, we use the outputs for the ionization history and global 21cm signal to derive and update constraints on string model parameters using measurements from other datasets. Analysis of CMB anisotropies provides the most stringent constraints, though with a slightly modified shape and strength when compared to previous results. Modifications of the reionization history provide new bounds in the high current domain, and we also find that the observations of the low-frequency radio background probe a small region of parameter space not explored by other datasets. We also analyze global $21$-cm constraints, and find that the inclusion of soft photon heating plays a crucial role, essentially removing any constraints in the considered parameter domain. Spectral distortion measurements from COBE/FIRAS are covered by other constraints, but our conservative forecast shows that a PIXIE-type satellite would probe important unexplored regions of parameter space.

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B. Cyr, J. Chluba and S. Acharya
Thu, 18 May 23
55/67

Comments: 21 pages, 24 figures, comments welcome!

Black holes that are too cold to respect cosmic censorship [CL]

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http://arxiv.org/abs/2305.08918


In this essay it is proved that there are black holes that are dangerously cold. In particular, by analyzing the emission spectra of highly charged black holes we reveal the fact that near-extremal black holes whose Bekenstein-Hawking temperatures lie in the regime $T_{\text{BH}}\lesssim m^6_e/e^3$ may turn into horizonless naked singularities, thus violating the cosmic censorship principle, if they emit a photon with the characteristic thermal energy $\omega=O(T_{\text{BH}})$ [here ${m_e,e}$ are respectively the proper mass and the electric charge of the electron, the lightest charged particle]. We therefore raise here the conjecture that, in the yet unknown quantum theory of gravity, the temperatures of well behaved black-hole spacetimes are fundamentally bounded from below by the relation $T_{\text{BH}}\gtrsim m^6_e/e^3$.

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S. Hod
Wed, 17 May 23
10/67

Comments: This essay is awarded 4th Prize in the 2023 Essay Competition of the Gravity Research Foundation. 8 pages

Unimodular Proca Theory: Breaking the U(1) gauge symmetry of unimodular gravity via a mass term [CL]

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http://arxiv.org/abs/2305.09380


We study the Hamiltonian structure of unimodular-like theories, where the cosmological constant (or other supposed constants of nature) are demoted from fixed parameters to classical constants of motion. No new local degrees of freedom are present as a result of a $U(1)$ gauge invariance of the theory. Hamiltonian analysis of the action reveals that the only possible gauge fixing that can be enforced is setting the spatial components of the four-volume time vector ${\cal T}^{i}\approx0$. As a consequence of this, the gauge-fixed unimodular path integral is equivalent to the minisuperspace unimodular path integral. However, should we break the $U(1)$ gauge invariance, two things happen: a massless propagating degree of freedom appears, and the (gauge-invariant) zero-mode receives modified dynamics. The implications are investigated, with the phenomenology depending crucially on the target “constant”.

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R. Isichei and J. Magueijo
Wed, 17 May 23
11/67

Comments: N/A

Is there an excess of black holes around $20 M_{\odot}$? Optimising the complexity of population models with the use of reversible jump MCMC [CL]

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http://arxiv.org/abs/2305.08909


Some analyses of the third gravitational wave catalogue released by the LIGO-Virgo-KAGRA collaboration (LVK) suggest an excess of black holes around $15-20 M_{\odot}$. In order to investigate this feature, we introduce two flexible population models, a semi-parametric one and a non-parametric one. Both make use of reversible jump Markov chain Monte-Carlo to optimise their complexity. We also illustrate how the latter can be used to efficiently perform model selection. Our parametric model broadly agrees with the fiducial analysis of the LVK, but finds a peak of events at slightly larger masses. Our non-parametric model shows this same displacement. Moreover, it also suggests the existence of an excess of black holes around $20 M_{\odot}$. We assess the robustness of this prediction by performing mock injections and running hierarchical analyses on those. We find that such a feature might be due to statistical fluctuations, given the small number of events observed so far, with a $5\%$ probability. We estimate that with a few hundreds of observations, as expected for O4, our non-parametric model will, be able to robustly determine the presence of this excess. It will then allow for an efficient agnostic inference of the properties of black holes.

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A. Toubiana, M. Katz and J. Gair
Wed, 17 May 23
18/67

Comments: 8 pages, 6 figures

Identifying Disappearance of a White Dwarf Binary with LISA [HEAP]

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http://arxiv.org/abs/2305.09061


We discuss the prospect of identifying a white dwarf binary merger by monitoring disappearance of its nearly monochromatic gravitational wave. For a ten-year operation of the laser interferometer space antenna (LISA), the chance probability of observing such an event is roughly estimated to be 20%. By simply using short-term coherent signal integrations, we might determine the merger time with an accuracy of $\sim $3-10 days. Also considering its expected sky localizability $\sim0.1$-$ 0.01 {\rm deg^2}$, LISA might make an interesting contribution to the multi-messenger study on a merger event.

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N. Seto
Wed, 17 May 23
20/67

Comments: 6 pages, 1 figure

Cosmology of Single Species Hidden Dark Matter [CEA]

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http://arxiv.org/abs/2305.08943


Cosmology and astrophysics provide various ways to study the properties of dark matter even if they have negligible non-gravitational interactions with the Standard Model particles and remain hidden. We study a type of hidden dark matter model in which the dark matter is completely decoupled from the Standard Model sector except gravitationally, and consists of a single species with a conserved comoving particle number. This category of hidden dark matter includes models that act as warm dark matter but is more general. In particular, in addition to having an independent temperature from the Standard Model sector, it includes cases in which dark matter is in its own thermal equilibrium or is free-streaming, obeys fermionic or bosonic statistics, and processes a chemical potential that controls the particle occupation number. While the usual parameterization using the free-streaming scale or the particle mass no longer applies, we show that all cases can be well approximated by a set of functions parameterized by only one parameter as long as the chemical potential is nonpositive: the characteristic scale factor at the time of the relativistic-to-nonrelativistic transition. We study the constraints from Big Bang Nucleosynthesis, the cosmic microwave background, the Lyman-$\alpha$ forest, and the smallest halo mass. We show that the most significant phenomenological impact is the suppression of the small-scale matter power spectrum — a typical feature when the dark matter has a velocity dispersion or pressure at early times. So far, small dark matter halos provide the strongest constraint, limiting the transition scale factor to be no larger than $\sim1.4\times10^{-4}$ times the scale factor at matter-radiation equality.

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W. Lin, X. Chen, H. Ganjoo, et. al.
Wed, 17 May 23
21/67

Comments: 24 pages, 3 tables, 8 figures, comments welcome

Quasinormal modes and grey-body factors of regular black holes with a scalar hair from the Effective Field Theory [CL]

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http://arxiv.org/abs/2305.09187


The Effective Field Theory (EFT) of perturbations on an arbitrary background geometry with a timelike scalar profile has been recently constructed in the context of scalar-tensor theories. Unlike General Relativity, the regular Hayward metric is realized as an exact background metric in the Effective Field Theory with timelike scalar profile without resorting to special matter field, such as nonlinear electrodynamics. The fundamental quasinormal mode for axial graviational perturbations of this black hole has been considered recently with the help of various methods. Here we make a further step in this direction and find that, unlike the fundamental mode, a few first overtones deviate from their Schwarzschild limit at a much higher rate. This outburst of overtones occurs because the overtones are extremely sensitive to the least change of the near-horizon geometry. The analytical formula for quasinormal modes is obtained in the eikonal regime. In addition, we calculated grey-body factors and showed that regular Hayward black hole with a scalar hair has smaller grey-body factor than the Schwarzschild one. Integration of the wave-like equation in time-domain shows that the power-law tails following the ring-down phase at late times are indistinguishable from the Schwarzschild ones.

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R. Konoplya
Wed, 17 May 23
32/67

Comments: 9 pages, revtex, 3 figures

Extreme mass-ratio inspiral of a spinning body into a Kerr black hole I: Evolution along generic trajectories [CL]

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http://arxiv.org/abs/2305.08919


The study of spinning bodies moving in curved spacetime has relevance to binary black hole systems with large mass ratios, as well as being of formal interest. At zeroth order in a binary’s mass ratio, the smaller body moves on a geodesic of the larger body’s spacetime. Post-geodesic corrections describing forces driving the small body’s worldline away from geodesics must be incorporated to model the system accurately. An important post-geodesic effect is the gravitational self-force, which describes the small body’s interaction with its own spacetime curvature. This effect includes the backreaction due to gravitational-wave emission that leads to the inspiral of the small body into the black hole. When a spinning body orbits a black hole, its spin couples to spacetime curvature. This introduces another post-geodesic correction known as the spin-curvature force. An osculating geodesic integrator that includes both the backreaction due to gravitational waves and spin-curvature forces can be used to generate a spinning-body inspiral. In this paper, we use an osculating geodesic integrator to combine the leading backreaction of gravitational waves with the spin-curvature force. Our analysis only includes the leading orbit-averaged dissipative backreaction, and examines the spin-curvature force to leading order in the small body’s spin. This is sufficient to build generic inspirals of spinning bodies, and serves as a foundation for further work examining how to include secondary spin in large-mass-ratio waveform models.

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L. Drummond, A. Hanselman, D. Becker, et. al.
Wed, 17 May 23
37/67

Comments: 23 pages, 8 figures, submitted to Physical Review D

Primordial black holes and inflation from double-well potentials [CEA]

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http://arxiv.org/abs/2305.09630


We investigate the formation of large peaks in the inflationary curvature power spectrum from double-well potentials. In such scenarios, the initial CMB spectrum is created at large field values. Subsequently, the inflaton will cross one of the minima and will decelerate rapidly as it reaches the local maximum at the origin, either falling back or crossing it. During this final phase, a significant peak in the curvature power spectrum can be generated. Our analysis reveals that this class of models produces more pronounced peaks than the more commonly studied quasi-inflection point scenarios with less tuning for the model parameters. Finally, we construct an explicit theoretically motivated inflationary scenario that is consistent with the latest CMB observations and capable of generating sufficiently large curvature perturbations for primordial black holes.

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A. Karam, N. Koivunen, E. Tomberg, et. al.
Wed, 17 May 23
44/67

Comments: 22 pages, 5 figures

Gradient-Annihilated PINNs for Solving Riemann Problems: Application to Relativistic Hydrodynamics [CL]

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http://arxiv.org/abs/2305.08448


We present a novel methodology based on Physics-Informed Neural Networks (PINNs) for solving systems of partial differential equations admitting discontinuous solutions. Our method, called Gradient-Annihilated PINNs (GA-PINNs), introduces a modified loss function that requires the model to partially ignore high-gradients in the physical variables, achieved by introducing a suitable weighting function. The method relies on a set of hyperparameters that control how gradients are treated in the physical loss and how the activation functions of the neural model are dynamically accounted for. The performance of our GA-PINN model is demonstrated by solving Riemann problems in special relativistic hydrodynamics, extending earlier studies with PINNs in the context of the classical Euler equations. The solutions obtained with our GA-PINN model correctly describe the propagation speeds of discontinuities and sharply capture the associated jumps. We use the relative $l^{2}$ error to compare our results with the exact solution of special relativistic Riemann problems, used as the reference “ground truth”, and with the error obtained with a second-order, central, shock-capturing scheme. In all problems investigated, the accuracy reached by our GA-PINN model is comparable to that obtained with a shock-capturing scheme and significantly higher than that achieved by a baseline PINN algorithm. An additional benefit worth stressing is that our PINN-based approach sidesteps the costly recovery of the primitive variables from the state vector of conserved ones, a well-known drawback of grid-based solutions of the relativistic hydrodynamics equations. Due to its inherent generality and its ability to handle steep gradients, the GA-PINN method discussed could be a valuable tool to model relativistic flows in astrophysics and particle physics, characterized by the prevalence of discontinuous solutions.

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F. Antonio, M. David, R. Roberto, et. al.
Wed, 17 May 23
57/67

Comments: 25 pages, 16 figures

Frequency-Domain Distribution of Astrophysical Gravitational-Wave Backgrounds [CEA]

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http://arxiv.org/abs/2305.09372


The superposition of many astrophysical gravitational waves (GW) signals below typical detection thresholds baths detectors in a stochastic gravitational wave background (SGWB). In this work we present a Fourier space approach to compute the frequency-domain distribution of stochastic gravitational wave backgrounds produced by discrete sources. The expressions for the moment generating function and the distribution of observed (discrete) Fourier modes are provided. The results are then applied to the SGWB originating from the mergers of compact stellar remnants (black holes and neutron stars) in the Universe, which are found to exhibit a $-4$ power-law tail. This tail is verified in the signal-to-noise ratio distribution of GWTC events. Furthermore, the extent to which the subtraction of bright (loud) mergers gaussianizes the resulting confusion noise of unresolved sources is illustrated. The power-law asymptotic tail for the SGWB, and an exponentially decaying tail in the case of the confusion background, are also derived analytically. Our results generalize to any background of gravitational waves emanating from discrete sources.

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Y. Ginat, R. Reischke, I. Rapoport, et. al.
Wed, 17 May 23
58/67

Comments: Comments welcome

On the Decoherence of Primordial Gravitons [CL]

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http://arxiv.org/abs/2305.08071


It is well-known that the primordial scalar curvature and tensor perturbations, $\zeta$ and $\gamma_{ij}$, are conserved on super-horizon scales in minimal inflation models. However, their wave functional has a rapidly oscillating phase which is slow-roll unsuppressed, as can be seen either from boundary (total-derivative) terms of cosmological perturbations, or the WKB approximation of the Wheeler-DeWitt equation. Such an oscillatory phase involves gravitational non-linearity between scalar and tensor perturbations. By tracing out unobserved modes, the oscillatory phase causes faster decoherence of primordial gravitons compared to those by bulk interactions. Our results put a stronger lower bound of decoherence effect to the recent proposals probing squeezed primordial gravitons.

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S. Ning, C. Sou and Y. Wang
Tue, 16 May 23
2/83

Comments: 42 pages, 3 figures, 1 table

Dissipative Inflation via Scalar Production [CL]

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http://arxiv.org/abs/2305.07695


We describe a new mechanism that gives rise to dissipation during cosmic inflation. In the simplest implementation, the mechanism requires the presence of a massive scalar field with a softly-broken global $U(1)$ symmetry, along with the inflaton field. Particle production in this scenario takes place on parametrically sub-horizon scales, at variance with the case of dissipation into gauge fields. Consequently, the backreaction of the produced particles on the inflationary dynamics can be treated in a \textit{local} manner, allowing us to compute their effects analytically. We determine the parametric dependence of the power spectrum which deviates from the usual slow-roll expression. Non-Gaussianities are always sizeable whenever perturbations are generated by the noise induced by dissipation: $f_{\rm NL}^{\rm eq} \gtrsim {O}(10)$.

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P. Creminelli, S. Kumar, B. Salehian, et. al.
Tue, 16 May 23
6/83

Comments: 31 pages + appendices, 8 figures

Dynamics of false vacuum bubbles with trapped particles [CL]

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http://arxiv.org/abs/2305.07702


We study the impact of the ambient fluid on the evolution of collapsing false vacuum bubbles by simulating the dynamics of a coupled bubble-particle system. A significant increase in the mass of the particles across the bubble wall leads to a buildup of those particles inside the false vacuum bubble. We show that the backreaction of the particles on the bubble slows or even reverses the collapse. Consequently, if the particles in the true vacuum become heavier than in the false vacuum, the particle-wall interactions always decrease the compactness that the false vacuum bubbles can reach making their collapse to black holes less likely.

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M. Lewicki, K. Müürsepp, J. Pata, et. al.
Tue, 16 May 23
17/83

Comments: 13 pages, 7 figures

Extinction biases quasar luminosity distances determined from quasar UV and X-ray flux measurements [GA]

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http://arxiv.org/abs/2305.08179


A sample of X-ray detected reverberation-mapped quasars provides a unique opportunity to compare cosmological constraints inferred using two well-established relations – the X-ray/UV luminosity ($L_{X}-L_{UV}$) relation and the broad-line region radius-UV monochromatic luminosity ($R-L$) relation. $L_{X}-L_{UV}$ and $R-L$ luminosity distances to the same quasars exhibit a distribution of their differences that is generally positively skewed for the six cosmological models we consider. This behaviour can be interpreted qualitatively to arise as a result of the dust extinction of UV/X-ray quasar emission. We show that the extinction always contributes to the non-zero difference between $L_{X}-L_{UV}$-based and $R-L$-based luminosity distances and we derive a linear relationship between the X-ray/UV colour index $E_{X-UV}$ and the median/mean value of the luminosity-distance difference, which also depends on the value of the $L_{X}-L_{UV}$ relation slope. Taking into account the prevailing positive values of the luminosity-distance difference median, we estimate an average X-ray/UV colour index of $\overline{E}{X-UV}=0.089 \pm 0.019$ mag, while the value based on the positive mean values of the difference is $\overline{E}{X-UV}=0.050\pm 0.013$ mag. We demonstrate that this amount of extinction is typical for the majority of quasars since it originates in the circumnuclear and interstellar media of host galaxies. It can only be slightly alleviated by the standard hard X-ray and far-UV extinction cuts used by Lusso et al. (2020). Consequently, the $L_{X}-L_{UV}$ relation QSO data compilation of Lusso et al. (2020) cannot be used for cosmological purposes.

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M. Zajaček, B. Czerny, N. Khadka, et. al.
Tue, 16 May 23
19/83

Comments: 12 pages, 7 figures, 3 tables; submitted to the MNRAS Main Journal, comments welcome

QoQ: a Q-transform based test for Gravitational Wave transient events [CL]

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http://arxiv.org/abs/2305.08257


The observation of transient gravitational waves is hindered by the presence of transient noise, colloquially referred to as glitches. These glitches can often be misidentified as gravitational waves by searches for unmodeled transients using the excess-power type of methods and sometimes even excite template waveforms for compact binary coalescences while using matched filter techniques. They thus create a significant background in the searches. This background is more critical in getting identified promptly and efficiently within the context of real-time searches for gravitational-wave transients. Such searches are the ones that have enabled multi-messenger astrophysics with the start of the Advanced LIGO and Advanced Virgo data taking in 2015 and they will continue to enable the field for further discoveries. With this work we propose and demonstrate the use of a signal-based test that quantifies the fidelity of the time-frequency decomposition of the putative signal based on first principles on how astrophysical transients are expected to be registered in the detectors and empirically measuring the instrumental noise. It is based on the Q-transform and a measure of the occupancy of the corresponding time-frequency pixels over select time-frequency volumes; we call it “QoQ”. Our method shows a 40% reduction in the number of retraction of public alerts that were issued by the LIGO-Virgo-KAGRA collaborations during the third observing run with negligible loss in sensitivity. Receiver Operator Characteristic measurements suggest the method can be used in online and offline searches for transients, reducing their background significantly.

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S. Soni, E. Marx, E. Katsavounidis, et. al.
Tue, 16 May 23
25/83

Comments: 39 Figures, 5 Tables

Two-body problem in theories with kinetic screening [CL]

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http://arxiv.org/abs/2305.07725


New light scalar degrees of freedom may alleviate the dark matter and dark energy problems, but if coupled to matter, they generally mediate a fifth force. In order for this fifth force to be consistent with existing constraints, it must be suppressed close to matter sources, e.g. through a non-linear screening mechanism. In this work, we investigate the non-relativistic two-body problem in shift-symmetric scalar-tensor theories that exhibit kinetic screening ($k$-mouflage), both numerically and analytically. We develop an approximate scheme, based on a Hodge-Helmholtz decomposition of the Noether current associated to the shift symmetry, allowing for a qualitative insight into the dynamics and yielding results in good agreement with the numerical ones in most of the parameter space. We apply the formalism to polynomial $k$-essence and to Dirac-Born-Infeld (DBI) type theories, as well as to theories that develop “anti-screening”. In the deep nonlinear regime, we find that the fifth force is screened slightly more efficiently in equal-mass systems than in extreme mass-ratio ones. However, we find that systems with comparable masses also exhibit regions where the screening is ineffective. These descreened spheroidal regions (bubbles) could in principle be probed in the solar system with sufficiently precise space accelerometers.

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M. Bošković and E. Barausse
Tue, 16 May 23
28/83

Comments: 16+5 pages; 13 figures

A Novel Cosmological Joint Constraints in Multidimensional Observables Space with Redshift-free Inferences [CEA]

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http://arxiv.org/abs/2305.08047


Cosmology constraints serve as a crucial criterion in discriminating cosmological models. The traditional combined method to constrain the cosmological parameters designates the corresponding theoretical value and observational data as functions of redshift, however, sometimes the redshift cannot be measured directly, or the measurement error is large, or the definition of redshift is controversial. In this paper, we propose a novel joint method to constrain parameters that eliminates the redshift $z$ and makes full use of the multiple observables $\left\lbrace \mathcal{F}{1,\mathrm{obs}},\mathcal{F}{2,\mathrm{obs}},\cdots,\mathcal{F}{M,\mathrm{obs}}\right\rbrace$ spanning in $M$-dimensional joint observables space. Considering the generality of the mathematical form of the cosmological models and the guidance from low to high dimensions, we firstly validate our method in a three-dimensional joint observables space spanned by $H(z)$, $f\sigma{8}(z)$ and $D_{A}(z)$, where the three coordinates can be considered redshift-free measurements of the same celestial body (or shared-redshift data reconstructed model independently). Our results are consistent with the traditional combined method but with lower errors, yielding $H_0=68.7\pm0.1\mathrm{~km} \mathrm{~s}^{-1}\mathrm{~Mpc}^{-1}$, $\Omega_{m0}=0.289\pm0.003$, $\sigma_{8}=0.82\pm0.01$ and showing alleviated parametric degeneracies to some extent. In principle, our joint constraint method allows an extended form keeping the redshift information as an independent coordinate and can also be readily degraded to the form of a traditional combined method to constrain parameters.

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W. Hong, K. Jiao, Y. Wang, et. al.
Tue, 16 May 23
33/83

Comments: 16 pages, 12 figures, 4 tables, Submitted to Astrophysical Journal Supplement

Role of Future SNIa Data from LSST in Reinvestigating Cosmological Models [CEA]

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http://arxiv.org/abs/2305.08786


We study how future Type-Ia supernovae (SNIa) standard candles detected by the Vera C. Rubin Observatory (LSST) can constrain some cosmological models. We use a realistic three-year SNIa simulated dataset generated by the LSST Dark Energy Science Collaboration (DESC) Time Domain pipeline, which includes a mix of spectroscopic and photometrically identified candidates. We combine this data with Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation (BAO) measurements to estimate the dark energy model parameters for two models- the baseline $\Lambda$CDM and Chevallier-Polarski-Linder (CPL) dark energy parametrization. We compare them with the current constraints obtained from joint analysis of the latest real data from the Pantheon SNIa compilation, CMB from Planck 2018 and BAO. Our analysis finds tighter constraints on the model parameters along with a significant reduction of correlation between $H_0$ and $\sigma_8$. We find that LSST is expected to significantly improve upon the existing SNIa data in the critical analysis of cosmological models.

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R. Shah, A. Mitra, P. Mukherjee, et. al.
Tue, 16 May 23
34/83

Comments: 8 pages, 5 figures

Abnormal light signals and the underdetermination of theory by evidence in astrophysics [CL]

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http://arxiv.org/abs/2305.08666


We investigate the propagation of certain non-plane wave solutions to Maxwell’s equations in both flat and curved spacetimes. We find that the effective signal velocity associated to such solutions need not be $c$ and that the signal need not propagate along null geodesics; indeed, more than this, we find that the information encoded in the signals associated with such solutions can be substantially non-local. Having established these results, we then turn to their conceptual-philosophical-foundational significance — which, in brief, we take to be the following: (i) one should not assume that all electromagnetic waves generated in the cosmos are localised plane wave packages; thus, (ii) one cannot assume that signals reaching us from the cosmos arrive with a particular velocity (namely, $c$), and that such signals encode local information regarding their sources; therefore (iii) astrophysicists and cosmologists should be wary about making such assumptions in their inferences from obtained data — for to do so may lead to incorrect inferences regarding the nature of our universe.

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F. Asenjo, S. Hojman, N. Linnemann, et. al.
Tue, 16 May 23
42/83

Comments: 16 pages, 4 figures, critical feedback welcome

Pulsar timing residual induced by ultralight tensor dark matter [CL]

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http://arxiv.org/abs/2305.08091


Ultralight boson fields, with a mass around $10^{-23}\text{eV}$, are promising candidates for the elusive cosmological dark matter. These fields induce a periodic oscillation of the spacetime metric in the nanohertz frequency band, which is detectable by pulsar timing arrays. In this paper, we investigate the gravitational effect of ultralight tensor dark matter on the arrival time of radio pulses from pulsars. We find that the pulsar timing signal caused by tensor dark matter exhibits a different angular dependence than that by scalar and vector dark matter, making it possible to distinguish the ultralight dark matter signal with different spins. Combining the gravitational effect and the coupling effect of ultralight tensor dark matter with standard model matter provides a complementary way to constrain the coupling parameter $\alpha$. We estimate $\alpha \lesssim 10^{-6}\sim 10^{-5}$ in the mass range $m<5\times 10^{-23}\mathrm{eV}$ with current pulsar timing array.

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Y. Wu, Z. Chen and Q. Huang
Tue, 16 May 23
45/83

Comments: 12 pages, 3 figures

Resolving phase transition properties of dense matter through tidal-excited g-mode from inspiring neutron stars [CL]

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http://arxiv.org/abs/2305.08401


The investigation of the phase state of dense matter is hindered by complications of first-principle nonperturbative quantum chromodynamics. By performing the first consistent general-relativistic calculations of tidal-excited g-mode of neutron stars with a first-order strong interaction phase transition in the high-density core, we demonstrate that gravitational wave signal during binary neutron star inspiral probes their innermost hadron-quark transition and provides potent constraints from present and future gravitational-wave detectors.

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Z. Miao, E. Zhou and A. Li
Tue, 16 May 23
51/83

Comments: 5 pages, 3 figures, 6 pages supplemental material

Multi-messenger observations of core-collapse supernovae: Exploiting the standing accretion shock instability [HEAP]

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http://arxiv.org/abs/2305.07688


The gravitational wave (GW) and neutrino signals from core-collapse supernovae (CCSNe) are expected to carry pronounced imprints of the standing accretion shock instability (SASI). We investigate whether the correlation between the SASI signatures in the GW and neutrino signals could be exploited to enhance the detection efficiency of GWs. We rely on a benchmark full-scale three-dimensional CCSN simulation with zero-age main sequence mass of $27\ M_\odot$. Two search strategies are explored: 1.~the inference of the SASI frequency range and/or time window from the neutrino event rate detectable at the IceCube Neutrino Observatory; 2.~the use of the neutrino event rate to build a matched filter template. We find that incorporating information from the SASI modulations of the IceCube neutrino event rate can increase the detection efficiency compared to standard GW excess energy searches up to $30\%$ for nearby CCSNe. However, we do not find significant improvements in the overall GW detection efficiency for CCSNe more distant than $1.5$~kpc. We demonstrate that the matched filter approach performs better than the unmodeled search method, which relies on a frequency bandpass inferred from the neutrino signal. The improved detection efficiency provided by our matched filter method calls for additional work to outline the best strategy for the first GW detection from CCSNe.

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M. Drago, H. Andresen, I. Palma, et. al.
Tue, 16 May 23
63/83

Comments: N/A

The Two Quasi-Static Limits of Aether Scalar Tensor Theory [CL]

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http://arxiv.org/abs/2305.07742


One of the aims of Aether Scalar Tensor Theory (AeST) is to reproduce the successes of Modified Newtonian Dynamics (MOND) on galactic scales. Indeed, the quasi-static limit of AeST can achieve precisely this, assuming that the vector field $\vec{A}$ vanishes. However, this assumption of a vanishing vector field is often inconsistent. Here, we show how to correctly take into account the vector field and find that the quasi-static limit depends on a model parameter $m_\times$. In the limit $m_\times \to 0$, one recovers the quasi-static limit with a vanishing vector field. In particular, one finds a two-field version of MOND. In the opposite limit, $m_\times \to \infty$, one finds a single-field version of MOND. We show that, in practice, much of the phenomenology of the quasi-static limit depends only very little on the value of $m_\times$. Still, for some observational tests, such as those involving wide binaries, $m_\times$ has percent-level effects that may be important.

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T. Mistele
Tue, 16 May 23
80/83

Comments: 24 pages, 4 figures

Dynamic Dark Energy from the Local Limit of Nonlocal Gravity [CL]

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http://arxiv.org/abs/2305.07630


Nonlocal gravity (NLG), a classical extension of Einstein’s theory of gravitation, has been studied mainly in linearized form. In particular, nonlinearities have thus far prevented the treatment of cosmological models in NLG. In this essay, we discuss the local limit of NLG and apply this limit to the expanding homogenous and isotropic universe. The theory only allows spatially flat cosmological models; furthermore, de Sitter spacetime is forbidden. The components of the model will have different dynamics with respect to cosmic time as compared to the standard $\Lambda$CDM model; specifically, instead of the cosmological constant, the modified flat model of cosmology involves a dynamic dark energy component in order to account for the accelerated phase of the expansion of the universe.

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J. Tabatabaei, A. Banihashemi, S. Baghram, et. al.
Mon, 15 May 23
3/53

Comments: Honorable Mention in the Gravity Research Foundation 2023 Awards for Essays on Gravitation

Dynamic Dark Energy from the Local Limit of Nonlocal Gravity [CL]

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http://arxiv.org/abs/2305.07630


Nonlocal gravity (NLG), a classical extension of Einstein’s theory of gravitation, has been studied mainly in linearized form. In particular, nonlinearities have thus far prevented the treatment of cosmological models in NLG. In this essay, we discuss the local limit of NLG and apply this limit to the expanding homogenous and isotropic universe. The theory only allows spatially flat cosmological models; furthermore, de Sitter spacetime is forbidden. The components of the model will have different dynamics with respect to cosmic time as compared to the standard $\Lambda$CDM model; specifically, instead of the cosmological constant, the modified flat model of cosmology involves a dynamic dark energy component in order to account for the accelerated phase of the expansion of the universe.

Read this paper on arXiv…

J. Tabatabaei, A. Banihashemi, S. Baghram, et. al.
Mon, 15 May 23
3/53

Comments: Honorable Mention in the Gravity Research Foundation 2023 Awards for Essays on Gravitation

Searches for continuous gravitational waves from neutron stars: A twenty-year retrospective [CL]

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http://arxiv.org/abs/2305.07106


Seven years after the first direct detection of gravitational waves, from the collision of two black holes, the field of gravitational wave astronomy is firmly established. A first detection of continuous gravitational waves from rapidly-spinning neutron stars could be the field’s next big discovery. I review the last twenty years of efforts to detect continuous gravitational waves using the LIGO and Virgo gravitational wave detectors. I summarise the model of a continuous gravitational wave signal, the challenges to finding such signals in noisy data, and the data analysis algorithms that have been developed to address those challenges. I present a quantitative analysis of 291 continuous wave searches from 78 papers, published from 2003 to 2022, and compare their sensitivities and coverage of the signal model parameter space.

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K. Wette
Mon, 15 May 23
13/53

Comments: 43 pages, 10 figures, 3 tables. Invited review for special issue of Astroparticle Physics: ‘Gravitational Waves and Multi-messenger Astrophysics’. A machine-readable version of Table A.3 is provided in the ancillary files

Probing the Origin of Primordial Black Holes through Novel Gravitational Wave Spectrum [CL]

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http://arxiv.org/abs/2305.07569


In this article we investigate the cumulative stochastic gravitational wave spectra as a tool to gain insight on the creation mechanism of primordial black holes. We consider gravitational waves from the production mechanism of primordial black holes and from the gravitational interactions of those primordial black holes among themselves and other astrophysical black holes. We specifically focus on asynchronous bubble nucleation during a first order phase transition as the creation mechanism. We have used two benchmark phase transitions through which the primordial black holes and the primary gravitational wave spectra have been generated. We have considered binary systems and close hyperbolic interactions of primordial black holes with other primordial and astrophysical black holes as the source of the secondary part of the spectra. We have shown that this unique cumulative spectra have features which directly and indirectly depend on the specifics of the production mechanism.

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I. Banerjee and U. Dey
Mon, 15 May 23
35/53

Comments: 22 pages, 9 figures, 2 tables

First-order phase transitions in Yang-Mills theories and the density of state method [CL]

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http://arxiv.org/abs/2305.07463


When studied at finite temperature, Yang-Mills theories in $3+1$ dimensions display the presence of confinement/deconfinement phase transitions, which are known to be of first order — the $SU(2)$ gauge theory being the exception. Theoretical as well as phenomenological considerations indicate that it is essential to establish a precise characterisation of these physical systems in proximity of such phase transitions. We present and test a new method to study the critical region of parameter space in non-Abelian quantum field theories on the lattice, based upon the Logarithmic Linear Relaxation (LLR) algorithm. We apply this method to the $SU(3)$ Yang Mills lattice gauge theory, and perform extensive calculations with one fixed choice of lattice size. We identify the critical temperature, and measure interesting physical quantities near the transition. Among them, we determine the free energy of the model in the critical region, exposing for the first time its multi-valued nature with a numerical calculation from first principles, providing this novel evidence in support of a first order phase transition. This study sets the stage for future high precision measurements, by demonstrating the potential of the method.

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B. Lucini, D. Mason, M. Piai, et. al.
Mon, 15 May 23
48/53

Comments: 25 pages, 21 figures

Phase Transition Phenomenology with Nonparametric Representations of the Neutron Star Equation of State [HEAP]

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http://arxiv.org/abs/2305.07411


Astrophysical observations of neutron stars probe the structure of dense nuclear matter and have the potential to reveal phase transitions at high densities. Most recent analyses are based on parametrized models of the equation of state with a finite number of parameters and occasionally include extra parameters intended to capture phase transition phenomenology. However, such models restrict the types of behavior allowed and may not match the true equation of state. We introduce a complementary approach that extracts phase transitions directly from the equation of state without relying on, and thus being restricted by, an underlying parametrization. We then constrain the presence of phase transitions in neutron stars with astrophysical data. Current pulsar mass, tidal deformability, and mass-radius measurements disfavor only the strongest of possible phase transitions (latent energy per particle $\gtrsim 100\,\mathrm{MeV}$). Weaker phase transitions are consistent with observations. We further investigate the prospects for measuring phase transitions with future gravitational-wave observations and find that catalogs of \result{$O(100)$} events will (at best) yield Bayes factors of $\sim 10:1$ in favor of phase transitions even when the true equation of state contains very strong phase transitions. Our results reinforce the idea that neutron star observations will primarily constrain trends in macroscopic properties rather than detailed microscopic behavior. Fine-tuned equation of state models will likely remain unconstrained in the near future.

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R. Essick, I. Legred, K. Chatziioannou, et. al.
Mon, 15 May 23
53/53

Comments: 18 pages (+12 pages of references and appendix), 17 figures, 5 tables

Untargeted Bayesian search of anisotropic gravitational-wave backgrounds through the analytical marginalization of the posterior [CL]

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http://arxiv.org/abs/2305.06502


We develop a method to perform an untargeted Bayesian search for anisotropic gravitational-wave backgrounds that can efficiently and accurately reconstruct the background intensity map. Our method employs an analytic marginalization of the posterior of the spherical-harmonic components of the intensity map, without assuming the background possesses any specific angular structure. The key idea is to realize that the likelihood function is a multivariable Gaussian of the spherical-harmonic components of the energy spectrum of the gravitational-wave background. If a uniform and wide prior of these spherical-harmonic components is prescribed, the marginalized posterior and the Bayes factor can be well approximated by a high-dimensional Gaussian integral. The analytical marginalization allows us to regard the spherical-harmonic components of the intensity map of the background as free parameters, and to construct their individual marginalized posterior distribution in a reasonable time, even though many spherical-harmonic components are required. The marginalized posteriors can, in turn, be used to accurately construct the intensity map of the background. By applying our method to mock data, we show that we can recover precisely the angular structures of various simulated anisotropic backgrounds, without assuming prior knowledge of the relation between the spherical-harmonic components predicted by a given model. Our method allows us to bypass the time-consuming numerical sampling of a high-dimensional posterior, leading to a more model-independent and untargeted Bayesian measurement of the angular structures of the gravitational-wave background.

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A. Chung and N. Yunes
Fri, 12 May 23
2/53

Comments: 22 pages, 6 figures

What are neutron stars made of? Gravitational waves may reveal the answer [CL]

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http://arxiv.org/abs/2305.06606


Neutron stars are one of the most mysterious wonders in the Universe. Their extreme densities hint at new and exotic physics at work within. Gravitational waves could be the key to unlocking their secrets. In particular, a first detection of gravitational waves from rapidly-spinning, deformed neutron stars could yield new insights into the physics of matter at extreme densities and under strong gravity. Once a first detection is made, a critical challenge will be to robustly extract physically interesting information from the detected signals. In this essay, we describe initial research towards answering this challenge, and thereby unleashing the full power of gravitational waves as an engine for the discovery of new physics.

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N. Lu, S. Scott and K. Wette
Fri, 12 May 23
16/53

Comments: 14 pages, 2 figures. This essay was awarded 5th Place in the Gravity Research Foundation 2023 Awards for Essays on Gravitation. To appear in International Journal of Modern Physics D

Effect of the cosmological model on LIV constraints from GRB Time-Delays datasets [CL]

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http://arxiv.org/abs/2305.06504


Putting constraints on a possible Lorentz Invariance Violation (LIV) from astrophysical sources such as gamma-ray bursts (GRBs) is an essential tool for finding evidences of new theories of quantum gravity (QG) that predict energy-dependent speed of light. Such a search has its own difficulties, so usually, the effect of the cosmological model is understudied and the default model is a fixed-parameters $\Lambda$CDM. In this work, we use different astrophysical datasets to study the effect of a number of dark energy models on the LIV constrains. To this end, we combine two public time-delay GRB datasets with the supernovae Pantheon dataset, a number of angular baryonic acoustic oscillations (BAO), the cosmic microwave background (CMB) distance prior and a GRB or quasars dataset. We find for $\alpha$ the expected average value of $\sim 4 \times 10^{-4}$, corresponding to $E_{QG}\ge 10^{17}$ GeV for both time-delay (TD) datasets, with the second one being more sensitive to the cosmological model. We find that the cosmology amounts to at least 20\% deviation in our constraints on the energy. Also interestingly, adding the TD points makes the DE models less-preferable statistically and shifts the value of the parameter $c/(H_0 r_d)$ down, making it smaller than the expected value. We see that possible LIV measurements depend critically on the transparency of the assumptions behind the published data with respect to cosmology and that taking it into account may be important contribution in the case of possible detection.

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D. Staicova
Fri, 12 May 23
26/53

Comments: 19 pages, prepared for the Classical and Quantum Gravity focus issue “Focus on Quantum Gravity Phenomenology in the Multi-Messenger Era: Challenges and Perspectives”

Constraining Primordial Magnetic Fields with Line-Intensity Mapping [CEA]

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http://arxiv.org/abs/2305.06440


Primordial magnetic fields (PMFs) offer a compelling explanation for the origin of observed magnetic fields, especially on extragalactic scales. Such PMFs give rise to excess of power in small scale matter perturbations that could strongly influence structure formation. We study the impact of the magnetically enhanced matter power spectrum on the signal that will be observed by line-intensity mapping (LIM) surveys targeting carbon monoxide (CO) emission from star-forming galaxies at high redshifts. Specifically, the voxel intensity distribution of intensity maps provides access to small-scale information, which makes it highly sensitive to signatures of PMFs on matter overdensities. We present forecasts for future LIM CO surveys, finding that they can constrain PMF amplitudes as small as $\sigma_{B,0}\sim0.04-1\,{\rm nG}$, depending on the magnetic spectral index and the targeted redshifts.

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T. Adi, S. Libanore, H. Cruz, et. al.
Fri, 12 May 23
29/53

Comments: 9 pages, 3 figures, 2 tables

Cosmological constraints on R2-AB model [CEA]

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http://arxiv.org/abs/2305.06392


Nowadays, efforts are being devoted to the study of alternative cosmological scenarios, in which, modifications of General Relativity (GR) theory have been proposed to explain the late cosmic acceleration, without assuming the existence of the dark energy (DE) component. We investigate the $R^2$-corrected Appleby-Battye model, or $R^2$-AB model, which consists of an $f(R)$ model with only one extra free parameter $b$, besides the cosmological parameters of the flat-$\Lambda$CDM model: $H_0$ and $\Omega_{m,0}$. Regarding this model, it was already shown that a positive value for $b$ is required for the model to be consistent with Solar System tests, moreover, the condition for the existence of a de~Sitter state requires $b \ge 1.6$. To impose observational constraints on the $R^2$-AB model, we consider in our analyses two data sets: cosmic chronometer $H(z)$ data for the background level, and $f\sigma_8$ data, for the perturbative level. The first one provides $b = 1.6^{+3.1}{-0.0}$ and the cosmological parameters ${H_0 ,\Omega{m,0}}$ in agreement to Planck values, while the second one, indicates $b = 1.76^{+2.91}{-0.15}$ and the parameters ${\Omega{m,0},\sigma_{8,0} }$ also in agreement to Planck values; in the last case the data was marginalized over the parameter $H_0$. Additionally, we perform illustrative analyses that compare this $f(R)$ model with the flat-$\Lambda$CDM model, considering several values of the parameter $b$, for diverse cosmological functions like the Hubble function $H(z)$, the equation of state $w_{eff}(z)$, the parametrized growth rate of cosmic structures $f \sigma_8$, and $\sigma_8(z)$. The overall conclusion is that the $R^2$-AB model is a promising $f(R)$ model that deserves to continue being tested with diverse cosmological data.

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B. Ribeiro, A. Bernui and M. Campista
Fri, 12 May 23
32/53

Comments: N/A

Constraining gravitational wave amplitude birefringence with GWTC-3 [CL]

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http://arxiv.org/abs/2305.05844


The propagation of gravitational waves can reveal fundamental features of the structure of space-time. For instance, differences in the propagation of gravitational-wave polarizations would be a smoking gun for parity violations in the gravitational sector, as expected from birefringent theories like Chern-Simons gravity. Here we look for evidence of amplitude birefringence in the latest LIGO-Virgo catalog (GWTC-3) through the use of birefringent templates inspired by dynamical Chern-Simons gravity. From 71 binary-black-hole signals, we obtain the most precise constraints on gravitational-wave amplitude birefringence yet, measuring a birefringent attenuation of $\kappa = – 0.019^{+0.038}{-0.029}\, \mathrm{Gpc}^{-1}$ at 100 Hz with 90% credibility, equivalent to a parity-violation energy scale of $M{PV} \gtrsim 6.8\times 10^{-21}\, \mathrm{GeV}$.

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T. Ng, M. Isi, K. Wong, et. al.
Thu, 11 May 23
3/55

Comments: N/A

Implications of pulsar timing array observations for LISA detections of massive black hole binaries [HEAP]

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http://arxiv.org/abs/2305.05955


Pulsar timing arrays (PTAs) and the Laser Interferometer Space Antenna (LISA) will open complementary observational windows on massive black-hole binaries (MBHBs), i.e., with masses in the range $\sim 10^6 – 10^{10}\,$ M${\odot}$. While PTAs may detect a stochastic gravitational-wave background from a population of MBHBs, during operation LISA will detect individual merging MBHBs. To demonstrate the profound interplay between LISA and PTAs, we estimate the number of MBHB mergers that one can expect to observe with LISA by extrapolating direct observational constraints on the MBHB merger rate inferred from PTA data. For this, we postulate that the common noise currently detected in PTAs is an astrophysical background sourced by a single MBHB population. We then constrain the LISA detection rate, $\mathcal{R}$, in the mass-redshift space by combining our Bayesian-inferred merger rate with LISA’s sensitivity to spin-aligned, inspiral-merger-ringdown waveforms. Using an astrophysically-informed formation model, we predict a 95$\%$ upper limit on the detection rate of $\mathcal{R} < 134\,{\rm yr}^{-1}$ for binaries with total masses in the range $10^7 – 10^8\,$ M${\odot}$. For higher masses, i.e., $>10^8\,$ M$_{\odot}$, we find $\mathcal{R} < 2\,(1)\,\mathrm{yr}^{-1}$ using an astrophysically-informed (agnostic) formation model, rising to $11\,(6)\,\mathrm{yr}^{-1}$ if the LISA sensitivity bandwidth extends down to $10^{-5}$ Hz. Forecasts of LISA science potential with PTA background measurements should improve as PTAs continue their search.

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N. Steinle, H. Middleton, C. Moore, et. al.
Thu, 11 May 23
10/55

Comments: N/A

Scale invariant curvature perturbations from a spontaneously decaying scalar field [CEA]

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http://arxiv.org/abs/2305.06320


The evolution of superhorizon curvature perturbations in a two-component interacting universe is considered. It is found that adiabatic modes conserve the total curvature perturbation $\zeta$, unless there are stages in which the rate of dissipation of one component into another is not constant. Moreover, our result shows that when the rate is varying it is possible for ‘isocurvature’ perturbations generated during reheating to alter the amplitude of an adiabatic curvature mode even when the mode is outside the horizon. Specifically, if an indefinitely large rate $\Gamma$ for massive particles decaying into photons develops rapidly amid vanishingly small initial values (before decay) of the total curvature $\zeta_i$ and Newtonian potential $\Phi_i$, such that the product $\Gamma\zeta_i$ and $\Gamma\Phi_i$ become a pair of finite and universal constants for all superhorizon scales afterwards, Harrison-Zel’dovich scale-invariant power spectrum could be synthesized from a homogeneous state without inflation at all.

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R. Lieu and C. Shi
Thu, 11 May 23
18/55

Comments: CQG in press

A robust explanation of CMB anomalies with a new formulation of inflationary quantum fluctuations [CL]

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http://arxiv.org/abs/2305.06057


The presence of CMB Hemispherical Asymmetry (HPA) challenges the current understanding of inflationary cosmology which does not generically predict the parity violation in the primordial correlations. In this paper, we shall review the recently proposed resolution to this based on a new formulation of quantizing inflationary fluctuations by focusing on the discrete spacetime transformations in a gravitational context. The predictive power of this formulation is that one can generate a scale dependent HPA in the context of single field inflation for all the primordial modes including scalar and tensor fluctuations without introducing any additional parameters. This result can be seen as an indication of spontaneous breaking of $\mathcal{C}\mathcal{P}\mathcal{T}$ symmetry in an expanding Universe, if confirmed by future observations it would be a great leap in the subject of quantum field theory in curved spacetime.

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K. Kumar and J. Marto
Thu, 11 May 23
23/55

Comments: 13 pages, 2 figures, Based on the talk given at the workshop on “Tensions in Cosmology” in Corfu 2022. This manuscript is written for Proceedings of Science (PoS), Corfu 2022 and it is based on arXiv: 2209.03928 [gr-qc]

Exploring the spectrum of stochastic gravitational-wave anisotropies with pulsar timing arrays [CEA]

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http://arxiv.org/abs/2305.05690


Anisotropies in the nanohertz gravitational-wave background are a compelling next target for pulsar timing arrays (PTAs). Measurements or informative upper limits to the anisotropies are expected in the near future and can offer important clues about the origin of the background and the properties of the sources. Given that each source is expected (in the simplest scenario of circular inspirals) to emit at a fixed frequency, the anisotropy will most generally vary from one frequency to another. The main result presented in this work is an analytical model for the anisotropies produced by a population of inspiralling supermassive black-hole binaries (SMBHBs). This model can be immediately connected with parametrizations of the SMBHB mass function and can be easily expanded to account for new physical processes taking place within the PTA frequency band. We show that a variety of SMBHB models predict significant levels of anistropy at the highest frequencies accessible to PTA observations and that measurements of anisotropies can offer new information regarding this population beyond the isotropic component. We also model the impact of additional dynamical effects driving the binary towards merger and show that, if these processes are relevant within the PTA band, the detectability of anisotropies relative to the isotropic background will be enhanced. Finally, we use the formalism presented in this work to predict the level anisotropy of the circular and linear polarizations of the SGWB due to the distribution of binary orientation angles with respect to the line of sight.

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G. Sato-Polito and M. Kamionkowski
Thu, 11 May 23
25/55

Comments: 10 pages, 4 figures

Extreme-mass-ratio inspirals into rotating boson stars: nonintegrability, chaos, and transient resonances [CL]

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http://arxiv.org/abs/2305.05691


General relativity predicts that black holes are described by the Kerr metric, which has integrable geodesics. This property is crucial to produce accurate waveforms from extreme-mass-ratio inspirals. Astrophysical environments, modifications of gravity and new fundamental fields may lead to nonintegrable geodesics, inducing chaotic effects. We study geodesics around self-interacting rotating boson stars and find robust evidence of nonintegrability and chaos. We identify islands of stability around resonant orbits, where the orbital radial and polar oscillation frequency ratios, known as rotation numbers, remain constant throughout the island. These islands are generically present both in the exterior and the interior of compact boson stars. A monotonicity change of rotation curves takes place as orbits travel from the exterior to the interior of the star. Therefore, configurations with neutron-star-like compactness can support degenerate resonant islands. This anomaly is reported here for the first time and it is not present in black holes. Such configurations can also support extremely prolonged resonant islands that span from the exterior to the interior of the star and are shielded by thick chaotic layers. We adiabatically evolve inspirals using approximated post-Newtonian fluxes and find time-dependent plateaus in the rotation curves which are associated with island-crossing orbits. Crossings of external islands give rise to typical gravitational-wave glitches found in non-Kerr objects. Furthermore, when an inspiral is traversing an internal island that is surrounded by a thick chaotic layer, a new type of simultaneous multifrequency glitch occurs that may be detectable with space interferometers such as LISA, and can serve as evidence of an extreme-mass-ratio inspiral around a supermassive boson star.

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K. Destounis, F. Angeloni, M. Vaglio, et. al.
Thu, 11 May 23
28/55

Comments: 22 pages, 17 figures, higher resolution plots available upon request

On the degeneracies between baryons, massive neutrinos and f(R) gravity in Stage IV cosmic shear analyses [CEA]

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http://arxiv.org/abs/2305.06350


Modelling nonlinear structure formation is essential for current and forthcoming cosmic shear experiments. We combine the halo model reaction formalism, implemented in the REACT code, with the COSMOPOWER machine learning emulation platform, to develop and publicly release REACTEMU-FR, a fast and accurate nonlinear matter power spectrum emulator for $f(R)$ gravity with massive neutrinos. Coupled with the state-of-the-art baryon feedback emulator BCEMU, we use REACTEMU-FR to produce Markov Chain Monte Carlo forecasts for a cosmic shear experiment with typical Stage IV specifications. We find that the inclusion of highly nonlinear scales (multipoles between $1500\leq \ell \leq 5000$) only mildly improves constraints on most standard cosmological parameters (less than a factor of 2). In particular, the necessary modelling of baryonic physics effectively damps most constraining power on the sum of the neutrino masses and modified gravity at $\ell \gtrsim 1500$. Using an approximate baryonic physics model produces mildly improved constraints on cosmological parameters which remain unbiased at the $1\sigma$-level, but significantly biases constraints on baryonic parameters at the $> 2\sigma$-level.

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A. Mancini and B. Bose
Thu, 11 May 23
32/55

Comments: 16 pages, 10 figures, REACTEMU-FR available at this https URL

Starobinsky Inflation from String Theory? [CL]

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http://arxiv.org/abs/2305.05703


Starobinsky inflation is currently one of the best models concerning agreement with cosmological data. Despite this observational success, it is still lacking a robust embedding into a UV complete theory. Previous efforts to derive Starobinsky inflation from string theory have been based on the derivation of higher derivative curvature terms from the low-energy limit of ten-dimensional string theory. This approach is however known to fail due to the difficulty to tame the effect of contributions proportional to the Ricci scalar to a power larger than two. In this paper we investigate an alternative attempt which exploits instead the ubiquitous presence of scalar fields in string compactifications combined with the fact that Starobinsky inflation can be recast as Einstein gravity coupled to a scalar field with a precise potential and conformal coupling to matter fermions. We focus in particular on type IIB K\”ahler moduli since they have shown to lead to exponential potentials with a Starobinsky-like plateau. We consider three classes of moduli with a different topological origin: the volume modulus, bulk fibre moduli, and blow-up modes. The only modulus with the correct coupling to matter is the volume mode but its potential does not feature any plateau at large field values. Fibre moduli admit instead a potential very similar to Starobinsky inflation with a natural suppression of higher curvature corrections, but they cannot reproduce the correct conformal coupling to matter. Blow-up modes have both a wrong potential and a wrong coupling. Our analysis implies therefore that embedding Starobinsky inflation into string theory seems rather hard. Finally, it provides a detailed derivation of the coupling to matter of fibre moduli which could be used as a way to discriminate Starobinsky from fibre inflation.

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M. Brinkmann, M. Cicoli and P. Zito
Thu, 11 May 23
38/55

Comments: 24 pages, 4 figures

Improved ranking statistics of the GstLAL inspiral search for compact binary coalescences [IMA]

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http://arxiv.org/abs/2305.06286


Starting from May 2023, the LIGO Scientific, Virgo and KAGRA Collaboration is planning to conduct the fourth observing run with improved detector sensitivities and an expanded detector network including KAGRA. Accordingly, it is vital to optimize the detection algorithm of low-latency search pipelines, increasing their sensitivities to gravitational waves from compact binary coalescences. In this work, we discuss several new features developed for ranking statistics of GstLAL-based inspiral pipeline, which mainly consist of: the signal contamination removal, the bank-$\xi^2$ incorporation, the upgraded $\rho-\xi^2$ signal model and the integration of KAGRA. An injection study demonstrates that these new features improve the pipeline’s sensitivity by approximately 15% to 20%, paving the way to further multi-messenger observations during the upcoming observing run.

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L. Tsukada, P. Joshi, S. Adhicary, et. al.
Thu, 11 May 23
42/55

Comments: 13pages, 6figures

Gravitational Wave Peeps from EMRIs and their Implication for LISA Signal Confusion Noise [CL]

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http://arxiv.org/abs/2305.05793


Scattering events around a supermassive black hole will occasionally toss a stellar-mass compact object into an orbit around the supermassive black hole, beginning an extreme mass ratio inspiral. The early stages of such a highly eccentric orbit will not produce detectable gravitational waves as the source will only be in a suitable frequency band briefly when it is close to periapsis during each long-period orbit. This burst of emission, firmly in the millihertz band is the gravitational wave peep. While a single peep is not likely to be detectable, if we consider an ensemble of such subthreshold sources, spread across the universe, together they produce an unresolvable background noise that may obscure sources otherwise detectable by the Laser Interferometer Space Antenna, the proposed space-based gravitational wave detector. Previous studies of the extreme mass ratio burst signal confusion background focused more on parabolic orbits going very near the supermassive black hole and on events near the galactic center. We seek to improve this characterization by implementing numerical kludge waveforms that can calculate highly eccentric orbits with relativistic effects focusing on orbits which are farther away from the supermassive black hole and thus less likely to be detectable on their own, but will otherwise contribute to the background signal confusion noise. Here we present the waveforms and spectra of the gravitational wave peeps generated from recent calculations of extreme mass ratio inspirals/bursts capture parameters and discuss how these can be used to estimate the signal confusion noise generated by such events.

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D. Oliver, A. Johnson, J. Berrier, et. al.
Thu, 11 May 23
46/55

Comments: 10 pages, 7 figures

QLUSTER: quick clusters of merging binary black holes [HEAP]

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http://arxiv.org/abs/2305.04987


This short document illustrates QLUSTER: a toy model for populations of binary black holes in dense astrophysical environments. QLUSTER is a simple tool to investigate the occurrence and properties of hierarchical black-hole mergers detectable by gravitational-wave interferometers. QLUSTER is not meant to rival the complexity of state-of-the-art population synthesis and N-body codes but rather provide a fast, approximate, and easy-to-interpret framework to investigate some of the key ingredients of the problem. These include the binary pairing probability, the escape speed of the host environment, and the merger generation. We also introduce the “hierarchical-merger efficiency” — an estimator that quantifies the relevance of hierarchical black-hole mergers in a given astrophysical environment.

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D. Gerosa and M. Mould
Wed, 10 May 23
2/65

Comments: Contribution to the 2023 Gravitation session of the 57th Rencontres de Moriond

Reconstructing k-inflation from $n_s(N)$ and reheating constraints [CL]

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http://arxiv.org/abs/2305.05042


Inspired by the reconstruction scheme of the inflaton field potential $V(\phi)$ from the attractors$n_s(N)$, we investigate the viability of reconstruct the inflationary potential within the framework of k-inflation for a non-linear kinetic term $K(X)=k_{n+1}X^n$ through three expressions for the scalar spectral index $n_s(N)$, namely: (i) $n_s-1=-\frac{2}{N}$, (ii) $n_s-1=-\frac{p}{N}$, and (iii) $n_s-1=-\frac{\beta}{N^q}$. For each reconstructed potential, we determine the values of the parameter space which characterize it by requiring that it must reproduce the observable parameters from PLANCK 2018 and BICEP/Keck results. Furthermore, we analyze the reheating era by assuming a constant equation of state, in which we derive the relations between the reheating duration, the temperature at the end of reheating together with the reheating epoch, and the number of $e$-folds during inflation. In this sense, we unify the inflationary observables in order to narrow the parameter space of each model within the framework of the reconstruction in k-inflation.

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R. Herrera, M. Housset, C. Osses, et. al.
Wed, 10 May 23
3/65

Comments: 40 pages and 6 figures

Calculating the Gravitational Waves Emitted from High-speed Sources [CL]

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http://arxiv.org/abs/2305.04969


The possibility of forming gravitational-wave sources with high center-of-mass (c.m.) velocities in the vicinity of supermassive black holes requires us to develop a method of deriving the waveform in the observer’s frame. Here we show that in the limit where the c.m. velocity is high but the relative velocities of the components of the source are small, we can solve the problem by directly integrating the relaxed Einstein field equation. In particular, we expand the result into multipole components which can be conveniently calculated given the orbit of the source in the observer’s frame. Our numerical calculations using arbitrary c.m. velocities show that the result is consistent with the Lorentz transformation of GWs to the leading order of the radiation field. Moreover, we show an example of using this method to calculate the waveform of a scattering event between the high-speed ($\sim 0.1c$) stellar objects embedded in the accretion disk of an active galactic nucleus. Our multipole-expansion method not only has advantages in analyzing the results from stellar-dynamical models but also provides new insight into the multipole properties of the GWs emitted from a high-speed source.

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H. Yan, X. Chen and A. Torres-Orjuela
Wed, 10 May 23
7/65

Comments: 9 pages, 2 figures. Accepted by PRD

Instability of scalarized compact objects in Einstein-scalar-Gauss-Bonnet theories [CL]

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http://arxiv.org/abs/2305.05185


We investigate the linear stability of scalarized black holes (BHs) and neutron stars (NSs) in the Einstein-scalar-Gauss-Bonnet (GB) theories against the odd- and even-parity perturbations including the higher multipole modes. We show that the angular propagation speeds in the even-parity perturbations in the $\ell \to \infty$ limit, with $\ell$ being the angular multipole moments, become imaginary and hence scalarized BH solutions suffer from the gradient instability. We show that such an instability appears irrespective of the structure of the higher-order terms in the GB coupling function and is caused purely due to the existence of the leading quadratic term and the boundary condition that the value of the scalar field vanishes at the spatial infinity.~This indicates that the gradient instability appears at the point in the mass-charge diagram where the scalarized branches bifurcate from the Schwarzschild branch. We also show that scalarized BH solutions realized in a nonlinear scalarization model also suffer from the gradient instability in the even-parity perturbations. Our result also suggests the gradient instability of the exterior solutions of the static and spherically-symmetric scalarized NS solutions induced by the same GB coupling functions.

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M. Minamitsuji and S. Mukohyama
Wed, 10 May 23
31/65

Comments: 14 pages

R-modes as a New Probe of Dark Matter in Neutron Stars [HEAP]

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http://arxiv.org/abs/2305.05664


In this work, we perform the first systematic investigation of effects of the presence of dark matter on r-mode oscillations in neutron stars (NSs). Using a self-interacting dark matter (DM) model based on the neutron decay anomaly and a hadronic model obtained from the posterior distribution of a recent Bayesian analysis, we impose constraints on the DM self-interaction strength using recent multimessenger astrophysical observations. The constrained DM interaction strength is then used to estimate DM self-interaction cross section and shear viscosity resulting from DM, which is found to be several orders of magnitude smaller than shear viscosity due to hadronic matter. Assuming that the DM fermion is in chemical equilibrium with the neutrons in the neutron star, we estimate the bulk viscosity resulting from the dark decay of neutrons, and find it to be much smaller than the hadronic bulk viscosity. We also conclude that the instability window with minimal hadronic damping mechanisms can become smaller when including DM shear and bulk viscosity but remains incompatible with the X-ray and pulsar observational data for the chosen DM model.

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S. Shirke, S. Ghosh, D. Chatterjee, et. al.
Wed, 10 May 23
34/65

Comments: 29 pages, 12 figures, 1 table. To be submitted to JCAP. Comments are welcome

Multi-messenger observations of double neutron stars in Galactic disk with gravitational and radio waves [HEAP]

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http://arxiv.org/abs/2305.05202


We evaluate the prospects for radio follow-up of the double neutron stars (DNSs) in the Galactic disk that could be detected through future space-borne gravitational wave (GW) detectors. We first simulate the DNS population in the Galactic disk that is accessible to space-borne GW detectors according to the merger rate from recent LIGO results. Using the inspiraling waveform for the eccentric binary, the average number of the DNSs detectable by TianQin (TQ), LISA, and TQ+LISA are 217, 368, and 429, respectively. For the joint GW detection of TQ+LISA, the forecasted parameter estimation accuracies, based on the Fisher information matrix, for the detectable sources can reach the levels of $\Delta P_{\mathrm b}/P_{\mathrm b} \lesssim 10^{-6}$, $\Delta \Omega \lesssim 100~{\mathrm {deg}}^2$, $\Delta e/e \lesssim 0.3$, and $\Delta \dot{P}{\mathrm b} / \dot{P}{\mathrm b} \lesssim 0.02$. These estimation accuracies are fitted in the form of power-law function of signal-to-noise ratio. Next, we simulate the radio pulse emission from the possible pulsars in these DNSs according to pulsar beam geometry and the empirical distributions of spin period and luminosity. For the DNSs detectable by TQ+LISA, the average number of DNSs detectable by the follow-up pulsar searches using the Parkes, FAST, SKA1, and SKA are 8, 10, 43, and 87, respectively. Depending on the radio telescope, the average distances of these GW-detectable pulsar binaries vary from 1 to 7 kpc. Considering the dominant radiometer noise and phase jitter noise, the timing accuracy of these GW-detectable pulsars can be as low as 70 ${\rm ns}$ while the most probable value is about 100 $\mu {\rm s}$.

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W. Feng, J. Chen, Y. Wang, et. al.
Wed, 10 May 23
41/65

Comments: 15 pages, 9 figures, 3 tables. To be published in PRD

Performance of the low-latency GstLAL inspiral search towards LIGO, Virgo, and KAGRA's fourth observing run [CL]

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http://arxiv.org/abs/2305.05625


GstLAL is a stream-based matched-filtering search pipeline aiming at the prompt discovery of gravitational waves from compact binary coalescences such as the mergers of black holes and neutron stars. Over the past three observation runs by the LIGO, Virgo, and KAGRA (LVK) collaboration, the GstLAL search pipeline has participated in several tens of gravitational wave discoveries. The fourth observing run (O4) is set to begin in May 2023 and is expected to see the discovery of many new and interesting gravitational wave signals which will inform our understanding of astrophysics and cosmology. We describe the current configuration of the GstLAL low-latency search and show its readiness for the upcoming observation run by presenting its performance on a mock data challenge. The mock data challenge includes 40 days of LIGO Hanford, LIGO Livingston, and Virgo strain data along with an injection campaign in order to fully characterize the performance of the search. We find an improved performance in terms of detection rate and significance estimation as compared to that observed in the O3 online analysis. The improvements are attributed to several incremental advances in the likelihood ratio ranking statistic computation and the method of background estimation.

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B. Ewing, R. Huxford, D. Singh, et. al.
Wed, 10 May 23
50/65

Comments: 16 pages, 17 figures

New MGCAMB tests of gravity with CosmoMC and Cobaya [CEA]

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http://arxiv.org/abs/2305.05667


We present a new version of MGCAMB, a patch for the Einstein-Boltzmann solver CAMB for cosmological tests of gravity. New features include a new cubic-spline parameterization allowing for a simultaneous reconstruction of $\mu$, $\Sigma$ and the dark energy density fraction $\Omega_X$ as functions of redshift, the option to work with a direct implementation of $\mu$, $\Sigma$ (instead of converting to $\mu$, $\gamma$ first), along with the option to test models with a scalar field coupled only to dark matter, and the option to include dark energy perturbations when working with $w\ne -1$ backgrounds, to restore consistency with CAMB in the GR limit. This version of MGCAMB comes with a python wrapper to run it directly from the python interface, an implementation in the latest version of CosmoMC, and can be used with Cobaya.

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Z. Wang, S. Mirpoorian, L. Pogosian, et. al.
Wed, 10 May 23
57/65

Comments: 8 pages + 2 appendices, 4 figures; MGCAMB, MGCosmoMC and MGCobaya available at this https URL, this https URL, this https URL

Exploring departures from Schwarzschild black hole geometry in $f(R)$ gravity [CL]

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http://arxiv.org/abs/2305.04695


Different astrophysical methods can be combined to detect possible deviations from General Relativity. In this work, we consider a class of $f(R)$ gravity models selected by the existence of Noether symmetries. In this framework, it is possible to determine a set of static and spherically symmetric black hole solutions, encompassing small departures from the Schwarzschild geometry. In particular, when gravity is the only dominating interaction, we exploit the ray-tracing technique to reconstruct the image of a black hole, the epicyclic frequencies, and the black hole shadow profile. Moreover, when matter dynamics is also affected by an electromagnetic radiation force, we take into account the general relativistic Poynting-Robertson effect. In light of the obtained results, the proposed strategy results to be robust and efficient: on the one hand, it allows to investigate gravity from strong to weak field regimes; on the other hand, it is capable of detecting small departures from General Relativity, depending on the current observational sensitivity.

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V. Falco, F. Bajardi, R. D’Agostino, et. al.
Tue, 9 May 23
1/88

Comments: 19 pages; 7 figures; 2 tables; accepted for publication on EPJ C

Memory matters : Gravitational wave memory of compact binary coalescence in the presence of matter effects [CL]

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http://arxiv.org/abs/2305.04761


Binary neutron stars (BNS) and neutron star-black hole (NSBH) binaries are one of the most promising gravitational wave (GW) sources to probe matter effects. Upcoming observing runs of LIGO-Virgo-KAGRA detectors and future third generation detectors like Einstein Telescope and Cosmic Explorer will allow the extraction of detailed information on these matter effects from the GW signature of BNS and NSBH systems. One subtle effect which may be helpful to extract more information from the detection of compact binary systems is the non-linear memory. In this work, we investigate the observational consequences of gravitational wave non-linear memory in the presence of matter effects.
We start by quantifying the impact of non-linear memory on distinguishing BNS mergers from binary black holes (BBH) or NSBH mergers. We find that for the third generation detectors, the addition of non-linear memory to the GW signal model expands the parameter space where BNS signals become distinguishable from the BBH and NSBH signals. Using numerical relativity simulations, we also study the non-linear memory generated from the post-merger phase of BNS systems. We find that it does not show a strong dependence on the equation of state of the NS. However, the non-linear memory from the BNS post-merger phase is much lower than the one from BBH systems of the same masses. Furthermore, we compute the detection prospects of non-linear memory from the post-merger phase of NS systems by accumulating signal strength from a population of BNS mergers for the current and future detectors. Finally, we discuss the impact of possible linear memory from the dynamical ejecta of BNS and NSBH systems and its signal strength relative to the non-linear memory. We find that linear memory almost always has a much weaker effect than non-linear memory.

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D. Lopez, S. Tiwari and M. Ebersold
Tue, 9 May 23
4/88

Comments: N/A

Exploring the nature of black hole and gravity with an imminent merging binary of supermassive black holes [CL]

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http://arxiv.org/abs/2305.04478


A supermassive binary black-hole candidate SDSS J1430+2303 reported recently motivates us to investigate an imminent binary of supermassive black holes as potential gravitational wave source, the radiated gravitational waves at the end of the merger are shown to be in the band of space-borne detectors. We provide a general analysis on the required detecting sensitivity needed for probing such type gravitational wave sources and make a full discussion by considering two typically designed configurations of space-borne antennas. If a source is so close, it is possible to be detected with Taiji pathfinder-plus which is proposed to be an extension for the planned Taiji pathfinder by just adding an additional satellite to the initial two satellites. The gravitational wave detection on such kind of source enables us to explore the properties of supermassive black holes and the nature of gravity.

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X. Zhong, W. Han, Z. Luo, et. al.
Tue, 9 May 23
6/88

Comments: N/A

Investigating Loop Quantum Gravity Through Strong Gravitational Lensing Effects by Rotating Black Hole and EHT Observations [CL]

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http://arxiv.org/abs/2305.04336


We investigate gravitational lensing in the strong deflection regime by loop quantum gravity (LQG)-motivated rotating black hole (LMRBH) metrics with an additional parameter $l$ besides mass $M$ and rotation $a$. The LMRBH spacetimes are regular everywhere, asymptotically encompassing the Kerr black hole as a particular case and, depending on the parameters, describe black holes with one horizon only (BH-I), black holes with an event horizon and a Cauchy horizon (BH-II), black holes with three horizons (BH-III), or black holes with no horizons (NH) spacetime. It turns out that as the LQG parameter $l$ increases, the unstable photon orbit radius $x_{ps}$, the critical impact parameter $u_{ps}$, the deflection angle $\alpha_D(\theta)$ and angular position $\theta_{\infty}$ also increases. Meanwhile, the angular separation $s$ decreases, and relative magnitude $r_{mag}$ increases with increasing $l$ for prograde motion but they show opposite behaviour for the retrograde motion. For Sgr A*, the angular position $\theta_{\infty}$ is $\in$ (16.404, 39.8044) $\mu$as, while for M87* $\in$ (12.3246, 29.9057) $\mu$as. The angular separation $s$ is ranging $\in$ (0.008306-0.37573) $\mu$as for Sgr A* and $\in$ (0.00624-0.282295) $\mu$as for M87*. The relative magnitude $r_{mag}$ $\in$ (0.04724, 1.53831). We estimate the time delay between the first and second relativistic images using twenty supermassive galactic centre black holes as lenses. Our analysis concludes that, within the $1 \sigma$ region, a significant portion of the BH-I and BH-II and for a small portion of BH-III parameter space agrees with the EHT results of M87* and Sgr A* whereas NH is completely ruled out. We discover that the EHT results of Sgr A* place more stringent limits on the parameter space of LMRBH black holes than those established by the EHT results of M87*.

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J. Kumar, S. Islam and S. Ghosh
Tue, 9 May 23
16/88

Comments: 15 pages, 10 figures, 3 tables

Horizon fluxes of binary black holes in eccentric orbits [CL]

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http://arxiv.org/abs/2305.03771


I compute the rate of change of mass and angular momentum of a black hole, namely tidal heating, in an eccentric orbit. The change is caused due to the tidal field of the orbiting companion. I compute the result for both the spinning and non-spinning black holes in the leading order of the mean motion, namely $\xi$. I demonstrate that the rates get enhanced significantly for nonzero eccentricity. Since eccentricity in a binary evolves with time I also express the results in terms of an initial eccentricity and azimuthal frequency $\xi_{\phi}$. In the process, I developed a prescription that can be used to compute all physical quantities in a series expansion of initial eccentricity, $e_0$. This result was only known in the leading order while ignoring the contribution of the spin on the eccentricity evolution. Although the eccentricity evolution result still ignores the spin effect in the current work, the prescription can be used to compute higher-order corrections of initial eccentricity post-leading order. Using this result I computed the rate of change of mass and angular momentum of a black hole in terms of initial eccentricity and azimuthal frequency up to $\mathcal{O}(e_0^2)$.

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S. Datta
Tue, 9 May 23
21/88

Comments: N/A

On networks of space-based gravitational-wave detectors [CL]

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http://arxiv.org/abs/2305.04551


The space-based laser interferometers, LISA, Taiji and TianQin, are targeting to observe milliHz gravitational waves (GWs) in the 2030s. The joint observations from multiple space-based detectors yield significant advantages. In this work, we recap the studies and investigations for the joint space-based GW detector networks to highlight: 1) the high precision of sky localization for the massive binary black hole (BBH) coalescences and the GW sirens in the cosmological implication, 2) the effectiveness to test the parity violation in the stochastic GW background observations, 3) the efficiency of subtracting galactic foreground, 4) the improvement in stellar-mass BBH observations. We inspect alternative networks by trading off massive BBH observations and stochastic GW background observation.

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R. Cai, Z. Guo, B. Hu, et. al.
Tue, 9 May 23
26/88

Comments: 32 pages, 14 figures, reviews on recent studies about space-borne GW networks, comments and feedbacks are welcome

Breakdown of the Newton-Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars [GA]

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http://arxiv.org/abs/2305.04613


A gravitational anomaly is found at weak gravitational acceleration $g_{\rm{N}} < 10^{-9}$ m s$^{-2}$ from analyses of the dynamics of wide binary stars selected from the Gaia EDR3 database that have accurate distances, proper motions, and reliably inferred stellar masses. Implicit high-order multiplicities are required and the multiplicity fraction is calibrated so that binary internal motions agree statistically with Newtonian dynamics at a high enough acceleration of $10^{-8}$ m s$^{-2}$. The observed sky-projected motions and separation are deprojected to the three-dimensional relative velocity $v$ and separation $r$ through a Monte Carlo method, and a statistical relation between the Newtonian acceleration $g_{\rm{N}} \equiv GM/r^2$ (where $M$ is the total mass of the binary system) and a kinematic acceleration $g \equiv v^2/r$ is compared with the corresponding relation predicted by Newtonian dynamics. The empirical acceleration relation at $< 10^{-9}$ m s$^{-2}$ systematically deviates from the Newtonian expectation. A gravitational anomaly parameter $\delta_{\rm{obs-newt}}$ between the observed acceleration at $g_{\rm{N}}$ and the Newtonian prediction is measured to be: $\delta_{\rm{obs-newt}}= 0.034\pm 0.007$ and $0.109\pm 0.013$ at $g_{\rm{N}}\approx10^{-8.91}$ and $10^{-10.15}$ m s$^{-2}$, from the main sample of 26,615 wide binaries within 200 pc. These two deviations in the same direction represent a $10\sigma$ significance. The deviation represents a direct evidence for the breakdown of standard gravity at weak acceleration. At $g_{\rm{N}}=10^{-10.15}$ m s$^{-2}$, the observed to Newton predicted acceleration ratio is $g_{\rm{obs}}/g_{\rm{pred}}=10^{\sqrt{2}\delta_{\rm{obs-newt}}}=1.43\pm 0.06$. This systematic deviation agrees with the boost factor that the AQUAL theory predicts for kinematic accelerations in circular orbits under the Galactic external field.

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K. Chae
Tue, 9 May 23
38/88

Comments: 31 pages, 28 figures, submitted to ApJ

Toward robust detections of nanohertz gravitational waves [IMA]

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http://arxiv.org/abs/2305.04464


The recent observation of a common red-noise process in pulsar timing arrays (PTAs) suggests that the detection of nanohertz gravitational waves might be around the corner. However, in order to confidently attribute this red process to gravitational waves, one must observe the Hellings-Downs curve — the telltale angular correlation function associated with a gravitational-wave background. This effort is complicated by the complex modelling of pulsar noise. Without proper care, mis-specified noise models can lead to false-positive detections. Background estimation using bootstrap methods such as sky scrambles and phase shifts, which use the data to characterize the noise, are therefore important tools for assessing significance. We investigate the ability of current PTA experiments to estimate their background with “quasi-independent” scrambles — characterized by a statistical “match” below the fiducial value: $|M|<0.1$. We show that sky scrambling is affected by “saturation” after ${\cal O}(10)$ quasi-independent realizations; subsequent scrambles are no longer quasi-independent. We show phase scrambling saturates after ${\cal O}(100)$ quasi-independent realizations. With so few independent scrambles, it is difficult to make reliable statements about the $\gtrsim 5 \sigma$ tail of the null distribution of the detection statistic. We discuss various methods by which one may increase the number of independent scrambles. We also consider an alternative approach wherein one re-frames the background estimation problem so that the significance is calculated using statistically \textit{dependent} scrambles. The resulting $p$-value is in principle well-defined but may be susceptible to failure if assumptions about the data are incorrect.

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V. Marco, A. Zic, M. Miles, et. al.
Tue, 9 May 23
59/88

Comments: N/A

Exploring the viability of pseudo Nambu-Goldstone boson as ultralight dark matter in a mass range relevant for strong gravity applications [CL]

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http://arxiv.org/abs/2305.03776


We study a simple extension of the Standard Model featuring a dark sector with an ultralight pseudo Nambu-Goldstone boson as dark matter candidate. We focus on the mass range $\mathcal{O}(10^{-20} – 10^{-10})$ eV, relevant for strong gravity applications, and explore its production and evolution in the early Universe. The model is formulated in such a way that dark matter does not couple directly to photons or other Standard Model particles avoiding some of the most stringent cosmological bounds related to axion-like particles. In this work, two different scenarios are considered depending on whether dark matter is produced in a pre-inflationary or post-inflationary regime. We also discuss the effect from emergent topological defects such as cosmic strings and domain walls, and estimate the spectrum of stochastic gravitational waves produced by their decay, enabling to test the model at current and future gravitational-wave experiments.

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A. Morais, V. Oliveira, A. Onofre, et. al.
Tue, 9 May 23
72/88

Comments: 22 pages, 5 figures

Cosmic rays from heavy particle decays [CL]

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http://arxiv.org/abs/2305.03313


Multidimensional modification of gravity with a smaller mass scale of the gravitational interaction is considered. Stable by assumption dark matter particles could decay via interactions with virtual black holes. The decay rates of such processes are estimated. It is shown that with the proper fixation of the parameters the decays of these ultra-massive particles can give noticeable contribution to the flux of high energy cosmic rays in particular, near the Greisen-Zatsepin-Kuzmin limit. Such particles can also create neutrinos of very high energies observed in the existing huge underwater or ice-cube detectors.

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E. Arbuzova, A. Dolgov and A. Nikitenko
Mon, 8 May 23
12/63

Comments: 7 pages, 3 figures

One loop to rule them all: Perturbativity in the presence of ultra slow-roll dynamics [CEA]

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http://arxiv.org/abs/2305.03491


We discuss the issue of perturbativity in single-field inflationary models with a phase of ultra slow-roll (USR) tailor suited to generate an order-one abundance of primordial black holes (PBHs). More in detail, we impose the condition that loop corrections made up of short-wavelength modes enhanced by the USR dynamics do not alter the tree-level power spectrum of curvature perturbations. In our analysis, the USR phase is preceded and followed by two stages of ordinary slow-roll (SR), and we model the resulting SR/USR/SR dynamics using both instantaneous and smooth transitions. Focusing on scales relevant for CMB observations, we find that it is not possible, with these arguments, to rule out the scenario of PBH formation via USR, not even in the limit of instantaneous transition. However, we also find that loop corrections of short modes on the power spectrum of long modes, even though not large enough to violate perturbativity requirements, remain appreciable and, most importantly, are not tamed in realistic realisations of smooth SR/USR/SR transitions. This makes perturbativity a powerful theoretical tool to constrain USR dynamics. We extend the analysis at any scale beyond those relevant for CMB observations. We find that loop corrections of short modes remain within the few percent if compared to the tree-level power spectrum. However, we also find one notable exception of phenomenological relevance: we show that the so-called dip in the power spectrum of curvature perturbation is an artifact of the tree-level computation.

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G. Franciolini, A. Iovino, M. Taoso, et. al.
Mon, 8 May 23
14/63

Comments: 31 pages, 12 figures

Tilt-to-length coupling in LISA Pathfinder: analytical modelling [CL]

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http://arxiv.org/abs/2305.03667


Tilt-to-length coupling was the limiting noise source in LISA Pathfinder between 20 and 200 mHz before subtraction in post-processing. To prevent the adding of sensing noise to the data by the subtraction process, the success of this strategy depended on a previous direct noise reduction by test mass alignment. The exact dependency of the level of tilt-to-length coupling on the set-points of LISA Pathfinder’s test masses was not understood until the end of the mission. Here, we present, for the first time, an analytical tilt-to-length coupling model that describes the coupling noise changes due to the realignments. We report on the different mechanisms, namely the lever arm and piston effect as well as the coupling due to transmissive components, and how they contribute to the full coupling. Further, we show that a pure geometric model would not have been sufficient to describe the coupling in LISA Pathfinder. Therefore, we model also the non-geometric tilt-to-length noise contributions. For the resulting coupling coefficients of the full model, we compute the expected error bars based on the known individual error sources. Also, we validated the analytical model against numerical simulations. A detailed study and thorough understanding of this noise are the basis for a successful analysis of the LISA Pathfinder data with respect to tilt-to-length coupling.

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M. Hartig and G. Wanner
Mon, 8 May 23
15/63

Comments: N/A

Dark Matter-Induced Stellar Oscillations [CL]

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http://arxiv.org/abs/2305.03085


It has been hypothesized that dark matter is comprised of ultra-light bosons whose collective phenomena can be described as a scalar field undergoing coherent oscillations. Examples include axion and fuzzy dark matter models. In this ultra-light dark matter scenario, the harmonic variation in the field’s energy-momentum tensor sources an oscillating component of the gravitational potential that we show can resonantly-excite stellar oscillations. A mathematical framework for predicting the amplitude of these oscillations is developed, which reveals that ultra-light dark matter predominantly excites p-modes of degree $l=1$. An investigation of resonantly-excited solar oscillations is presented, from which we conclude that dark matter-induced oscillations of the Sun are likely undetectable. We discuss prospects for constraining ultra-light dark matter using other stellar objects.

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J. Sakstein and I. Saltas
Mon, 8 May 23
25/63

Comments: 5 pages, no figures. Comments welcome. A reproduction package for our numerical analysis is available here: this https URL

Tip of the Red Giant Branch Bounds on the Axion-Electron Coupling Revisited [CL]

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http://arxiv.org/abs/2305.03113


We present a novel method to constrain the axion-electron coupling constant using the observed calibration of the tip of the red giant branch (TRGB) I band magnitude $M_I$ that fully accounts for uncertainties and degeneracies with stellar input physics.~We simulate a grid of 116,250 models varying initial mass, helium abundance, and metallicity and train a machine learning emulator to predict $M_I$ as a function of these parameters.~Our emulator enables the use of Markov Chain Monte Carlo simulations where the axion-electron coupling $\alpha_{26}$ is varied simultaneously with the stellar parameters. We find that, once stellar uncertainties and degeneracies are accounted for, the region $\alpha_{26} < 2$ is not excluded by empirical TRGB calibrations.~Our work opens up a large region of parameter space currently believed to be excluded.~$\alpha_{26} = 2$ is the upper limit of the parameter space considered by this study, and it is likely that larger values of $\alpha_{26}$ are also unconstrained.~We discuss potential applications of our work to reevaluate other astrophysical probes of new physics.

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M. Dennis and J. Sakstein
Mon, 8 May 23
26/63

Comments: 14 pages, 6 figures, 1 table, dataset at this https URL

Black Holes as the source of the dark energy: a stringent test with the high-redshift JWST AGNs [CEA]

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http://arxiv.org/abs/2305.03408


It has been suggested that there is evidence for cosmological coupling of black holes (BHs) with an index of $k\approx 3$ and hence the BHs serve as the astrophysical source of the dark energy. The data sample however is limited for the redshifts $\leq 2.5$. Recently, the James Webb Space Telescope (JWST) has detected more than 180 high-redshift Active Galactic Nuclei (AGNs) and quasars. Among the JWST NIRSpec/NIRCam resolved AGNs, three are identified in early-type host galaxies with a redshift $z\sim 4.5-7$. Their $M_{\star}$ and $M_{\rm BH}$, however, are in tension with the prediction of the cosmological coupling of black holes with $k=3$ at a confidence level of $\sim 3\sigma$, which is not in support of the hypothesis that BHs serve as the origin of dark energy. The future observations of high-redshift AGNs by JWST will further test such a hypothesis by identifying more early-type host galaxies in the higher mass range.

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L. Lei, L. Zu, G. Yuan, et. al.
Mon, 8 May 23
40/63

Comments: 9 pages, 3 figures, 1 table; Submitted to ApJL. Comments are welcome!

Spectrogram correlated stacking: A novel time-frequency domain analysis of the Stochastic Gravitational Wave Background [CL]

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http://arxiv.org/abs/2305.03090


The astrophysical stochastic gravitational wave background (SGWB) originates from numerous faint sub-threshold gravitational wave (GW) signals arising from the coalescing binary compact objects. This background is expected to be discovered from the current (or next-generation) network of GW detectors by cross-correlating the signal between multiple pairs of GW detectors. However, detecting this signal is challenging and the correlation is only detectable at low frequencies due to the arrival time delay between different detectors. In this work, we propose a novel technique, \texttt{Spectrogram Correlated Stacking} (or \texttt{SpeCs}), which goes beyond the usual cross-correlation (and to higher frequencies) by exploiting the higher-order statistics in the time-frequency domain which accounts for the \textit{chirping} nature of the individual events that comprise SGWB. We show that \texttt{SpeCs} improves the signal-to-noise for the detection of SGWB by a factor close to $8$, compared to standard optimal cross-correlation methods which are tuned to measure only the power spectrum of the SGWB signal.\texttt{SpeCs} can probe beyond the power spectrum and its application to the GW data available from the current and next-generation GW detectors would speed up the SGWB discovery.

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R. Dey, L. Micchi, S. Mukherjee, et. al.
Mon, 8 May 23
44/63

Comments: N/A

Dissipative Genesis of the Inflationary Universe [CL]

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http://arxiv.org/abs/2305.02366


We study an inflation model with a flat scalar potential supported by observations and find that slow-roll inflation can emerge after a quasi-cyclic phase of the Universe, where it undergoes repeated expansions and contractions for a finite time period. The initial conditions and the positive spatial curvature required for such nontrivial dynamics align with the quantum creation of the Universe. The key ingredients that trigger inflation are dissipative interactions of the inflaton, which are necessary to reheat the Universe after inflation and thus give us an observational handle on pre-inflationary physics. Our discovery implies that inflation occurs more robustly after the creation.

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H. Matsui, A. Papageorgiou, F. Takahashi, et. al.
Fri, 5 May 23
8/67

Comments: 5 pages, 1 figure

Effect of Earth-Moon's gravity on TianQin's range acceleration noise. III. An analytical model [IMA]

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http://arxiv.org/abs/2305.02539


TianQin is a proposed space-based gravitational wave detector designed to operate in circular high Earth orbits. As a sequel to [Zhang et al. Phys. Rev. D 103, 062001 (2021)], this work provides an analytical model to account for the perturbing effect of the Earth’s gravity field on the range acceleration noise between two TianQin satellites. For such an “orbital noise,” the Earth’s contribution dominates above $5\times 10^{-5}$ Hz in the frequency spectrum, and the noise calibration and mitigation, if needed, can benefit from in-depth noise modeling. Our model derivation is based on Kaula’s theory of satellite gravimetry with Fourier-style decomposition, and uses circular reference orbits as an approximation. To validate the model, we compare the analytical and numerical results in two main scenarios. First, in the case of the Earth’s static gravity field, both noise spectra are shown to agree well with each other at various orbital inclinations and radii, confirming our previous numerical work while providing more insight. Second, the model is extended to incorporate the Earth’s time-variable gravity. Particularly relevant to TianQin, we augment the formulas to capture the disturbance from the Earth’s free oscillations triggered by earthquakes, of which the mode frequencies enter TianQin’s measurement band above 0.1 mHz. The analytical model may find applications in gravity environment monitoring and noise-reduction pipelines for TianQin.

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L. Jiao and X. Zhang
Fri, 5 May 23
19/67

Comments: 16 pages, 9 figures, accepted by Phys. Rev. D

Rotating neutron stars in the first order post-Newtonian approximation [HEAP]

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http://arxiv.org/abs/2305.02413


We study models of uniformly and differentially rotating neutron stars in the framework of post-Newtonian approximation in general relativity as established by Chandrasechar. In particular, we adopt the polytropic equation of state in order to derive the appropriate hydrodynamic equations and a rotation law based on the generalized Clement’s model. To compute equilibrium configurations at the mass-shedding limit, i.e. at critical angular velocity (equivalently, Keplerian angular velocity), we develop an iterative numerical method, belonging to the category of the well-known self-consistent field methods'', with two perturbation parameters: therotation parameter” $\bar{\upsilon}$ and the “gravitation or relativity parameter” $\bar{\sigma}$. These two parameters represent the effects of rotation and gravity on the configuration. We investigate the validity and the limits of our method by comparing our results with respective results of other computational methods and public domain codes. As it turns out, our method can derive satisfactory results for general-relativistic polytropic configurations at critical rotation.

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A. Fotopoulos, V. Karageorgopoulos and V. Geroyannis
Fri, 5 May 23
30/67

Comments: 28 pages, 6 Figures, 5 Tables, Submitted April 2023 Astronomy and Computing

Little Rip, Pseudo Rip and bounce cosmology from generalized equation of state in the Universe with spatial curvature [CL]

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http://arxiv.org/abs/2305.02796


We consider the Little Rip (LR), Pseudo Rip (PR) and bounce cosmological models in the Friedmann-Robertson-Walker (FRW) metric with nonzero spatial curvature. We describe the evolution of the universe using a generalized equation of state in the presence of a viscous fluid. The conditions of the occurrence of the LR, PR and bounce were obtained from the point of view of the parameters of the generalized equation of state for the cosmic dark fluid, taking into account the spatial curvature. The analytical expressions for the spatial curvature were obtained. Asymptotic cases of the early and late universe are considered. A method of Darboux transformation was proposed in the case of models of an accelerating universe with viscosity.

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A. A.V.Timoshkin and A. Yurov
Fri, 5 May 23
31/67

Comments: to appear in International Journal of Geometric Methods in Modern Physics

Is the Universe anisotropic right now? Comparing the real Universe with the Kasner's space-time [CL]

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http://arxiv.org/abs/2305.02726


We investigate possible astronomical manifestations of space-time anisotropy. The homogeneous vacuum Kasner solution was chosen as a reference anisotropic cosmological model because there are no effects caused by inhomogeneity in this simple model with a constant degree of anisotropy. This anisotropy cannot become weak. The study of its geodesic structure made it possible to clarify the properties of this space-time. It showed that the degree of manifestation of anisotropy varies significantly depending on the travel time of the light from the observed object. For nearby objects, for which it does not exceed half the age of the universe, the manifestations of anisotropy are very small. Distant objects show more pronounced manifestations, for example, in the distribution of objects over the sky and over photometric distances. These effects for each of the individual objects decrease with time, but in general, the manifestations of anisotropy in the Kasner space-time remain constant due to the fact that new sources emerging from beyond the cosmological horizon.We analyse observable signatures of the Kasner-type anisotropy and compare it to observations. These effects were not found in astronomical observations, including the study of the CMB. We can assume that the Universe has always been isotropic or almost isotropic since the recombination era. This does not exclude the possibility of its significant anisotropy at the moment of the Big Bang followed by rapid isotropization during the inflationary epoch.

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S. Parnovsky
Fri, 5 May 23
36/67

Comments: 18 pages, 2 figures