Tag Archives: General Relativity and Quantum Cosmology

A new approach and code for spinning black holes in modified gravity [CL]

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http://arxiv.org/abs/2212.07293


We discuss and implement a spectral method approach to computing stationary and axisymmetric black hole solutions and their properties in modified theories of gravity. The resulting code is written in the Julia language and is transparent and easily adapted to new settings. We test the code on both general relativity and on Einstein-Scalar-Gauss-Bonnet gravity. It is accurate and fast, converging on a spinning solution in these theories with tiny errors ($\sim \mathcal{O}\left(10^{-13}\right)$ in most cases) in a matter of seconds.

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P. Fernandes and D. Mulryne
Thu, 15 Dec 22
74/75

Comments: 40 pages, 14 figures. GitHub repository: this https URL

Relativistic matter bispectrum of cosmic structures on the light cone [CEA]

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http://arxiv.org/abs/2212.06799


Upcoming surveys of cosmic structures will probe scales close to the cosmological horizon, which opens up new opportunities for testing the cosmological concordance model to high accuracy. In particular, constraints on the squeezed bispectrum could rule out the single-field hypothesis during inflation. However, the squeezed bispectrum is also sensitive to dynamical effects of general relativity as well as interactions of matter with residual radiation from the early Universe. In this paper, we present a relativistic simulation pipeline that includes these relativistic effects consistently. We produce light cones and calculate the observed number counts of cold dark matter for five redshift bins between $z=0.55$-$2.25$. We compare the relativistic results against reference Newtonian simulations by means of angular power- and bispectra. We find that the dynamical relativistic effects scale roughly inversely proportional to the multipole in the angular power spectrum, with an amplitude of $0.5\%$ to $5\%$ of the total power. By using a smoothing method applied to the binned bispectrum we detect the Newtonian bispectrum with very high significance. The purely relativistic part of the matter bispectrum, obtained by subtracting the Newtonian bispectrum from the relativistic one, is detected with a significance of $\sim 3\,\sigma$, mostly limited by cosmic variance. Our relativistic pipeline for modelling ultra-large scales yields gauge-independent results as we compute observables consistently on the past light cone, while the Newtonian treatment employs approximations that leave some residual gauge dependence. A gauge-invariant approach is required in order to meet the expected level of precision of forthcoming probes of cosmic structures on ultra-large scales.

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T. Montandon, J. Adamek, O. Hahn, et. al.
Wed, 14 Dec 22
59/69

Comments: 38 pages, 14 figures

The MSPSR$π$ catalogue: VLBA astrometry of 18 millisecond pulsars [HEAP]

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http://arxiv.org/abs/2212.06351


With unparalleled rotational stability, millisecond pulsars (MSPs) serve as ideal laboratories for numerous astrophysical studies, many of which require precise knowledge of the distance and/or velocity of the MSP. Here, we present the astrometric results for 18 MSPs of the “MSPSR$\pi$” project focusing exclusively on astrometry of MSPs, which includes the re-analysis of 3 previously published sources. On top of a standardized data reduction protocol, more complex strategies (i.e., normal and inverse-referenced 1D interpolation) were employed where possible to further improve astrometric precision. We derived astrometric parameters using sterne, a new Bayesian astrometry inference package that allows the incorporation of prior information based on pulsar timing where applicable. We measured significant ($>3\,\sigma$) parallax-based distances for 15 MSPs, including $0.81\pm0.02\,$kpc for PSR J1518+4904 — the most significant model-independent distance ever measured for a double neutron star system. For each MSP with a well-constrained distance, we estimated its transverse space velocity and radial acceleration. Among the estimated radial accelerations, the updated ones of PSR J1012+5307 and PSR J1738+0333 impose new constraints on dipole gravitational radiation and the time derivative of Newton’s gravitational constant. Additionally, significant angular broadening was detected for PSR J1643-1224, which offers an independent check of the postulated association between the HII region Sh 2-27 and the main scattering screen of PSR J1643-1224. Finally, the upper limit of the death line of $\gamma$-ray-emitting pulsars is refined with the new radial acceleration of the hitherto least energetic $\gamma$-ray pulsar PSR J1730-2304.

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H. Ding, A. Deller, B. Stappers, et. al.
Wed, 14 Dec 22
62/69

Comments: 23 pages, 6 figures, 10 tables, accepted for publication in MNRAS

Aspects of Inflation and Cosmology in Non-Minimally Coupled and $R^{2}$ Palatini Gravity [CL]

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http://arxiv.org/abs/2212.06749


This thesis presents research exploring aspects of inflation and cosmology in the context of inflation models in which an inflaton is non-minimally coupled to the Ricci scalar, or is considered in conjunction with a term quadratic in the Ricci scalar. We consider a $\phi^{2}$ Palatini inflation model in $R^{2}$ gravity and investigate whether this model can overcome some of the problems of the original $\phi^{2}$ chaotic inflation model. We investigate the compatibility of this model with the observed CMB when treated as an effective theory of inflation in quantum gravity by examining the constraints on the model parameters arising due to Planck-suppressed potential corrections and reheating. Additionally, we consider two possible reheating channels and assess their viability in relation to the constraints on the size of the coupling to the $R^{2}$ term. We present an application of the Affleck-Dine mechanism, in which quadratic $B$-violating potential terms generate the asymmetry, with a complex inflaton as the Affleck-Dine field. We derive the $B$ asymmetry generated in the inflaton condensate analytically and numerically. We use the present-day asymmetry to constrain the size of the $B$-violating mass term and derive an upper bound on the inflaton mass in order for the Affleck-Dine dynamics to be compatible with non-minimally coupled inflation in the metric and Palatini formalisms. We demonstrate the existence of a new class of inflatonic Q-balls in a non-minimally coupled Palatini inflation model, through an analytical derivation of the Q-ball equation and numerical confirmation of the existence of solutions, and derive a range of the inflaton mass squared within which the model can inflate and produce Q-balls. We derive analytical estimates of the properties of these Q-balls, explore the effects of curvature, and discuss observational signatures of the model.

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K. Lloyd-Stubbs
Wed, 14 Dec 22
63/69

Comments: PhD Thesis, 286 pages, 28 figures

Testing Horndeski gravity with S2 star orbit [CL]

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http://arxiv.org/abs/2212.05082


We have explored a completely new and alternative way to restrict the parameter space of Horndeski theory of gravity. Using its Newtonian limit, it is possible to test the theory at a regime where, given its complexity and the small magnitude of the expected effects, it is poorly probed. At Newtonian level, it gives rise to a generalized Yukawa-like Newtonian potential which we have tested using S2 star orbit data. Our model adds five parameters to the General Relativity model, and the analysis constrains two of them with unprecedented precision to these energy scales, while only gives an exclusion region for the remaining parameters. We have shown the potential of weak-field tests to constrain Horndeski gravity opening, as a matter of fact, a new avenue that deserves to be further, and deeply, explored near in the future.

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R. Monica, I. Martino, D. Vernieri, et. al.
Tue, 13 Dec 22
9/105

Comments: 8 pages, 4 figures, 3 tables, 1 supplementary figure. Accepted for publication on MNRAS

Reconciling a decelerating Universe with cosmological observations [CL]

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http://arxiv.org/abs/2212.05568


Can modern cosmological observations be reconciled with a general-relativistic Universe without an anti-gravitating energy source? Usually, the answer to this question by cosmologists is in the negative, and it is commonly believed that the observed excess dimming of supernovae relative to that in the Milne model is evidence for dark energy. In this paper, we develop a theorem that clarifies the conditions for such an excess dimming, based on which we argue that the answer to the above question may counter-intuitively be `yes’.

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A. Heinesen
Tue, 13 Dec 22
11/105

Comments: 5 pages

From Cosmic Inflation and Matter Creation to Dark Matter – Journey of the Inflaton? [CL]

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http://arxiv.org/abs/2212.06117


A scenario of the inflaton evolution from cosmic inflation and matter creation to dark energy/dark matter today is presented. To start with, a model of the inflationary phase of the inflaton is discussed. The inflaton rolls down a simple quadratic hilltop potential along with matter creation, following an exact tracking solution of its dynamics. Being dragged down by the presence of matter, it rolls down slowly and naturally ending inflation as the universe stops accelerating due to the presence of matter. The model predictions for the standard metrics such as scalar/tensor spectral indexes and tensor to scalar ratio are fully consistent with the current CMB limits. The quadratic potential could be extended to complete a potential hill subsequent to inflation. The evolution of inflaton discussed recently is consistent with this picture of its journey from cosmic inflation to dark matter today.

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B. Balakrishna
Tue, 13 Dec 22
13/105

Comments: arXiv admin note: text overlap with arXiv:2210.15475

Constraining the bispectrum from bouncing cosmologies with Planck [CEA]

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http://arxiv.org/abs/2212.05977


Bouncing models of cosmology, as they arise e.g. in loop quantum cosmology, can generate close-to-scale-invariant fluctuation spectra as observed in the Cosmic Microwave Background (CMB). However, they are typically not Gaussian and also generate a bispectrum. It was proposed that these models can help to mitigate the large-scale anomalies of the CMB by considering large non-Gaussianities on very large scales, which decay exponentially on sub-horizon scales. It was therefore thought that this non-Gaussianity would not be visible in observations, which can only probe sub-horizon scales. In this letter we show that bouncing models with parameters such that they can mitigate the large-scale anomalies of the CMB are excluded by the Planck data with high significance of, depending on the specific model, $6.4$ or $14$ standard deviations.

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B. Tent, P. Delgado and R. Durrer
Tue, 13 Dec 22
22/105

Comments: 5 pages, 1 figure

Gravitational waves from the early universe [CEA]

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http://arxiv.org/abs/2212.05594


These lecture notes are based on the course “Gravitational waves from the early universe” given at the 27th W.E. Heraeus “Saalburg” Summer School 2021 by Valerie Domcke. Ongoing and future collaborations will probe different frequency ranges of the gravitational wave spectrum, allowing for probing different stages of the early universe and Beyond Standard Model physics. Due to the very high energies involved, accelerators cannot probe them. Therefore, current knowledge about new physics is limited and relies on bounds from CMB observations and theoretical assumptions about these energy scales. While some models are in tension with CMB data, others are unconstrained in shorter wavelength scales. Nonetheless, each one of these models has a gravitational wave density spectrum that can be compared to data. These lecture notes review the formalism of gravitational waves in General Relativity and introduce stochastic gravitational waves, primordial sources, and detection efforts.

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R. Santos and L. Manen
Tue, 13 Dec 22
38/105

Comments: Submission to SciPost

Accretion-modified stellar-mass black hole distribution and milli-Hz gravitational wave backgrounds from galaxy centre [HEAP]

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http://arxiv.org/abs/2212.05724


Gas accretion of embedded stellar-mass black holes\,(sBHs) or stars in the accretion disk of active galactic nuclei\,(AGNs) will modify the mass distribution of these sBHs and stars, which will also affect the migration of the sBHs/stars. \textbf{With the introduction of the mass accretion effect, we simulate the evolution of the sBH/star distribution function in a consistent way by extending the Fokker-Planck equation of sBH/star distributions to the mass-varying scenario, and explore the mass distribution of sBHs in the nuclear region of the galaxy centre.} We find that the sBHs can grow up to several tens solar mass and form heavier sBH binaries, which will be helpful for us to understand the black-hole mass distribution as observed by the current and future ground-based gravitational wave detectors\,(e.g., LIGO/VIRGO, ET and Cosmic Explorer). We further estimate the event rate of extreme mass-ratio inspirals\,(EMRI) for sBH surrounding the massive black hole and calculate the stochastic gravitational wave\,(GW) background of the EMRIs. We find that the background can be detected in future space-borne GW detectors after considering the sBHs embedded in the AGN disk, while the mass accretion has a slight effect on the GW background.

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M. Wang, Y. Ma and Q. Wu
Tue, 13 Dec 22
42/105

Comments: 15 pages, 8 figures

Towards a reliable reconstruction of the power spectrum of primordial curvature perturbation on small scales from GWTC-3 [CEA]

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http://arxiv.org/abs/2212.05516


Primordial black holes (PBHs) can be both candidates of dark matter and progenitors of binary black holes (BBHs) detected by the LIGO-Virgo-KAGRA collaboration. Since PBHs could form in the very early Universe through the gravitational collapse of primordial density perturbations, the population of BBHs detected by gravitational waves encodes much information on primordial curvature perturbation. In this work, we take a reliable and systematic approach to reconstruct the power spectrum of the primordial curvature perturbation from GWTC-3, under the hierarchical Bayesian inference framework, by accounting for the measurement uncertainties and selection effects. In addition to just considering the single PBH population model, we also report the results considering the multi-population model, i.e., the mixed PBH and astrophysical black hole binaries model. We find that the maximum amplitude of the reconstructed power spectrum of primordial curvature perturbation can be $\sim2.5\times10^{-2}$ at $\mathcal{O}(10^{5})~\rm Mpc^{-1}$ scales, which is consistent with the PBH formation scenario from inflation at small scales.

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L. Zheng, Z. Li, Z. Chen, et. al.
Tue, 13 Dec 22
46/105

Comments: N/A

Gravity from the Determinant of the Energy-Momentum: Astrophysical Implications [CL]

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http://arxiv.org/abs/2212.05585


Determinants of the second-rank tensors stand useful in forming generally invariant terms as in the case of the volume element of the gravitational actions. Here, we extend the action of the matter fields by an arbitrary function $f(D)$ of the determinants of their energy-momentum, and the metric, $D=|\textbf{det}.T|/|\textbf{det}.g|$. We derive the gravitational field equations and examine the nonlinear terms induced by the determinant, specifically, the inverse of the energy-momentum tensor. We also show that these extensions require a nonzero stress-energy tensor for the vacuum. We propose a scale-free model, $f(D)=\lambda D^{1/4}$, and show how it induces the familiar invariant terms formed by the trace of the energy-momentum tensor by expanding the action around the stress-energy of the vacuum. We study the hydrostatic equilibrium equations for a neutron star by providing relevant values of the dimensionless constant $\lambda$. We show that the differences from the predictions of general relativity, in the mass-radius relations, which are sensitive to the equations of state, are conspicuous for $\lambda \sim -10^{-2}$. We also show that the model does not affect the predictions on the primordial nucleosynthesis when it is applied to the early radiation era. This novel and unfamiliar type of gravity-matter coupling can lead to a rich phenomenology in gravitational physics.

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H. Azri and S. Nasri
Tue, 13 Dec 22
49/105

Comments: to appear in PLB

Horizon thermodynamics and cosmological equations: A holographic-like connection between thermostatistical quantities on a cosmological horizon and in the bulk [CL]

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http://arxiv.org/abs/2212.05822


Horizon thermodynamics is expected to be related to the effective energy based on the energy density calculated from the Friedmann equation for a Friedmann–Robertson–Walker (FRW) universe. In the present study, the effective energy and thermostatistical quantities on a cosmological horizon are examined to clarify the holographic-like connection between them, with a focus on a de Sitter universe. To this end, the Helmholtz free energy on the horizon is derived from horizon thermodynamics. The free energy is found to be equivalent to the effective energy calculated from the Friedmann equation. This consistency is interpreted as a kind of holographic-like connection. To examine this connection, Padmanabhan’s holographic equipartition law, which is related to the origin of spacetime dynamics, is applied to a de Sitter universe. It is found that the law should lead to a holographic-like connection. The holographic-like connection is considered to be a bridge between thermostatistical quantities on the horizon and in the bulk. For example, cosmological equations for a flat FRW universe can be derived from horizon thermodynamics by accepting the connection as a viable scenario. In addition, a thermal entropy equivalent to the Bekenstein–Hawking entropy is obtained from the Friedmann equation using the concept of a canonical ensemble in statistical physics. The present study provides new insight into the discussion of horizon thermodynamics and cosmological equations.

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N. Komatsu
Tue, 13 Dec 22
65/105

Comments: 10 pages

Black hole solutions in the quadratic Weyl conformal geometric theory of gravity [CL]

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http://arxiv.org/abs/2212.05542


We consider numerical black hole solutions in the Weyl conformal geometry, and its associated conformally invariant Weyl quadratic gravity. In this model Einstein gravity (with a positive cosmological constant) is recovered in the spontaneously broken phase of Weyl gravity, after the Weyl gauge field ($\omega _{\mu}$) becomes massive through a Stueckelberg mechanism, and it decouples. As a first step in our investigations we write down the conformally invariant gravitational action, containing a scalar degree of freedom, and the Weyl vector. The field equations are derived from the variational principle in the absence of matter. By adopting a static spherically symmetric geometry, the vacuum field equations for the gravitational, scalar, and Weyl fields are obtained. After reformulating the field equations in a dimensionless form, and by introducing a suitable independent radial coordinate, we obtain their solutions numerically. We detect the formation of a black hole from the presence of a Killing horizon for the timelike Killing vector in the metric tensor components, indicating the existence of the singularity in the metric. Several models, corresponding to different functional forms of the Weyl vector, are considered. An exact black hole model, corresponding to a Weyl vector having only a radial spacelike component, is also obtained. The thermodynamic properties of the Weyl geometric type black holes (horizon temperature, specific heat, entropy and evaporation time due to Hawking luminosity) are also analyzed in detail.

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J. Yang, S. Shahidi and T. Harko
Tue, 13 Dec 22
71/105

Comments: 29 pages, 13 figures, accepted for publication in EPJC

Solving the Teukolsky equation with physics-informed neural networks [CL]

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http://arxiv.org/abs/2212.06103


We use physics-informed neural networks (PINNs) to compute the first quasi-normal modes of the Kerr geometry via the Teukolsky equation. This technique allows us to extract the complex frequencies and separation constants of the equation without the need for sophisticated numerical techniques, and with an almost immediate implementation under the \texttt{PyTorch} framework. We are able to compute the oscillation frequencies and damping times for arbitrary black hole spins and masses, with accuracy typically below the percentual level as compared to the accepted values in the literature. We find that PINN-computed quasi-normal modes are indistinguishable from those obtained through existing methods at signal-to-noise ratios (SNRs) larger than 100, making the former reliable for gravitational-wave data analysis in the mid term, before the arrival of third-generation detectors like LISA or the Einstein Telescope, where SNRs of ${\cal O}(1000)$ might be achieved.

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R. Luna, J. Bustillo, J. Martínez, et. al.
Tue, 13 Dec 22
76/105

Comments: 12 pages, 7 figures

Quantum field corrections to the equation of state of freely streaming matter in the Friedman-Robertson-Walker space-time [CL]

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http://arxiv.org/abs/2212.05518


We calculate the expectation value of the energy density and pressure of a scalar field after its decoupling from a thermal bath in the spatially flat Friedman-Robertson-Walker space-time, within the framework of quantum statistical mechanics. By using the density operator determined by the condition of local thermodynamic equilibrium, we determine the mean value of the stress-energy tensor of a real scalar field by subtracting the vacuum expectation value at the time of the decoupling. The obtained expressions of energy density and pressure involve corrections with respect to the classical free-streaming solution of the relativistic Boltzmann equation, which may become relevant even at long times.

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F. Becattini and D. Roselli
Tue, 13 Dec 22
80/105

Comments: 16 pages, 1 figure

Modified propagation of gravitational waves from the early radiation era [CL]

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http://arxiv.org/abs/2212.06082


We study the propagation of cosmological gravitational wave (GW) backgrounds from the early radiation era until the present day in modified theories of gravity. Comparing to general relativity (GR), we study the effects that Horndeski parameters, such as the run rate of the effective Planck mass $\alpha_{\rm M}$ and the tensor speed excess $\alpha_{\rm T}$, have on the present-day GW spectrum. We use both the WKB estimate, which provides an analytical description but fails at superhorizon scales, and numerical simulations that allow us to go beyond the WKB approximation. We show that $\alpha_{\rm T}$ makes relatively insignificant changes to the GR solution, especially taking into account the constraints on its value from GW observations by the LIGO-Virgo collaboration, while $\alpha_{\rm M}$ can introduce modifications to the spectral slopes of the GW energy spectrum in the low-frequency regime depending on the considered time evolution of $\alpha_{\rm M}$. The latter effect is additional to the damping or growth occurring equally at all scales that can be predicted by the WKB approximation. In light of the recent observations by pulsar timing array collaborations and future detectors such as SKA, LISA, DECIGO, BBO, or ET, we show that, in most of the cases, constraints can not be placed on the effects of $\alpha_{\rm M}$ and the initial GW energy density $\mathcal{E}_{\rm GW}^*$ separately, but only on the combined effects of the two.

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Y. He, A. Pol and A. Brandenburg
Tue, 13 Dec 22
83/105

Comments: 31 pages, 11 figures, 2 tables

Cosmic voids are emptier in the presence of symmetron's domain walls [CEA]

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http://arxiv.org/abs/2212.06119


The symmetron field has an environment (density) dependent behavior which is a common feature of the models with the screening mechanism and results in a rich phenomenology. This model can produce domain walls between regions with different densities. We consider this aspect and study the physics of domain walls in between (underdensity) voids and (overdensity) halo structures. The (spherical) domain walls exert a repulsive force on a test mass outside of the wall while a test mass inside of the wall sees no force. This makes the structures outside the voids go further to a larger radius. Effectively, this means the voids are becoming larger in this scenario in comparison to the standard model of cosmology. Interestingly, this makes voids emptier which may shed light on Peebles’ void phenomenon.

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B. Nosrati and N. Khosravi
Tue, 13 Dec 22
97/105

Comments: 7 pages, 4 figures, comments are welcome

An update on adiabatic modes in cosmology and $δ$N formalism [CEA]

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http://arxiv.org/abs/2212.05112


In this paper, we generalize the Weinberg’s procedure to determine the comoving curvature perturbation $\cal R$ to non-attractor inflationary regimes. We show that both modes of $\cal R$ are related to a symmetry of the perturbative equations in the Newtonian gauge. As a byproduct, we clarify that adiabaticity does not generally imply constancy of $\cal R$, not even in the $k\rightarrow 0$ limit. Applying this knowledge to the separate Universe approach, we find that correlators of $\delta N$ {\it do not} generically correspond to comoving curvature perturbations correlators, even at the linear level, but rather to correlators of curvature perturbations at uniform density, at least at linear level. Thus, $\delta N$ formalism does not capture information about decaying (for slow-roll) or growing (beyond slow-roll) modes of $\cal R$. The latter being the only interesting mode for models of inflation related to primordial black holes formation.

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D. Cruces, C. Germani and A. Palomares
Tue, 13 Dec 22
99/105

Comments: 15 pages, 1 figure

Metric-affine effects in crystallization processes of white dwarfs [CL]

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http://arxiv.org/abs/2212.04918


We analyze the effects of modified gravity on specific heats of electrons and ions, Debye temperature, crystallization process, and cooling mechanism in white dwarfs. We derive the Lane-Emden-Chandrasekhar equation and relate it to the cooling process equations for Palatini $f(R)$ gravity. Moreover, for the first time in the literature, we show that the gravity model plays a crucial role not only in the mass and size of the white dwarf, but also affects their internal properties. We further demonstrate that modified gravity can decrease the cooling age significantly.

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S. Kalita, L. Sarmah and A. Wojnar
Tue, 13 Dec 22
101/105

Comments: 11 pages with 8 figures; comments welcome

A unified model for the LISA measurements and instrument simulations [CL]

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http://arxiv.org/abs/2212.05351


LISA is a space-based mHz gravitational-wave observatory, with a planned launch in 2034. It is expected to be the first detector of its kind, and will present unique challenges in instrumentation and data analysis. An accurate pre-flight simulation of LISA data is a vital part of the development of both the instrument and the analysis methods. The simulation must include a detailed model of the full measurement and analysis chain, capturing the main features that affect the instrument performance and processing algorithms. Here, we propose a new model that includes, for the first time, proper relativistic treatment of reference frames with realistic orbits; a model for onboard clocks and clock synchronization measurements; proper modeling of total laser frequencies, including laser locking, frequency planning and Doppler shifts; better treatment of onboard processing and updated noise models. We then introduce two implementations of this model, LISANode and LISA Instrument. We demonstrate that TDI processing successfully recovers gravitational-wave signals from the significantly more realistic and complex simulated data. LISANode and LISA Instrument are already widely used by the LISA community and, for example, currently provide the mock data for the LISA Data Challenges.

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J. Bayle and O. Hartwig
Tue, 13 Dec 22
103/105

Comments: 27 pages, 16 figures, 3 tables

Formulating the r-mode problem for slowly rotating neutron stars [CL]

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http://arxiv.org/abs/2212.04837


We revisit the problem of inertial r-modes in stratified stars, drawing on a more precise description of the composition stratification in a mature neutron star. The results highlight issues with the traditional approach to the problem, leading us to rethink the computational strategy for r-modes of non-barotropic neutron stars. We outline two strategies for dealing with the problem. For moderate to slowly rotating neutron stars the only viable alternative may be to approach the problem numerically from the outset, while a meaningful slow-rotation calculation can be carried out for the fastest known spinning stars (which may be close to being driven unstable by the emission of gravitational waves). We demonstrate that the latter approach leads to a problem close, but not identical, to that for barotropic inertial modes. We also suggest that these reformulations of the problem likely resolve the long-standing problem of singular behaviour associated with a co-rotation point in rotating relativistic neutron stars. This issue needs to be resolved in order to guide future gravitational-wave searches.

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N. Andersson and F. Gittins
Mon, 12 Dec 22
1/52

Comments: 22 pages, 1 figure

Parameter Estimation for Stellar-Origin Black Hole Mergers In LISA [CL]

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http://arxiv.org/abs/2212.04600


The population of stellar origin black hole binaries (SOBHBs) detected by existing ground-based gravitational wave detectors is an exciting target for the future space-based Laser Interferometer Space Antenna (LISA). LISA is sensitive to signals at significantly lower frequencies than ground-based detectors. SOBHB signals will thus be detected much earlier in their evolution, years to decades before they merge. The mergers will then occur in the frequency band covered by ground-based detectors. Observing SOBHBs years before merger can help distinguish between progenitor models for these systems. We present a new Bayesian parameter estimation algorithm for LISA observations of SOBHBs that uses a time-frequency (wavelet) based likelihood function. Our technique accelerates the analysis by several orders of magnitude compared to the standard frequency domain approach and allows for an efficient treatment of non-stationary noise.

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M. Digman and N. Cornish
Mon, 12 Dec 22
21/52

Comments: 13 pages, 6 figures, 1 table

The r-modes of slowly rotating, stratified neutron stars [CL]

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http://arxiv.org/abs/2212.04892


The only r-modes that exist in a globally barotropic, rotating, Newtonian star are the fundamental $l = |m|$ solutions, where $l$ and $m$ are the indices of the spherical harmonic $Y_l^m$ that describe the mode’s angular dependence. This is in stark contrast to a stellar model that is non-barotropic throughout its interior, which hosts all the $l \geq |m|$ perturbations including radial overtones. In reality, neutron stars are stratified with locally barotropic regions. Therefore, we explore how stratification alters a star’s ability to support r-modes. We consider the globally stratified case and examine the behaviour of the modes as the star gets close to barotropicity. In this limit, we find that all but the fundamental $l = |m|$ perturbations change character and become generic inertial modes. Restricting the analysis to $l = |m|$ perturbations, we develop the r-mode equations in order to consider stellar models that exhibit local barotropicity. Our results for such models show that the r-mode overtones diverge and join the inertial modes. This suggests that neutron stars can only support the fundamental $l = |m|$ r-modes.

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F. Gittins and N. Andersson
Mon, 12 Dec 22
25/52

Comments: 15 pages, 8 figures

A fractal LTB model cannot explain Dark Energy [CEA]

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http://arxiv.org/abs/2212.04529


We revisited the problem of describing, on average, a fractal distribution of matter using a Lemaitre-Tolman-Bondi (LTB) solution. Here we study the fractal structure of our local universe having a fractal dimension and a scale transition. We test our model with the latest type Ia supernova data, the Pantheon compilation, and discuss problems and possible improvements for it, concluding that a fractal transition in LTB cosmology cannot be used to explain the effects of dark energy but it can be useful to study structures at low scales.

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E. Pastén and V. Cárdenas
Mon, 12 Dec 22
33/52

Comments: N/A

Growth of Cosmic Structure [CEA]

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http://arxiv.org/abs/2212.05003


We review one of the most fruitful areas in cosmology today that bridge theory and data – the temporal growth of large-scale structure. We go over the growth’s physical foundations, and derive its behavior in simple cosmological models. While doing so, we explain how measurements of growth can be used to understand theory. We then review how some of the most mature cosmological probes – galaxy clustering, gravitational lensing, the abundance of clusters of galaxies, cosmic velocities, and cosmic microwave background – can be used to probe the growth of structure. We report the current constraints on growth, which are summarized as measurements of the parameter combination $f\sigma_8$ as a function of redshift, or else as the mass fluctuation amplitude parameter $S_8$. We finally illustrate several statistical approaches, ranging from the “growth index” parameterization to more general comparisons of growth and geometry, that can sharply test the standard cosmological model and indicate the presence of modifications to general relativity.

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D. Huterer
Mon, 12 Dec 22
39/52

Comments: Invited review for The Astronomy and Astrophysics Review, aimed at a non-expert; 29 pages + references

Microlensing effects of blackhole-like wormholes [CL]

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http://arxiv.org/abs/2211.17065


In this paper, we investigate the microlensing effects of blackhole-like wormholes. We evaluate the deflection angle upon the second order under weak field approximation with Gauss-Bonnet theorem. We elaborate on the deflection angle of the Ellis-Bronnikov wormhole as an example. Following the same procedure, we study the magnification of three typical wormholes (WH): Schwarzschild WH, Kerr-like WH, and RN WH, as well as their blackhole correspondence. We find that the prograde case of Kerr-like metric will lead to the multi-peaks of magnification as the mass part is compatible with the charge part. Moreover, the first two gentle peaks of Kerr blackhole are larger than the wormhole case by one order of magnitude, while the main peak of Kerr blackholes and wormholes are of the same order. For other cases, the behavior of magnification wormholes and their corresponding blackholes is similar. Our result may shed new light on exploring compact objects through the microlensing effect.

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K. Gao, L. Liu and M. Zhu
Mon, 12 Dec 22
45/52

Comments: 10 pages, 11 figures, references updated, typos corrected

Detecting massive scalar fields with Extreme Mass-Ratio Inspirals [CL]

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http://arxiv.org/abs/2212.03888


We study the imprint of light scalar fields on gravitational waves from extreme mass ratio inspirals — binary systems with a very large mass asymmetry. We first show that, to leading order in the mass ratio, any effects of the scalar on the waveform are captured fully by two parameters: the mass of the scalar and the scalar charge of the secondary compact object. We then use this theory-agnostic framework to show that the future observations by LISA will be able to simultaneously measure both of these parameters with enough accuracy to detect ultra-light scalars.

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S. Barsanti, A. Maselli, T. Sotiriou, et. al.
Fri, 9 Dec 22
25/75

Comments: 11 pages, 7 figures

Observational Constraints on Warm Natural Inflation [CL]

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http://arxiv.org/abs/2212.04482


Warm natural inflation is studied for the case of the original cosine potential. The radiation bath during inflation induces a dissipation (friction) rate in the equation of motion for the inflaton field, which can potentially reduce the field excursion needed for an observationally viable period of inflation. We examine if the dissipation thus provides a mechanism to avoid the large decay constant $f \gtrsim M_{\mathrm{pl}}$ of cold cosine natural inflation. Whereas temperature independent dissipation has previously been shown to alleviate the need for a trans-Planckian decay constant $f$, we illustrate here the difficulties of accommodating a significantly sub-Planckian decay constant ($f<10^{-1}M_{\mathrm{pl}}$) in the case of the following temperature dependent dissipation rates, $\Gamma \propto T^c$, with $c={1,3}$. Such dissipation rates represent physically well-motivated constructions in the literature. For each model, we map its location in the $r$-$n_s$ plane and compare with Cosmic Microwave Background data. For $c=1 \, (c=3)$, we find that agreement with CMB data requires that dissipation be in the weak (moderate) regime and that the minimum allowed value of the decay constant in the potential is $f_{\rm min} = 0.3 \, (0.8)\,M_{\mathrm{pl}}$ respectively.

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G. Montefalcone, V. Aragam, L. Visinelli, et. al.
Fri, 9 Dec 22
43/75

Comments: 23 pages, 3 figures, 1 table

Speed Variations of Cosmic Photons and Neutrinos from Loop Quantum Gravity [CL]

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http://arxiv.org/abs/2212.04220


Recently a series of analyses on the flight time of cosmic photons and neutrinos suggests that the speed of light \emph{in vacuo} takes the energy-dependent form $v(E)\simeq 1-E/E_{\text{LIV}}^{\gamma }$ with $E_{\text{LIV}}^{\gamma }\approx 3.6\times 10^{17}~\text{GeV}$, and meanwhile the speed of neutrinos is proposed to be $v(E)\simeq 1\pm E/E_{\text{LIV}}^{\nu }$ with $E_{\text{LIV}}^{\nu }\approx 6.5\times 10^{17}~\text{GeV}$ and $\pm {}$ representing the helicity dependence. This novel picture immediately urges us to provide a satisfactory theoretical explanation. Among all the attempts to predict the speed variations from quantum gravity, we find that loop quantum gravity can serve as a good candidate for explaining the aforementioned picture consistently.

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H. Li and B. Ma
Fri, 9 Dec 22
46/75

Comments: 6 latex pages, final version for journal publication

Can high-redshift Hubble diagrams rule out the standard model of cosmology in the context of cosmographic method? [CEA]

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http://arxiv.org/abs/2212.04118


Using mock data for the Hubble diagrams of type Ia supernovae (SNIa) and quasars (QSOs) generated based on the standard model of cosmology, and using the least-squares method based on the Markov-Chain-Monte-Carlo (MCMC) algorithm, we first put constraints on the cosmographic parameters in the context of the various model-independent cosmographic methods reconstructed from the Taylor $4^{th}$ and $5^{th}$ order expansions and the Pade (2,2) and (3,2) polynomials of the Hubble parameter, respectively. We then reconstruct the distance modulus in the framework of cosmographic methods and calculate the percentage difference between the distance modulus of the cosmographic methods and that of the standard model. The percentage difference is minimized when the Pade approximation is used which means that the Pade cosmographic method is sufficiently suitable for reconstructing the distance modulus even at high-redshifts. In the next step, using the real observational data for the Hubble diagrams of SNIa, QSOs, gamma-ray-bursts (GRBs), and observations from baryon acoustic oscillations (BAO) in two sets of the low-redshift combination (SNIa+QSOs+GRBs+BAO) embracing the redshift range of $0.01<z<2.26$ and the high-redshift combination (SNIa+QSOs+GRBs) which covers a redshift range of $0.01< z < 5.5$, we put observational constraints on the cosmographic parameters of the Pade cosmography and also the standard model. Our analysis indicates that Pade cosmographic approaches do not reveal any cosmographic tension between the standard model and the observational data. We also confirm this result, using the statistical AIC criteria. Finally, we put the cosmographic method in the redshift-bin data and find a larger value of $\Omega_{m0}$ extracted from $s_0$ parameter compared with those of the $q_0$ parameter and Planck-$\Lambda$CDM values.

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S. Pourojaghi, N. Zabihi and M. Malekjani
Fri, 9 Dec 22
53/75

Comments: 17 pages, 8 figures, 7 tables. accepted in PRD

Exploring High Frequency Gravitational Waves with Magnons [CL]

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http://arxiv.org/abs/2212.04094


Detecting gravitational waves with a frequency higher than 10 kHz requires a new idea. In previous papers, we proposed magnon gravitational wave detectors and gave the first limit on GHz gravitational waves by reinterpreting the existing data of axion dark matter experiments. In this paper, we show that the sensitivity can be improved by constructing the detector specific to gravitational waves. In particular, we employ an infinite sum of terms in the expansion of Fermi normal coordinates to probe gravitational waves with a wavelength comparable to the detector size. As a consequence, we obtain the sensitivity around $h_c \sim 10^{-20}$.

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A. Ito and J. Soda
Fri, 9 Dec 22
67/75

Comments: 13 pages, 2 figures

f(T) cosmology against the cosmographic method: A new study using mock and observational data [CEA]

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http://arxiv.org/abs/2212.04113


In this paper, we study the power-law $f(T)$ model using Hubble diagrams of type Ia supernovae (SNIa), quasars (QSOs), Gamma Ray Bursts (GRBs) and the measurements from baryonic acoustic oscillations (BAO) in the framework of the cosmographic method. Using mock data for SNIa, QSOs and GRBs generated based on the power-law $f(T)$ model, we show whether different cosmographic methods are suitable to reconstruct the distance modulus or not. In particular, we investigate the rational PADE polynomials $(3,2)$ and $(2,2)$ in addition to the fourth- and fifth- order Taylor series. We show that PADE $(3,2)$ is the best approximation that can be used in the cosmographic method to reconstruct the distance modulus at both low and high redshifts. In the context of PADE $(3,2)$ cosmographic method, we show that the power-law $f(T)$ model is well consistent with the real observational data from the Hubble diagrams of SNIa, QSOs and GRBs. Moreover, we find that the combination of the Hubble diagram of SNIa and the BAO observation leads to better consistency between the model-independent cosmographic method and the power-law $f(T)$ model. Finally, our observational constraints on the parameter of the effective equation of state of DE, described by the power-law $f(T)$ model, show the phantom-like behavior, especially when the BAO observations are included in our analysis.

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M. Sabiee, M. Malekjani and D. Jassur
Fri, 9 Dec 22
68/75

Comments: 19 pages, 10 figures, 6 tables

An Effective Sign Switching Dark Energy: Lotka-Volterra Model of Two Interacting Fluids [CL]

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http://arxiv.org/abs/2212.04429


One of the recent attempts to address the Hubble and $\sigma_8$ tensions is to consider the Universe started out not as a de Sitter-like spacetime, but rather anti-de Sitter-like. That is, the Universe underwent an “AdS-to-dS” transition at some point. We study the possibility that there are two dark energy fluids, one of which gave rise to the anti-de Sitter-like early Universe. The interaction is modeled by the Lotka-Volterra equations, commonly used in population biology. We consider “competition” models that are further classified as “unfair competition” and “fair competition”. The former involves a quintessence in competition with a phantom, and the second involves two phantom fluids. Surprisingly, even in the latter scenario it is possible for the overall dark energy to cross the phantom divide. The latter model also allows a constant $w$ “AdS-to-dS” transition, thus serving as a counter-example to the claim that such a dark energy must possess a singular equation of state. We also consider a “conversion” model in which a phantom fluid still manages to achieve “AdS-to-dS” transition even if it is being converted into a negative energy density quintessence. In these models, the energy density of the late time effective dark energy is related to the coefficient of the quadratic self-interaction term of the fluids, which is analogous to the resource capacity in population biology.

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Y. Ong
Fri, 9 Dec 22
69/75

Comments: N/A

Adiabatic expansion for varying speed of light model [CEA]

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http://arxiv.org/abs/2212.03728


Recently, we proposed a varying speed of light (VSL) model to solve various late-time cosmological problems \cite{Lee:2020zts}. This model has one free parameter, $b$, to characterize the time variation of the speed of light as a function of a scale factor, $c = c_0a^{b/4}$. Time variations of various physical constants and quantities have different powers of scale factor as a function of $b$ to satisfy all known local physics laws, including special relativity, thermodynamics, and electromagnetic force. This model is based on the Robertson-Walker metric and satisfies the isotropic and homogeneous 3-space required by the cosmological principle. Adiabaticity is a necessary condition to keep homogeneity and isotropy because a net energy flux would falsify the isotropy if there is a preferential energy flow direction. It also might forge homogeneity if the outward (inward) flux is isotropic. Thus, any VSL model should also preserve an adiabatic expansion condition to be a viable model. Also, it provides an additional condition for constraining physical constants.

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S. Lee
Thu, 8 Dec 22
7/63

Comments: 5 pages, 3 tables

Incompatibility of Standard Galaxy Bias Models in General Relativity [CL]

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http://arxiv.org/abs/2212.03573


The standard model for galaxy bias is built in a Newtonian framework, and several attempts have been made in the past to put it in a relativistic framework. The focus of past works was, however, to use the same Newtonian formulation, but to provide its interpretation in a relativistic framework by either fixing a gauge condition or transforming to a local coordinate system. Here we demonstrate that these reverse-engineered approaches fail, because they do not respect the diffeomorphism symmetry in general relativity. Hence we need to take a different approach to the problem and develop a covariant formulation of galaxy bias model that is diffeomorphism compatible. We consider a simple toy model for galaxy bias and discuss the implication for measuring the primordial non-Gaussianity by using the flawed standard model for galaxy bias.

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J. Yoo
Thu, 8 Dec 22
22/63

Comments: 6 pages, 1 figure, comments are welcome

Primordial black holes generated by the non-minimal spectator field [CEA]

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http://arxiv.org/abs/2212.03577


In this paper, we propose a model in which a spectator field non-minimally couples to an inflaton field and the power spectrum of the perturbation of the spectator field at small scales is dramatically enhanced by the sharp feature in the form of non-minimal coupling. At or after the end of inflation, the perturbation of the spectator field is converted into curvature perturbation and leads to the formation of primordial black holes (PBHs). Furthermore, for example, we consider three phenomenological models for generating PBHs with mass function peaked at $\sim10^{-12}M_\odot$ and representing all the cold dark matter in our Universe and find that the scalar induced gravitational waves generated by the curvature perturbation can be detected by the future space-borne gravitational-wave detectors such as Taiji, TianQin and LISA.

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D. Meng, C. Yuan and Q. Huang
Thu, 8 Dec 22
30/63

Comments: 15 pages and 4 figures

Model independent bounds for the number of $e$-folds during the evolution of the universe [CL]

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http://arxiv.org/abs/2212.03730


We present a simple procedure to obtain universal bounds for quantities of cosmological interest, such as the number of $e$-folds during inflation, reheating, and radiation, as well as the reheating temperature. The main assumption is to represent each of the various epochs of evolution of the universe as being due to a single substance changing instantaneously into the next, describing a new era of evolution of the universe. This assumption, commonly used to obtain solutions of the Friedmann equations for simple cosmological models, is implemented here to find model-independent bounds on cosmological quantities of interest. In particular, we find that the bound $N_k\approx 56$ for $-\frac{1}{3} < \omega_{re} < \frac{1}{3}$ is very robust as an upper bound on the number of $e$-folds during inflation and also as a lower bound when $\omega_{re} > \frac{1}{3}$, where $\omega_{re}$ is the effective equation of state parameter during reheating. These are model-independent results that any single-field model of inflation should satisfy. As an example, we illustrate the two approaches with the basic $\alpha$ attractor model and show how they complement each other.

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G. German, R. Quaglia and A. Colorado
Thu, 8 Dec 22
34/63

Comments: 17 pages, 3 figures, 2 tables

Scattering of neutrinos by a rotating black hole accounting for the electroweak interaction with an accretion disk [CL]

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http://arxiv.org/abs/2212.03479


We study spin effects in the neutrino gravitational scattering by a supermassive black hole with a magnetized accretion disk having a finite thickness. We exactly describe the propagation of ultrarelativistic neutrinos on null geodesics and solve the spin precession equation along each neutrino trajectory. The interaction of neutrinos with the magnetic field is owing to the nonzero diagonal magnetic moment. Additionally, neutrinos interact with plasma of the accretion disk electroweakly within the Fermi approximation. These interactions are obtained to change the polarization of incoming neutrinos, which are left particles. The fluxes of scattered neutrinos, proportional to the survival probability of spin oscillations, are derived for various parameters of the system. In particular, we are focused on the matter influence on the outgoing neutrinos flux. The possibility to observe the predicted effects for astrophysical neutrinos is briefly discussed.

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M. Dvornikov
Thu, 8 Dec 22
40/63

Comments: 14 pages in LaTeX2e, 14 eps figures

When Love fades away: Modelling frequency-dependent tidal deformability for environmental black-hole mergers [CL]

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http://arxiv.org/abs/2212.03343


Motivated by events in which black holes can lose their environment due to tidal interactions in a binary system, we develop a waveform model in which the tidal deformability interpolates between a finite value (dressed black hole) at relatively low frequency and a zero value (naked black hole) at high frequency. We then apply this model to the example case of a black hole dressed with an ultralight scalar field and investigate the detectability of the tidal Love number with the Einstein Telescope. We show that the parameters of the tidal deformability model could be measured with high accuracy, providing a useful tool to understand dynamical environmental effects taking place during the inspiral of a binary system.

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V. Luca, A. Maselli and P. Pani
Thu, 8 Dec 22
54/63

Comments: 7 pages, 3 figures

Generation of Primordial Black Holes from inflation model with modified dispersion relation [CEA]

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http://arxiv.org/abs/2212.03403


Primordial black hole (PBHs) is interesting to people for its ability of explaining dark matter as well as supermassive astrophysical objects. In normal inflation scenario, the generation of PBHs usually requires enhanced power spectrum of scalar perturbation at the end of inflation era, which is expected when the dispersion relation of the inflaton field gets modified. In this work, we study a kind of inflation model called “{\it DBI-inspired non-minimal kinetic coupling” (DINKIC)} model, where the dispersion relation is modified by a square root existing in the field Lagrangian. We discuss the enhancement of scalar power spectrum due to the modified dispersion relation, as well as the abundance of PBHs produced by the Press-Schechter collapse mechanism. We also discuss the formation of Scalar-Induced Gravitational Waves (SIGWs) by linear scalar perturbations.

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T. Qiu and W. Zheng
Thu, 8 Dec 22
56/63

Comments: 12 pages, 5 figures

Modified gravity and cosmology with nonminimal (derivative) coupling between matter and the Einstein tensor [CL]

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http://arxiv.org/abs/2212.03821


We construct new classes of modified theories in which the matter sector couples with the Einstein tensor, namely we consider direct couplings of the latter to the energy-momentum tensor, and to the derivatives of its trace. We extract the general field equations and we apply them in a cosmological framework, obtaining the Friedmann equations, whose extra terms give rise to an effective dark energy sector. At the background level we show that we can successfully describe the usual thermal history of the universe, with the sequence of matter and dark-energy epochs, while the dark-energy equation-of-state parameter can lie in the phantom regime, tending progressively to -1 at present and future times. Furthermore, we confront the theory with Cosmic Chronometer data, showing that the agreement is very good. Finally, we perform a detailed investigation of scalar and tensor perturbations, and extracting an approximate evolution equation for the matter overdensity we show that the predicted behavior is in agreement with observations.

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P. Asimakis, S. Basilakos, A. Lymperis, et. al.
Thu, 8 Dec 22
57/63

Comments: 9 pages,4 figures

Detectability of Sub-Solar Mass Neutron Stars Through a Template Bank Search [HEAP]

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http://arxiv.org/abs/2212.03855


We study the detectability of gravitational-wave signals from sub-solar mass binary neutron star systems by the current generation of ground-based gravitational-wave detectors. We find that finite size effects from large tidal deformabilities of the neutron stars and lower merger frequencies can significantly impact the sensitivity of the detectors to these sources. By simulating a matched-filter based search using injected binary neutron star signals with tidal deformabilities derived from physically motivated equations of state, we calculate the reduction in sensitivity of the detectors. We conclude that the loss in sensitive volume can be as high as $78.4 \%$ for an equal mass binary system of chirp mass $0.17 \, \textrm{M}_{\odot}$, in a search conducted using binary black hole template banks. We use this loss in sensitive volume, in combination with the results from the search for sub-solar mass binaries conducted on data collected by the LIGO-Virgo observatories during their first three observing runs, to obtain a conservative upper limit on the merger rate of sub-solar mass binary neutron stars. Since the discovery of a low-mass neutron star would provide new insight into formation mechanisms of neutron stars and further constrain the equation of state of dense nuclear matter, our result merits a dedicated search for sub-solar mass binary neutron star signals.

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A. Bandopadhyay, B. Reed, S. Padamata, et. al.
Thu, 8 Dec 22
62/63

Comments: 11 pages, 7 figures, supplemental materials at this https URL

Observing axions through photon ring dimming of black holes [CL]

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http://arxiv.org/abs/2212.03020


It is known that magnetic fields exist near black holes and photons can go around the black holes due to strong gravity. Utilizing these facts, we can probe hypothetical pseudoscalar particles, so-called axions. In fact, photons can be converted into axions when they propagate in a magnetic field. The conversion of such photons into axions leads to a dimming of the photon ring around the black hole shadow. We show that the photon ring dimming can occur efficiently for supermassive black holes. Remarkably, it turns out that the maximal dimming rate of the photon ring is 25%. In the case of M87$^*$, the dimming could be around 10% in the X-ray and gamma-ray bands. The frequency band and the magnitude of the dimming depend on the axion-photon coupling and axion mass. Hence, the distorted spectrum of the photon ring provides a novel tool for detecting axions.

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K. Nomura, K. Saito and J. Soda
Wed, 7 Dec 22
2/74

Comments: 17 pages, 4 figures

Stringent Pulsar Timing Bounds on Light Scalar Couplings to Matter [CL]

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http://arxiv.org/abs/2212.03098


Pulsar Timing constraints on scalar-tensor theories with conformal and disformal couplings to matter are discussed. Reducing the dynamics to the motion in the centre of mass frame and using the mean anomaly parametrisation, we find the first post-Newtonian corrections induced by the conformal and disformal interactions in the form of a generalized quasi-Keplerian solution. We also derive the radiation reaction force due to scalar radiation and the corresponding Post-Keplerian Parameters (PKP). We use different pulsar time of arrival (TOA) data sets to probe the scalar corrections to the PKP. In particular, we focus on systems with large orbital frequencies as the contributions to the PKP terms induced by the disformal coupling are sensitive to higher frequencies. We find that the most constraining pulsar timing events are PSR B1913+16 and the double pulsar PSR J0737-3039A/B, being stronger than the Cassini bound on the conformal coupling obtained from the Shapiro effect in the solar system. The combined constraints using other pulsar events give an upper bound on the conformal coupling $\beta^2 < 2.3 \cdot 10^{-5}$ and a lower bound on the disformal coupling scale of $\Lambda \sim 1 \ {\rm MeV}$ which is comparable to the Cassini bound and to the GW-170817 constraints respectively. Future measurements for pulsar timing with black hole companions are also discussed.

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D. Benisty, P. Brax and A. Davis
Wed, 7 Dec 22
16/74

Comments: 17 pages, 9 figures

Large Deviations in the Early Universe [CL]

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http://arxiv.org/abs/2212.02535


Fluctuations play a critical role in cosmology. They are relevant across a range of phenomena from the dynamics of inflation to the formation of structure. In many cases, these fluctuations are coarse grained and follow a Gaussian distribution as a consequence of the Central Limit Theorem. Yet, some classes of observables are dominated by rare fluctuations and are sensitive to the details of the underlying microphysics. In this paper, we argue that the Large Deviation Principle can be used to diagnose when one must to appeal to the fundamental description. Concretely, we investigate the regime of validity for the Fokker-Planck equation that governs Stochastic Inflation. For typical fluctuations, this framework leads to the central limit-type behavior expected of a random walk. However, fluctuations in the regime of the Large Deviation Principle are determined by instanton-like saddle points accompanied by a new energy scale. When this energy scale is above the UV cutoff of the EFT, the tail is only calculable in the microscopic description. We explicitly demonstrate this phenomenon in the context of determining the phase transition to eternal inflation, the distribution of scalar field fluctuations in de Sitter, and the production of primordial black holes.

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T. Cohen, D. Green and A. Premkumar
Wed, 7 Dec 22
17/74

Comments: 32 pages + references, 3 figures

Numerical analyses of M31 dark matter profiles [CL]

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http://arxiv.org/abs/2212.02999


We reproduce the rotation curve of the Andromeda galaxy (M31) by taking into account its bulge, disk, and halo components, considering the last one to contain the major part of dark matter mass. Hence, our prescription is to split the galactic bulge into two components, namely, the inner and main bulges, respectively. Both bulges are thus modeled by exponential density profiles since we underline that the widely accepted de Vaucouleurs law fails to reproduce the whole galactic bulge rotation curve. In addition, we adopt various well-known phenomenological dark matter profiles to estimate the dark matter mass in the halo region. Moreover, we apply the least-squares fitting method to determine from the rotation curve the model free parameters, namely, the characteristic (central) density, scale radius, and consequently the total mass. To do so, we perform Markov chain Monte Carlo statistical analyses based on the Metropolis algorithm, maximizing our likelihoods adopting velocity and radii data points of the rotation curves. We do not fit separately the components for bulges, disk and halo, but we perform an overall fit including all the components and employing all the data points. Thus, we critically analyze our corresponding findings and, in particular, we employ the Bayesian Information Criterion to assess the most accredited model to describe M31 dark matter dynamics.

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K. Boshkayev, T. Konysbayev, Y. Kurmanov, et. al.
Wed, 7 Dec 22
20/74

Comments: 10 pages, 7 figures and 7 tables

On the LISA science performance in observations of short-lived signals from massive black hole binary coalescences [CL]

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http://arxiv.org/abs/2212.02572


The observation of massive black hole binary systems is one of the main science objectives of the Laser Interferometer Space Antenna (LISA). The instrument’s design requirements have recently been revised: they set a requirement at $0.1\,\mathrm{mHz}$, with no additional explicit requirements at lower frequencies. This has implications for observations of the short-lived signals produced by the coalescence of massive and high-redshift binaries. Here we consider the most pessimistic scenario: the (unlikely) case in which LISA has no sensitivity below $0.1\,\mathrm{mHz}$. We show that the presence of higher multipoles (beyond the dominant $\ell = |m| = 2$ mode) in the gravitational radiation from these systems, which will be detectable with a total signal-to-noise ratio $\sim 10^3$, allows LISA to retain the capability to accurately measure the physical parameters, the redshift, and to constrain the sky location. To illustrate this point, we consider a few select binaries in a total (redshifted) mass range of $4 \times10^6 – 4 \times 10^7\,M_\odot$ whose ($\ell = |m| = 2$) gravitational-wave signals last between $\approx 12$ hours and $\approx 20$ days in band. We model the emitted gravitational radiation using the highly accurate (spin-aligned) waveform approximant IMRPhenomXHM and carry out a fully coherent Bayesian analysis on the LISA noise-orthogonal time-delay-interferometry channels.

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G. Pratten, A. Klein, C. Moore, et. al.
Wed, 7 Dec 22
31/74

Comments: 13 pages, 6 figures, comments welcome!

Spatially Homogeneous Universes with Late-Time Anisotropy [CEA]

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http://arxiv.org/abs/2212.03234


The Cosmological Principle asserts that on sufficiently large scales the universe is homogeneous and isotropic on spatial slices. Challenging this principle requires a departure from the FLRW ansatz. In this paper we analyse the cosmological evolution of spatially homogeneous but anisotropic universes in which only two of the three space dimensions are maximally symmetric, namely the closed Kantowski-Sachs universe and the open axisymmetric Bianchi type III universe. These models are characterised by two scale factors and we study their evolution in universes with radiation, matter and a cosmological constant. In all cases, the two scale factors evolve differently and this anisotropy leads to a lensing effect in the propagation of light. We derive explicit formulae for computing redshifts, angular diameter distances and luminosity distances and discuss the predictions of these models in relation to observations for type Ia supernovae and the CMB.

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A. Constantin, T. Harvey, S. Hausegger, et. al.
Wed, 7 Dec 22
52/74

Comments: N/A

Boson stars and their relatives in semiclassical gravity [CL]

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http://arxiv.org/abs/2212.02530


We construct boson star configurations in quantum field theory using the semiclassical gravity approximation. Restricting our attention to the static case, we show that the semiclassical Einstein-Klein-Gordon system for a {\it single real quantum} scalar field whose state describes the excitation of $N$ {\it identical particles}, each one corresponding to a given energy level, can be reduced to the Einstein-Klein-Gordon system for $N$ {\it complex classical} scalar fields. Particular consideration is given to the spherically symmetric static scenario, where energy levels are labeled by quantum numbers $n$, $\ell$ and $m$. When all particles are accommodated in the ground state $n=\ell=m=0$, one recovers the standard static boson star solutions, that can be excited if $n\neq 0$. On the other hand, for the case where all particles have fixed radial and total angular momentum numbers $n$ and $\ell$, with $\ell\neq 0$, but are homogeneously distributed with respect to their magnetic number $m$, one obtains the $\ell$-boson stars, whereas when $\ell=m=0$ and $n$ takes multiple values, the multi-state boson star solutions are obtained. Further generalizations of these configurations are presented, including the multi-$\ell$ multi-state boson stars, that constitute the most general solutions to the $N$-particle, static, spherically symmetric, semiclassical real Einstein-Klein-Gordon system, in which the total number of particles is definite. In spite of the fact that the same spacetime configurations also appear in multi-field classical theories, in semiclassical gravity they arise naturally as the quantum fluctuations associated with the state of a single field describing a many-body system. Our results could have potential impact on direct detection experiments in the context of ultralight scalar field/fuzzy dark matter candidates.

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M. Alcubierre, J. Barranco, A. Bernal, et. al.
Wed, 7 Dec 22
70/74

Comments: 21 pages, 1 figure, 3 tables

Dynamics of interacting monomial scalar field potentials and perfect fluids [CL]

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http://arxiv.org/abs/2212.02942


Motivated by cosmological models of the early universe we analyse the dynamics of the Einstein equations with a minimally coupled scalar field with monomial potentials $V(\phi)=\frac{(\lambda\phi)^{2n}}{2n}$, $\lambda>0$, $n\in\mathbb{N}$, interacting with a perfect fluid with linear equation of state $p_\mathrm{pf}=(\gamma_\mathrm{pf}-1)\rho_\mathrm{pf}$, $\gamma_\mathrm{pf}\in(0,2)$, in flat Robertson-Walker spacetimes. The interaction is a friction-like term of the form $\Gamma(\phi)=\mu \phi^{2p}$, $\mu>0$, $p\in\mathbb{N}\cup{0}$. The analysis relies on the introduction of a new regular 3-dimensional dynamical systems’ formulation of the Einstein equations on a compact state space, and the use of dynamical systems’ tools such as quasi-homogeneous blow-ups and averaging methods involving a time-dependent perturbation parameter. We find a bifurcation at $p=n/2$ due to the influence of the interaction term. In general, this term has more impact on the future (past) asymptotics for $p<n/2$ ($p>n/2$). For $p<n/2$ we find a complexity of possible future attractors, which depends on whether $p=(n-1)/2$ or $p<(n-1)/2$. In the first case the future dynamics is governed by Li\’enard systems. On the other hand when $p=(n-2)/2$ the generic future attractor consists of new solutions previously unknown in the literature which can drive future acceleration whereas the case $p<(n-2)/2$ has a generic future attractor de-Sitter solution. For $p=n/2$ the future asymptotics can be either fluid dominated or have an oscillatory behaviour where neither the fluid nor the scalar field dominates. For $p>n/2$ the future asymptotics is similar to the case with no interaction. Finally, we show that irrespective of the parameters, an inflationary quasi-de-Sitter solution always exists towards the past, and therefore the cases with $p\leq(n-2)/2$ may provide new cosmological models of quintessential inflation.

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A. Alho, V. Bessa and F. Mena
Wed, 7 Dec 22
71/74

Comments: 63 pages, 54 figures

An exponential equation of state of dark energy in the light of 2018 CMB Planck data [CEA]

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http://arxiv.org/abs/2212.01974


The dynamics of the Universe is analyzed using an exponential function for the dark energy equation of state, known as Gong-Zhang parameterization. The phase space of the free parameters presented in the model is constrained using Cosmic Microwave Background radiation, Cosmic Chronometers, modulus distance from Hydrogen II Galaxies, Type Ia Supernovae and measurements from Baryon Acoustic Oscillations, together with a stronger bound from a Joint analysis. The cosmological model is confronted with $\Lambda$CDM, observing there is a strong evidence for $\Lambda$CDM in the Joint analysis although the exponential model is preferred when the data are separated. Based on the Joint analysis, a value of $\omega_0 = -1.202^{+0.027}{-0.026}$ is found for the characteristic parameter presented in the equation of state. Additionally, the cosmographic parameters at current times are reported, having $q_0 = -0.789^{+0.034}{-0.036}$, $j_0=1.779^{+0.130}{-0.119}$, and a transition deceleration-acceleration redshift $z_T = 0.644^{+0.011}{-0.012}$. Furthermore, the age of the Universe is estimated as $t_U = 13.788^{+0.019}_{-0.019}$ Gyrs. Finally, under the $\mathbf{\mathbb{H}}0(z)$ diagnostic, we discuss this model could alleviate the $H_0$ tension.

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M. Castillo-Santos, A. Hernández-Almada, M. García-Aspeitia, et. al.
Tue, 6 Dec 22
1/87

Comments: Submitted in MNRAS

Gravitational lens system as a potential tool to detect extremely low frequency primordial gravitational wave [CL]

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http://arxiv.org/abs/2212.02221


The imprint of extremely low frequency primordial gravitational wave on a gravitational lens system with a non-aligned source-deflector-observer configuration is investigated in work (Liu, 2022, MNRAS, 517, 2769) from which it shows that time delay with perturbation from extremely low frequency primordial gravitational wave could deviate from the one deduced from the theoretical model as much as 100 percent with a series of chosen parameters. However, the frequency of gravitational wave chosen in work (Liu, 2022, MNRAS, 517, 2769) is a little bit confusing. Here, with the suitable parameters chosen in this work, the results show that time delay between different images of the source in the gravitational lens system with perturbation from primordial gravitational wave with extremely low frequency could strongly deviate from the one resulting from the theoretical model as much as about several hundred percent, indicating that time delay from gravitational lens system could be used to detect extremely low frequency primordial gravitational wave.

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W. Liu
Tue, 6 Dec 22
9/87

Comments: 3 pages, 1 figure

A revised formalism for slowly-rotating superfluid neutron stars in general relativity [CL]

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http://arxiv.org/abs/2212.02390


We discuss slowly-rotating, general relativistic, superfluid neutron stars in the Hartle-Thorne formulation. The composition of the stars is described by a simple two-fluid model which accounts for superfluid neutrons and all other constituents. We apply a perturbed matching framework to derive a new formalism for slowly-rotating superfluid neutron stars, valid up to second-order perturbation theory, building on the original formulation reported by Andersson and Comer in 2001. The present study constitutes an extension of previous work in the single-fluid case where it was shown that the Hartle-Thorne formalism needs to be amended since it does not provide the correct results when the energy density does not vanish at the surface of the star. We discuss in detail the corrections that need to be applied to the original two-fluid formalism in order to account for non vanishing energy densities at the boundary. In the process, we also find a correction needed in the computation of the deformation of the stellar surface in the original two-fluid model in all cases (irrespective of the value of the energy density at the surface). The discrepancies found between the two formalisms are illustrated by building numerical stellar models, focusing on the comparison in the calculation of the stellar mass, the deformation of the star, and in the Kepler limit of rotation. In particular, using a toy-model equation of state for which the energy density does not vanish at the boundary of the star we demonstrate that the corrections to the formalism we find impact the structure of slowly-rotating superfluid neutron stars in a significant way.

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E. Aranguren, J. Font, N. Sanchis-Gual, et. al.
Tue, 6 Dec 22
10/87

Comments: 24 pages, 16 figures

Hubble constant by natural selection: Evolution chips in the Hubble tension [CEA]

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http://arxiv.org/abs/2212.02203


The Approximate Bayesian Computation (ABC) algorithm considers natural selection in biology as a guiding principle for statistical model selection and parameter estimation. We take this ABC approach to cosmology and use it to infer which model anchored on a choice of a Hubble constant prior would be preferred by the data. We find in all of our runs that the Planck Hubble constant ($H_0 = 67.4 \pm 0.5$ km s$^{-1}$Mpc$^{-1}$) always emerge naturally selected by the ABC over the SH$0$ES estimate ($H_0 = 73.30 \pm 1.04$ km s$^{-1}$Mpc$^{-1}$). The result holds regardless of how we mix our data sets, including supernovae, cosmic chronometers, baryon acoustic oscillations, and growth data. Compared with the traditional MCMC, we find that the ABC always results with narrower cosmological constraints, but remain consistent inside the corresponding MCMC posteriors.

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R. Bernardo and Y. Lee
Tue, 6 Dec 22
19/87

Comments: 11 pages, 5 figures, comments welcome

Improved binary black hole searches through better discrimination against noise transients [CL]

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http://arxiv.org/abs/2212.02026


The short-duration noise transients in LIGO and Virgo detectors significantly affect the search sensitivity of compact binary coalescence (CBC) signals, especially in the high mass region. In the previous work by the authors \cite{Joshi_2021}, a $\chi^2$ statistic was proposed to distinguish them from CBCs. This work is an extension where we demonstrate the improved noise-discrimination of the optimal $\chi^2$ statistic in real LIGO data. The tuning of the optimal $\chi^2$ includes accounting for the phase of the CBC signal and a well informed choice of sine-Gaussian basis vectors to discern how CBC signals and some of the most worrisome noise-transients project differently on them~\cite{sunil_2022}. We take real blip glitches (a type of short-duration noise disturbance) from the second observational (O2) run of LIGO-Hanford and LIGO-Livingston detectors. The binary black hole signals were simulated using \textsc{IMRPhenomPv2} waveform and injected into real LIGO data from the same run. We show that in comparison to the traditional $\chi^2$, the optimal $\chi^2$ improves the signal detection rate by around 4\% in a lower-mass bin ($m_1,m_2 \in [20,40]M_{\odot}$) and by more than 5\% in a higher-mass bin ($m_1,m_2 \in [60,80]M_{\odot}$), at a false alarm probability of $10^{-3}$. We find that the optimal $\chi^2$ also achieves significant improvement over the sine-Gaussian $\chi^2$.

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S. Choudhary, S. Bose, P. Joshi, et. al.
Tue, 6 Dec 22
38/87

Comments: 12pages, 6 figures

Shadows and Strong Gravitational Lensing by Van der Waals Black Hole in Homogeneous Plasma [CL]

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http://arxiv.org/abs/2212.02104


In this paper, we first analyze the horizon structure of the Van der Waals(VdW) black hole and then investigate its shadow in the absence of a plasma medium as well as the presence of a homogeneous plasma medium. We find that both the Van der Waals parameters $a$ and $b$ have a significant effect on the shadow of the black hole. We also observe that the radius of the shadow in a homogeneous plasma medium decreases while parameter $\sigma =\frac{\omega_p}{\omega_{\infty}}$ ( the ratio of plasma frequency and photon frequency) increases and the radius of the shadow inhomogeneous plasma medium is larger than the vacuum medium. We also discuss the strong gravitational lensing in a homogeneous plasma medium. We observe that the photon sphere radius, deflection limit coefficients and deflection angle in the strong field are highly affected by the presence of a homogeneous plasma medium. We also find that the deflection angle in the strong field limit by the Van der Waals black hole with the homogeneous plasma is greater than that of the Vacuum medium. Further, we discuss the observables quantities angular position $\theta_{\infty}$, separation $S$ and magnification $r_{mag}$ by taking the example of a supermassive black hole in the strong field limit with the effects of homogeneous plasma. It is concluded that the Van der Waals parameters $a$, $b$ and homogeneous plasma medium have a significant effect on both the shadows and strong gravitational lensing.

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N. Molla and U. Debnath
Tue, 6 Dec 22
44/87

Comments: 22 pages,34 figures

Searching for Intelligent Life in Gravitational Wave Signals Part I: Present Capabilities and Future Horizons [IMA]

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http://arxiv.org/abs/2212.02065


We show that the Laser Interferometer Gravitational Wave Observatory (LIGO) is a powerful instrument in the Search for Extra-Terrestrial Intelligence (SETI). LIGO’s ability to detect gravitational waves (GWs) from accelerating astrophysical sources, such as binary black holes, also provides the potential to detect extra-terrestrial mega-technology, such as Rapid And/or Massive Accelerating spacecraft (RAMAcraft). We show that LIGO is sensitive to RAMAcraft of $1$ Jupiter mass accelerating to a fraction of the speed of light (e.g. $10\%$) up to about $100\,{\rm kpc}$. Existing SETI searches probe on the order of thousands to tens of thousands of stars for human-scale technology (e.g. radiowaves), whereas LIGO can probe all $10^{11}$ stars in the Milky Way for RAMAcraft. Moreover, thanks to the $f^{-1}$ scaling of the GW signal produced by these sources, our sensitivity to these objects will increase as low-frequency, space-based detectors are developed and improved. In particular, we find that DECIGO and the Big Bang Observer (BBO) will be about 100 times more sensitive than LIGO, increasing the search volume by 10$^{6}$. In this paper, we calculate the waveforms for linearly accelerating RAMAcraft in a form suitable for LIGO, Virgo, or KAGRA searches and provide the range for a variety of possible masses and accelerations. We expect that the current and upcoming GW detectors will soon become an excellent complement to the existing SETI efforts.

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L. Sellers, A. Bobrick, G. Martire, et. al.
Tue, 6 Dec 22
63/87

Comments: 18 pages, 12 figures, to be submitted to MNRAS, comments welcome

A Finite Element Method for Angular Discretization of the Radiation Transport Equation on Spherical Geodesic Grids [CL]

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http://arxiv.org/abs/2212.01409


Discrete ordinate ($S_N$) and filtered spherical harmonics ($FP_N$) based schemes have been proven to be robust and accurate in solving the Boltzmann transport equation but they have their own strengths and weaknesses in different physical scenarios. We present a new method based on a finite element approach in angle that combines the strengths of both methods and mitigates their disadvantages. The angular variables are specified on a spherical geodesic grid with functions on the sphere being represented using a finite element basis. A positivity-preserving limiting strategy is employed to prevent non-physical values from appearing in the solutions. The resulting method is then compared with both $S_N$ and $FP_N$ schemes using four test problems and is found to perform well when one of the other methods fail.

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M. Bhattacharyya and D. Radice
Tue, 6 Dec 22
82/87

Comments: 24 pages, 13 figures

Impact of generalized holonomy corrections on the cosmological primordial power spectra [CL]

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http://arxiv.org/abs/2212.01182


The propagation of perturbations is studied with generalized holonomy corrections in a fully consistent way, ensuring that the deformed algebra of constraints remain closed. The primordial cosmological power spectra are calculated. It is shown that, although the detailed form of the correction does unavoidably impact the observables, the main known results of loop quantum cosmology are robust in this respect.

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M. Sousa, K. Martineau, C. Renevey, et. al.
Mon, 5 Dec 22
11/63

Comments: N/A

Scalar-Induced Gravitational Waves in a $Λ$CDM Cosmology [CEA]

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http://arxiv.org/abs/2212.01190


We reconsider the gravitational wave spectrum induced by scalar perturbations in spatially flat Friedmann-Lema\^itre-Robertson-Walker spacetimes, focusing on the matter- and $\Lambda$-dominated epochs. During matter domination, sub-horizon modes are not free and a commonly applied approximation for the derivative of the tensor perturbation is flawed. We show analytically that this leads to a significant overestimation of the energy density spectrum. In addition, we demonstrate that gauge-dependent non-oscillating tensor perturbations appear in the presence of a cosmological constant. Complementing the analytical calculations, we compute the according present-day spectrum numerically for a Planck-like $\Lambda$CDM cosmology, finding that non-oscillating growing modes appear during the transition between matter and $\Lambda$ domination in conformal Newtonian gauge.

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M. Sipp and B. Schaefer
Mon, 5 Dec 22
27/63

Comments: 11 pages, 4 figures

Transitioning from a bounce to $R^2$ inflation [CL]

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http://arxiv.org/abs/2212.01093


Non-singular bouncing cosmologies are well–motivated models for the early universe. Recent observational data are consistent with positive spatial curvature and allow for a natural collapsing and bouncing phase in the very early universe. Additionally, bouncing cosmologies have the potential to rectify conceptual shortcomings identified in the theory of inflation, such as the singularity problem. In this paper we present a classical bouncing model in the context of modified gravity, including an $R^2$-term in the action. We show that after the bounce, the universe enters naturally a period of inflation, driven by the $R^2$–term. We analyse the stability of the model and find that the scalaron assists the stability of the model.

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R. Daniel, M. Campbell, C. Bruck, et. al.
Mon, 5 Dec 22
30/63

Comments: 19 pages, 8 figures

Regularization in cosmological spacetimes without infrared distortions [CL]

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http://arxiv.org/abs/2212.01078


We reexamine the regularization of the two-point function of a scalar field in a Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime. Adiabatic regularization provides a set of subtraction terms in momentum space that successfully remove its ultraviolet divergences at coincident points, but can significantly distort the power spectrum at infrared scales, especially for light fields. In this work we propose, by using the intrinsic ambiguities of the renormalization program, a new set of subtraction terms that minimize the distortions for scales $k \lesssim M$, with $M$ an arbitrary mass scale. Our method is consistent with local covariance and equivalent to general regularization methods in curved spacetime. We apply our results to the regularization of the power spectrum in de Sitter space: while the adiabatic scheme yields exactly $\Delta_{\phi}^{\rm (reg)} = 0$ for a massless field, our proposed prescription recovers the standard scale-invariant result $\Delta_{\phi}^{\rm (reg)} \simeq H^2 /(4\pi^2)$ at super-horizon scales.

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A. Ferreiro and F. Torrenti
Mon, 5 Dec 22
34/63

Comments: 5 pages + references, 1 figure

The solar system test for the general modified gravity theories [CL]

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http://arxiv.org/abs/2212.01019


In the past few decades, various versions of modified gravity theories were proposed to mimic the effect of dark matter. Compared with the conventional Newtonian or relativistic dynamics, these theories contain some extra apparent force terms in the dynamical equations to replace the role of dark matter. Generally speaking, the extra apparent force terms usually scale with radius so that the effect would be significant only on large scale to explain the missing mass in galaxies or galaxy clusters. Nevertheless, the apparent effect may still be observable in small structures like the solar system. In this article, we derive analytic general formulae to represent the contribution of the precession angle of the planets in the solar system due to the general modified gravity theories, in which the extra apparent force terms can be written in a power law of radius $r$ or an exponential function in $r$. We have tested three popular modified gravity theories, the Modified Newtonian Dynamics (MOND), the Emergent Gravity (EG), and the Modified Gravity (MOG). In particular, based on the solar system data, we have constrained the parameters involved for two popular general interpolating functions used in MOND. Our results can be generally applied to both of the modified inertia and modified gravity versions of MOND.

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M. Chan and C. Lee
Mon, 5 Dec 22
58/63

Comments: Accepted in MNRAS

Distinct signatures of spinning PBH domination and evaporation: doubly peaked gravitational waves, dark relics and CMB complementarity [CEA]

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http://arxiv.org/abs/2212.00775


Ultra-low mass primordial black holes (PBH) which may briefly dominate the enegy density of the universe but completely evaporate before the big bang nucleosynthesis (BBN), can lead to interesting observable signatures. In our previous work, we studied the generation of a doubly peaked spectrum of induced stochastic gravitational wave background (ISGWB) for such a scenario and explored the possibility of probing a class of baryogenesis models wherein the emission of massive unstable particles from the PBH evaporation and their subsequent decay contributes to the matter-antimatter asymmetry. In this work, we extend the scope of our earlier work by including spinning PBHs and consider the emission of light relativistic dark sector particles, which contribute to the dark radiation (DR) and massive stable dark sector particles, thereby accounting for the dark matter (DM) component of the universe. The ISGWB can be used to probe the non-thermal production of these heavy DM particles, which cannot be accessible in any laboratory searches. For the case of DR, we find a novel complementarity between the measurements of $\Delta N_{\rm eff}$ from these emitted particles and the ISGWB from PBH domination. Our results indicate that the ISGWB has a weak dependence on the initial PBH spin. However, for gravitons as the DR particles, the initial PBH spin plays a significant role, and only above a critical value of the initial spin parameter $a_*$, which depends only on initial PBH mass, the graviton emission can be probed in the CMB-HD experiment. Upcoming CMB experiments such as CMB-HD and CMB-Bharat, together with future GW detectors like LISA and ET, therefore, open up an exciting possibility of constraining the PBHs parameter space and providing deeper insights into the expansion history of the universe between the end of inflation and BBN.

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N. Bhaumik, A. Ghoshal, R. Jain, et. al.
Fri, 2 Dec 22
9/81

Comments: 32 pages, 10 Figures

Synergy between CSST galaxy survey and gravitational-wave observation: Inferring the Hubble constant from dark standard sirens [CEA]

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http://arxiv.org/abs/2212.00531


Gravitational waves (GWs) from compact binary coalescences encode the absolute luminosity distances of GW sources. Once the redshifts of GW sources are known, one can use the distance-redshift relation to constrain cosmological parameters. One way to obtain the redshifts is to localize GW sources by GW observations and then use galaxy catalogs to determine redshifts from a statistical analysis of redshift information of the potential host galaxies, and such GW data are commonly referred to as dark sirens. The third-generation (3G) GW detectors are planned to work in the 2030s and will observe numerous compact binary coalescences. Using these GW events as dark sirens requires high-quality galaxy catalogs from future sky survey projects. The China Space Station Telescope (CSST) will be launched in 2024 and will observe billions of galaxies within a 17500 deg$^2$ survey area up to $z\sim 4$, providing photometric and spectroscopic galaxy catalogs. In this work, we simulate the CSST galaxy catalog and the 5-year GW data, and combine them to infer the Hubble constant ($H_0$). Our results show that the measurement precision of $H_0$ could reach better than $0.005\%$, which is an astonishing precision for the Hubble constant measurement. We conclude that the synergy between the 3G GW detectors and CSST will be of far-reaching importance in dark-siren cosmology.

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J. Song, L. Wang, Y. Li, et. al.
Fri, 2 Dec 22
11/81

Comments: 10 pages, 7 figures

Non-relativistic regime and topology II: consequences for the role of spatial curvature in cosmology [CL]

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http://arxiv.org/abs/2212.00675


In the first paper of this series, we showed that Einstein’s equation is incompatible with the non-relativistic limit in non-Euclidean topologies, i.e. for which the covering space is not $\mathbb{E}^3$. We proposed and motivated a modification of that equation such that this limit is possible. The new equation features an additional `topological term’ related to a second non-dynamical, reference, metric. In this second paper, we analyse the consequences for cosmology of this modification of Einstein’s equation. First, we show that the expansion laws do not feature anymore the curvature parameter (i.e. $\Omega = 1, \ \forall \Omega_K$). This is valid for the exact homogeneous and isotropic solution of the bi-metric theory, and for a general (inhomogeneous) solution in the non-relativistic limit. Second, we show that the weak field equations have the same number of free parameters as for the $k\Lambda$CDM model, i.e. with curvature, the differences being the disappearance of the coupling terms with that curvature in the scalar mode equations. Therefore, in our cosmological model, spatial curvature has smaller effects on the dynamics than in the $k\Lambda$CDM model; the effect remains essentially geometrical. Accordingly, the main observational difference we may expect between our model and the $k\Lambda$CDM model is a non-negligible spatial curvature inferred from cosmological data. This is particularly interesting in the context of a rising debate on the value of $\Omega_K$ and increasing observational tensions.

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Q. Vigneron
Fri, 2 Dec 22
25/81

Comments: 22 pages, 1 figure, 1 table, submitted to Classical and Quantum Gravity

Gravitational wave signatures of phase transition from hadronic to quark matter in isolated neutron stars and binaries [HEAP]

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http://arxiv.org/abs/2212.00462


The fundamental constituent of matter at high temperature and density has intrigued physicists for quite some time. Recent results from heavy-ion colliders have enriched the Quantum Chromodynamics phase diagram at high temperatures and low baryon density. However, the phase at low temperatures and finite (mostly intermediate) baryon density remain unexplored. Theoretical Quantum Chromodynamics calculation predicts phase transition from hadronic matter to quark matter at such densities. Presently, the best laboratories available to probe such densities lie at the core of neutron stars. Recent results of how such phase transition signatures can be probed using gravitational waves both in isolated neutron stars and neutron star in binaries. The isolated neutron star would probe the very low-temperature regime, whereas neutron stars in binaries would probe finite baryon density in the intermediate temperature regime. We would also discuss whether the gravitational wave signature of such phase transition is unique and the detector specification needed to detect such signals.

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R. Mallick
Fri, 2 Dec 22
37/81

Comments: 6 pages, 0 figure, contribution in ConfXIV conference

Varying alpha, blinding, and bias in existing measurements [CEA]

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http://arxiv.org/abs/2212.00791


The high resolution spectrograph ESPRESSO on the VLT allows measurements of fundamental constants at unprecedented precision and hence enables tests for spacetime variations predicted by some theories. In a series of recent papers, we developed optimal analysis procedures that both exposes and eliminates the subjectivity and bias in previous quasar absorption system measurements. In this paper we analyse the ESPRESSO spectrum of the absorption system at z_{abs}=1.15 towards the quasar HE0515-4414. Our goal here is not to provide a new unbiased measurement of fine structure constant, alpha, in this system (that will be done separately). Rather, it is to carefully examine the impact of blinding procedures applied in the recent analysis of the same data by Murphy (2022) and prior to that, in several other analyses. To do this we use supercomputer Monte Carlo AI calculations to generate a large number of independently constructed models of the absorption complex. Each model is obtained using AI-VPFIT, with alpha fixed until a “final” model is obtained, at which point alpha is then released as a free parameter for one final optimisation. The results show that the “measured” value of alpha is systematically biased towards the initially-fixed value i.e. this process produces meaningless measurements. The implication is straightforward: to avoid bias, all future measurements must include alpha as a free parameter from the beginning of the modelling process.

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C. Lee, J. Webb, R. Carswell, et. al.
Fri, 2 Dec 22
47/81

Comments: 17 pages, 7 figures, and 5 tables. Submitted to MNRAS 1 Dec 2022

Model-independent test for the cosmic distance duality relation with Pantheon and eBOSS DR16 quasar sample [CEA]

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http://arxiv.org/abs/2212.00269


In this paper, we carry out a new model-independent cosmological test for the cosmic distance duality relation~(CDDR) by combining the latest five baryon acoustic oscillations (BAO) measurements and the Pantheon type Ia supernova (SNIa) sample. Particularly, the BAO measurement from extended Baryon Oscillation Spectroscopic Survey~(eBOSS) data release~(DR) 16 quasar sample at effective redshift $z=1.48$ is used, and two methods, i.e. a compressed form of Pantheon sample and the Artificial Neural Network~(ANN) combined with the binning SNIa method, are applied to overcome the redshift-matching problem. Our results suggest that the CDDR is compatible with the observations, and the high-redshift BAO and SNIa data can effectively strengthen the constraints on the violation parameters of CDDR with the confidence interval decreasing by more than 20 percent. In addition, we find that the compressed form of observational data can provide a more rigorous constraint on the CDDR, and thus can be generalized to the applications of other actual observational data with limited sample size in the test for CDDR.

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B. Xu, Z. Wang, K. Zhang, et. al.
Fri, 2 Dec 22
48/81

Comments: 13 pages, 4 figures

Numerical simulations of inflationary dynamics: slow-roll and beyond [CL]

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http://arxiv.org/abs/2212.00529


Cosmic inflation is a period of rapid accelerated expansion of space in the very early universe. During inflation, vacuum quantum fluctuations are amplified and stretched to cosmological scales which seed the fluctuations in the cosmic microwave background as well as the large-scale structure of our universe. Large quantum fluctuations may lead to the formation of primordial black holes (PBHs) in the post-inflationary universe. Numerical simulations of the inflationary dynamics are presented here for a single canonical scalar field minimally coupled to gravity. We spell out the basic equations governing the inflationary dynamics in terms of cosmic time $t$ and define a set of dimensionless variables convenient for numerical analysis. We then provide a link to our simple numerical Python code on GitHub that can be used to simulate the background dynamics as well as the evolution of linear perturbations during inflation. The code computes both scalar and tensor power spectra for a given inflaton potential $V(\phi)$. We discuss a concrete algorithm to use the code for various purposes, especially for computing the enhanced scalar power spectrum in the context of PBH formation. We intend to extend the framework to simulate the dynamics of a number of different quantities, including the computation of scalar-induced second-order tensor power spectrum in the revised version of this manuscript in the near future.

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S. Bhatt, S. Mishra, S. Basak, et. al.
Fri, 2 Dec 22
51/81

Comments: 39 pages, 20 figures, GitHub link to codes provided in the paper, comments and suggestions are welcome

Thermodynamics of parametric dark energy models [CL]

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http://arxiv.org/abs/2212.00575


A comparative study of a set of parametric dark energy models is performed by studying the evolution of dark energy both in the past and future epochs. In addition, the age of the universe and time till the distant future $(a=1000)$ are estimated. The validity of generalized second law of thermodynamic in different parametric models is also ascertained.

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S. Rath
Fri, 2 Dec 22
54/81

Comments: N/A

Realization of Dirac quantization in loop quantum gravity [CL]

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http://arxiv.org/abs/2212.00203


The system of gravity coupled to the non-rotational dust field is studied at both classical and quantum levels. The scalar constraint of the system can be written in the form of a true physical Hamiltonian with respect to the dust time. In the framework of loop quantum gravity, the scalar constraint is promoted to a well-defined operator in a suitable Hilbert space of the coupled system, such that the physical Hamiltonian becomes a symmetric operator. By the deparametrized form, a general expression of the solutions to the quantum scalar constraint is obtained, and the observables on the space of solutions can be constructed. Moreover, the Dirac quantization procedure can be fully carried out in loop quantum gravity by this system.

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X. Zhang and Y. Ma
Fri, 2 Dec 22
59/81

Comments: 6 pages

Using Gray Sirens to Resolve the Hubble-Lemaître Tension [CL]

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http://arxiv.org/abs/2212.00163


The measurement of the Hubble-Lema\^{i}tre constant $(H_0)$ from the cosmic microwave background and the Type IA supernovae are at odds with each other. One way to resolve this tension is to use an independent way to measure $H_0$. This can be accomplished by using gravitational-wave (GW) observations. Previous works have shown that with the onset of the next-generation of GW detector networks, it will be possible to constrain $H_0$ better than $2\%$ (which is enough to resolve the tension) with binary black hole systems, also called dark sirens. Bright sirens like binary neutron star systems can also help resolve the tension if both the GW and the following electromagnetic counterpart are detected. In this work, we assess the potential of using neutron star-black hole (NSBH) mergers to measure the Hubble-Lema\^{i}tre constant, both as dark sirens as well as bright sirens, thus, assigning them the term gray sirens. We find that the Voyager network might be able to resolve the tension using NSBH mergers in an observation span of 5 years, whereas next-generation networks which include the Cosmic Explorer detectors and the Einstein Telescope will be able to measure the $H_0$ to sub-percent level.

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I. Gupta
Fri, 2 Dec 22
65/81

Comments: 22 pages, 10 figures, 9 tables

Collinear and triangular solutions to the three-body problem in the parameterized post-Newtonian formalism [CL]

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http://arxiv.org/abs/2212.00198


This paper investigates the three-body problem in the parameterized post-Newtonian (PPN) formalism, for which we focus on a coplanar case in a class of fully conservative theories characterized by the Eddington-Robertson parameters $\beta$ and $\gamma$. It is shown that there can still exist a collinear equilibrium configuration and a triangular one, each of which is a generalization of the post-Newtonian equilibrium configuration in general relativity. The collinear configuration can exist for arbitrary mass ratio, $\beta$, and $\gamma$. On the other hand, the PPN triangular configuration depends on the nonlinearity parameter $\beta$ but not on $\gamma$. For any value of $\beta$, the equilateral configuration is possible, if and only if three finite masses are equal or two test masses orbit around one finite mass. For general mass cases, the PPN triangle is not equilateral as in the post-Newtonian case. It is shown also that the PPN displacements from the standard Lagrange points $L_1$, $L_2$ and $L_3$ depend on $\beta$ and $\gamma$, whereas those to $L_4$ and $L_5$ rely only on $\beta$.

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Y. Nakamura and H. Asada
Fri, 2 Dec 22
79/81

Comments: 8 pages, 2 figures

Probing Ensemble Properties of Vortex-avalanche Pulsar Glitches with a Stochastic Gravitational-Wave Background Search [CL]

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http://arxiv.org/abs/2211.16857


A stochastic gravitational-wave background (SGWB) is expected to be produced by the superposition of individually undetectable, unresolved gravitational-wave (GW) signals from cosmological and astrophysical sources. Such a signal can be searched with dedicated techniques using the data acquired by a network of ground-based GW detectors. In this work, we consider the astrophysical SGWB resulting from pulsar glitches, which are sudden increases in the rotational pulsar frequency, within our Galaxy. More specifically, we assume glitches to be associated with quantized, superfluid, vortex-avalanches in the pulsars, and we model the SGWB from the superposition of GW bursts emitted during the glitching phase. We perform a cross-correlation search for this SGWB-like signal employing the data from the first three observation runs of Advanced LIGO and Virgo. Not having found any evidence for a SGWB signal, we set upper limits on the dimensionless energy density parameter $\Omega_{\mathrm{gw}}(f)$ for two different power-law SGWBs, corresponding to two different glitch regimes. We obtain $\Omega_{\mathrm{gw}}(f)\leq 7.5 \times 10^{-10}$ at 25 Hz for a spectral index 5/2, and $\Omega_{\mathrm{gw}}(f)\leq 5.7 \times 10^{-17}$ at 25 Hz for a spectral index 17/2. We then use these results to set constraints on the average glitch duration and the average radial motion of the vortices during the glitches for the population of the glitching Galactic pulsars, as a function of the Galactic glitch rate.

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F. Lillo, J. Suresh, A. Depasse, et. al.
Thu, 1 Dec 22
3/85

Comments: 13 pages, 3 figures, 1 table

Large-scale geometry of the Universe [CEA]

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http://arxiv.org/abs/2211.16893


The large scale geometry of the late Universe can be decomposed as R$\times {\Sigma}_3$, where R stands for cosmic time and ${\Sigma}_3$ is the three dimensional spatial manifold. We conjecture that the spatial geometry of the Universe’s spatial section ${\Sigma}_3$ conforms with the Thurston-Perelman theorem, according to which the geometry of $\Sigma_3$ is either one of the eight geometries from the Thurston geometrization conjecture, or a combination of Thurston geometries smoothly sewn together. We assume that topology of individual geometries plays no observational role, i.e. the size of individual geometries is much larger than the Hubble radius today. We investigate the dynamics of each of the individual geometries by making use of the simplifying assumption that our local Hubble patch consists of only one such geometry, which is approximately homogeneous on very large scales, but spatial isotropy is generally violated. Spatial anisotropies grow in time in decelerating universes, but they decay in accelerating universes. The thus-created anisotropy problem can be solved by a period of primordial inflation, akin to how the flatness problem is solved. Therefore, as regards Universe’s large scale geometry, any of the Thurston’s geometries should be considered on a par with Friedmann’s geometries. We consider two observational methods that can be used to test our conjecture: one based on luminosity distance and one on angular diameter distance measurements, but leave for the future their detailed forecasting implementations.

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Y. Awwad and T. Prokopec
Thu, 1 Dec 22
4/85

Comments: 38 pages, 36 figures

Observational constraints on Tsallis holographic dark energy with Ricci horizon cutoff [CL]

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http://arxiv.org/abs/2211.17212


In this research, we are interested in constraining the nonlinear interacting and noninteracting Tsallis holographic dark energy (THDE) with Ricci horizon cutoff by employing three observational datasets. To this aim, the THDE with Ricci horizon considering the noninteraction and nonlinear interaction terms will be fitted by the SNe Ia, SNe Ia+H(z), and SNe Ia+H(z)+GRB samples to investigate the Hubble ($H(z)$), dark energy equation of state ($\omega_{DE}$), effective equation of state ($\omega_{eff}$), and deceleration ($q$) parameters. Investigating the $H(z)$ parameter illustrates that our models are in good consistent with respect to observation. Also, it can reveal the turning point for both noninteracting and nonlinear interacting THDE with Ricci cutoff in the late time era. Next, the analysis of the $\omega_{DE}$ for our models displays that the dark energy can experience the phantom state at the current time. However, it lies in the quintessence regime in the early era and approaches the cosmological constant in the late-time epoch. Similar results will be for the $\omega_{eff}$ parameter with this difference that the $\omega_{eff}$ will experience the quintessence region at the current redshift. Next to the mentioned parameters, the study of the $q$ parameter indicates that the models satisfy an acceptable transition phase from the matter to the dark energy-dominated era. After that, the classical stability ($v_{s}^{2}$) will be analyzed for our models. The $v_{s}^{2}$ shows that the noninteracting and nonlinear interacting THDE with Ricci cutoff will be stable in the past era, unstable in the present, and progressive epochs. Then, we will employ the $Jerk$ ($J$) and $OM$ parameters to distinguish between our models and the $\Lambda CDM$ model. Finally, we will calculate the age of the Universe for the THDE and nonlinear interacting THDE with Ricci as the IR cutoff.

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Z. Mangoudehi
Thu, 1 Dec 22
9/85

Comments: 35 pages. The manuscript number is ASTR-D-22-00103R3

A cosmographic outlook on dark energy and modified gravity [CEA]

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http://arxiv.org/abs/2211.17194


The cosmographic technique is a powerful model-independent tool for distinguishing between competing cosmological scenarios. The key strengths and weaknesses of standard cosmography are discussed in view of healing the convergence problem endangering the high-redshift expansions of cosmological distances. We focus especially on rational cosmographic approximations to reconstruct the dark energy behaviour under the $f(R)$, $f(T)$ and $f(Q)$ gravity frameworks. Based on observational constraints over the cosmographic series, we investigate the origin of cosmic acceleration and the possibility of going beyond the standard cosmological model to explain the dark energy problem.

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S. Capozziello and R. D’Agostino
Thu, 1 Dec 22
20/85

Comments: 16 pages, 5 figures. Proceeding of XVIII Vulcano Workshop on Frontier Objects in Astrophysics and Particle Physics, to appear in Frascati Physics Series 2023

Quantum Initial Conditions for Curved Inflating Universes [CL]

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http://arxiv.org/abs/2211.17248


We discuss the challenges of motivating, constructing, and quantising a canonically-normalised inflationary perturbation in spatially curved universes. We show that this has historically proved challenging due to the interaction of non-adiabaticity with spatial curvature. We propose a novel curvature perturbation which is canonically normalised, unique up to a single scalar parameter. This corrected quantisation has potentially observational consequences via modifications to the primordial power spectrum at large angular scales, as well as theoretical implications for quantisation procedures in curved cosmologies filled with a scalar field.

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M. Letey, Z. Shumaylov, F. Agocs, et. al.
Thu, 1 Dec 22
27/85

Comments: 13 pages, 3 figures; v1

$f(R)$ gravity in the Jordan Frame as a Paradigm for the Hubble Tension [CL]

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http://arxiv.org/abs/2211.16737


We analyze the $f(R)$ gravity in the so-called Jordan frame, as implemented to the isotropic Universe dynamics. The goal of the present study is to show that, according to recent data analyses of the supernovae Ia Pantheon sample, it is possible to account for an effective redshift-dependence of the Hubble constant via the dynamics of a non-minimally coupled scalar field, emerging in the $f(R)$ gravity. We face the question both from an analytical and purely numerical point of view, following the same technical paradigm. We arrive to establish that the expected decay of the Hubble constant with the redshift $z$ is ensured by a form of the scalar field potential, which remains essentially constant for $z\lesssim0.3$, independently if this request is made a priori, as in the analytical approach, or obtained a posteriori, when the numerical procedure is addressed. Thus, we demonstrate that an $f(R)$ dark energy model is able to account for an apparent variation of the Hubble constant due to the rescaling of the Einstein constant by the $f(R)$ scalar mode.

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T. Schiavone and G. Montani
Thu, 1 Dec 22
38/85

Comments: 5 pages, 2 figures, to be submitted to MNRAS Letter

Probing new physics on the horizon of black holes with gravitational waves [CL]

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http://arxiv.org/abs/2211.16900


Black holes are the most compact objects in the Universe. According to general relativity, black holes have a horizon that hides a singularity where Einstein’s theory breaks down. Recently, gravitational waves opened the possibility to probe the existence of horizons and investigate the nature of compact objects. This is of particular interest given some quantum-gravity models which predict the presence of horizonless and singularity-free compact objects. Such exotic compact objects can emit a different gravitational-wave signal relative to the black hole case. In this thesis, we analyze the stability of horizonless compact objects, and derive a generic framework to compute their characteristic oscillation frequencies. We provide an analytical, physically-motivated template to search for the gravitational-wave echoes emitted by these objects in the late-time postmerger signal. Finally, we infer how extreme mass-ratio inspirals observable by future gravitational-wave detectors will allow for model-independent tests of the black hole paradigm.

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E. Maggio
Thu, 1 Dec 22
45/85

Comments: PhD thesis, 160 pages

The one-loop bispectrum of galaxies in redshift space from the Effective Field Theory of Large-Scale Structure [CEA]

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http://arxiv.org/abs/2211.17130


We derive the kernels and the Effective Field Theory of Large-Scale Structure counterterms for the one-loop bispectrum of dark matter and of biased tracers in real and redshift space. This requires the expansion of biased tracers up to fourth order in fluctuations. In the process, we encounter several subtleties related to renormalization. One is the fact that, in renormalizing the momentum, a local counterterm contributes non-locally. A second subtlety is related to the renormalization of local products of the velocity fields, which need to be expressed in terms of the renormalized velocity in order to preserve Galilean symmetry. We check that the counterterms we identify are necessary and sufficient to renormalize the one-loop bispectrum at leading and subleading order in the derivative expansion. The kernels that we originally present here have already been used for the first analyses of the one-loop bispectrum in BOSS data [1, 2].

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G. D’Amico, Y. Donath, M. Lewandowski, et. al.
Thu, 1 Dec 22
47/85

Comments: 39 + 27 pages, ancillary Mathematica file in “Other formats”

The effect of quantum fluctuations in compact star observables [CL]

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http://arxiv.org/abs/1710.05410


Astrophysical measurements regarding compact stars are just ahead of a big evolution jump, since the NICER experiment deployed on ISS on 14 June 2017. This will soon provide data that would enable the determination of compact star radius with less than 10% error. This poses new challenges for nuclear models aiming to explain the structure of super dense nuclear matter found in neutron stars.
Detailed studies of the QCD phase diagram shows the importance of bosonic quantum fluctuations in the cold dense matter equation of state. Here, we using a demonstrative model to show the effect of bosonic quantum fluctuations on compact star observables such as mass, radius, and compactness. We have also calculated the difference in the value of compressibility which is caused by quantum fluctuations.
The above mentioned quantities are calculated in mean field, one-loop and in high order many-loop approximation. The results show that the magnitude of these effects is ~5%, which place it into the region where forthcoming high-accuracy measurements may detect it.

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P. Pósfay, G. Barnaföldi and A. Jakovác
Thu, 1 Dec 22
59/85

Comments: 6 pages 4 figues, minor corrections were added

Centenary of Alexander Friedmann's Prediction of the Universe Expansion and the Quantum Vacuum [CL]

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http://arxiv.org/abs/2211.17101


We review the main scientific pictures of the universe developed from ancient times to Albert Einstein and underline that all of them treated the universe as a stationary system with unchanged physical properties. In contrast to this, 100 years ago Alexander Friedmann predicted that the universe expands starting from the point of infinitely large energy density. We briefly discuss the physical meaning of this prediction and its experimental confirmation consisting of the discovery of redshift in the spectra of remote galaxies and relic radiation. After mentioning the horizon problem in the theory of the hot universe, the inflationary model is considered in connection with the concept of quantum vacuum as an alternative to the inflaton field. The accelerated expansion of the universe is discussed as powered by the cosmological constant originating from the quantum vacuum. The conclusion is made that since Alexander Friedmann’s prediction of the universe expansion radically altered our picture of the world in comparison with the previous epochs, his name should be put on a par with the names of Ptolemy and Copernicus.

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G. Klimchitskaya and V. Mostepanenko
Thu, 1 Dec 22
63/85

Comments: 16 pages, 1 figure

Islands in the Fluid: Islands are Common in Cosmology [CL]

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http://arxiv.org/abs/2211.16600


We discuss the possibility of entanglement islands in cosmological spacetimes with a general perfect fluid with an equation of state $w$. We find that flat universes with time-symmetric slices where the Hubble parameter vanishes always have islands on that slice. We then move away from such slices, considering still universes with a general perfect fluid. Under the local thermal equilibrium assumption, the comoving entropy density $s_c$ is constant. As a result, the conditions for an island become an inequality between the energy density (or Hubble parameter) and the temperature at some time of normalization. The consequences are that islands can exist for practically all fluids that are not radiation, i.e. $w\neq 1/3$. We also discuss the ramifications of our results for universes with spatial curvature. Finally, we show that islands occur in the Simple Harmonic Universe model which has no classical singularity at the background level, in contrast to all previous examples where islands occurred only in space-times with singularities.

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I. Ben-Dayan, M. Hadad and E. Wildenhain
Thu, 1 Dec 22
81/85

Comments: 26 pages, 5 figures

Freezing-In Gravitational Waves [CL]

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http://arxiv.org/abs/2211.16513


The thermal plasma in the early universe produced a stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). In previous works only single graviton production processes that contribute to the CGMB have been considered. Here we also investigate graviton pair production processes and show that these can lead to a significant contribution if the maximum temperature of the universe in units of Planck mass divided by the internal coupling in the heat bath is large enough. As the dark matter freeze-in production mechanism is conceptually very similar to the GW production mechanism from the primordial thermal plasma, we refer to the latter as “GW freeze-in production”. We also show that quantum gravity effects arising in single graviton production are smaller than the leading order result by a factor of the square of the ratio between the maximum temperature and the Planck mass. In our work we explicitly compute the CGMB spectrum within a scalar model with quartic interaction.

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J. Ghiglieri, J. Schütte-Engel and E. Speranza
Thu, 1 Dec 22
82/85

Comments: 18 pages, 6 figures

The Hubble tension from the standpoint of quantum cosmology [CL]

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http://arxiv.org/abs/2211.16394


The Hubble tension is analyzed in the framework of quantum cosmological approach. It is found that there arises a new summand in the expression for the total energy density stipulated by the quantum Bohm potential. This additional energy density modifies the expansion history of the early universe and decays faster than radiation in late universe. Similarly to physical models with early dark energy, taking account of this matter source of quantum nature can, in principle, eliminate a discrepancy between the Hubble constant estimates obtained in different approaches. The model been considered allows one to extend the standard cosmology to quantum sector.

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V. Kuzmichev and V. Kuzmichev
Wed, 30 Nov 22
53/81

Comments: 6 pages

Bayesian modelling of scattered light in the LIGO interferometers [IMA]

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http://arxiv.org/abs/2211.15867


Excess noise from scattered light poses a persistent challenge in the analysis of data from gravitational wave detectors such as LIGO. We integrate a physically motivated model for the behavior of these “glitches” into a standard Bayesian analysis pipeline used in gravitational wave science. This allows for the inference of the free parameters in this model, and subtraction of these models to produce glitch-free versions of the data. We show that this inference is an effective discriminator of the presence of the features of these glitches, even when those features may not be discernible in standard visualizations of the data.

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R. Udall and D. Davis
Wed, 30 Nov 22
66/81

Comments: This article has been submitted to Applied Physics Letters

Four hints and test candidates of the local cosmic expansion [CL]

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http://arxiv.org/abs/2211.15668


The expansion of the universe on short distance scales is a new frontier to investigate the dark energy. The excess orbital decay in binary pulsars may be related to acceleration by the local cosmic expansion, called the cosmic drag. Modern observations of two independent binaries (PSR B1534+12 and PSR B1913+16) support this interpretation and result in a scale-independent expansion with viscous uniformity, in which binary systems have a smaller expansion rate than the Hubble constant. This paper shows additional evidential binaries (PSR J1012-5307 and PSR J1906+0746), supporting the cosmic drag picture. The total anomaly of the conventional model is about $3.6\,\sigma$ including two evidential binaries reported before. In addition, an observable range of the cosmic drag has been calculated for typical models of both NS-NS binary and NS-WD binary. In this region, six test candidates are listed with predictions of the excess orbital decay.

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K. Agatsuma
Wed, 30 Nov 22
70/81

Comments: 5 pages, 1 figure

Spin-2 dark matter from anisotropic Universe in bigravity [CL]

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http://arxiv.org/abs/2211.15873


Bigravity is one of the natural extensions of general relativity and contains an additional massive spin-2 field which can be a good candidate for dark matter. To discuss the production of spin-2 dark matter, we study fixed point solutions of the background equations for axisymmetric Bianchi type-I Universes in two bigravity theories without Boulware-Deser ghost, i.e., Hassan-Rosen bigravity and Minimal Theory of Bigravity. We investigate the local and global stability of the fixed points and classify them. Based on the general analysis, we propose a new scenario where spin-2 dark matter is produced by the transition from an anisotropic fixed point solution to isotropic one. The produced spin-2 dark matter can account for all or a part of dark matter and can be directly detected by laser interferometers in the same way as gravitational waves.

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Y. Manita, K. Aoki, T. Fujita, et. al.
Wed, 30 Nov 22
73/81

Comments: 15 pages, 3 figures

Primordial Black Hole Formation during a Strongly Coupled Crossover [CEA]

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http://arxiv.org/abs/2211.15674


The final mass distribution of primordial black holes is sensitive to the equation of state of the Universe at the scales accessible by the power spectrum. Motivated by the presence of phase transitions in several beyond the Standard Model theories, some of which are strongly coupled, we analyse the production of primordial black holes during such phase transitions, which we model using the gauge/gravity duality. We focus in the (often regarded as physically uninteresting) case for which the phase transition is just a smooth crossover. We find an enhancement of primordial black hole production in the range $M_{\rm{PBH}}\in[10^{-16},10^{-6}]M_{\odot}$.

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A. Escrivà and J. Subils
Wed, 30 Nov 22
75/81

Comments: 5 pages + references, 4 figures

FeynMG: a FeynRules extension for scalar-tensor theories of gravity [CL]

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http://arxiv.org/abs/2211.14300


The ability to represent perturbative expansions of interacting quantum field theories in terms of simple diagrammatic rules has revolutionized calculations in particle physics (and elsewhere). Moreover, these rules are readily automated, a process that has catalysed the rise of symbolic algebra packages. However, in the case of extended theories of gravity, such as scalar-tensor theories, it is necessary to precondition the Lagrangian to apply this automation or, at the very least, to take advantage of existing software pipelines. We present a Mathematica code FeynMG, which works in conjunction with the well-known package FeynRules, to do just that: FeynMG takes as inputs the FeynRules model file for a non-gravitational theory and a user-supplied gravitational Lagrangian. FeynMG provides functionality that inserts the minimal gravitational couplings of the degrees of freedom specified in the model file, determines the couplings of the additional tensor and scalar degrees of freedom (the metric and the scalar field from the gravitational sector), and preconditions the resulting Lagrangian so that it can be passed to FeynRules, either directly or by outputting an updated FeynRules model file. The Feynman rules can then be determined and output through FeynRules, using existing universal output formats and interfaces to other analysis packages.

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S. Muñoz, E. Copeland, P. Millington, et. al.
Tue, 29 Nov 22
9/80

Comments: 35 pages, 1 figure, GitLab link: this https URL

Impacts of the external environment on the Virgo detector during the third Observing Run [CL]

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http://arxiv.org/abs/2211.14947


Sources of geophysical noise (such as wind, sea waves and earthquakes) or of anthropogenic noise (nearby activities, road traffic, etc.) impact ground-based gravitational-wave (GW) interferometric detectors, causing transient sensitivity worsening and gaps in data taking. During the one year-long third Observing Run (O3: from April 01, 2019 to March 27, 2020), the Virgo Collaboration collected a large dataset, which has been used to study the response of the Advanced Virgo detector to a variety of environmental conditions. We correlated environmental parameters to global detector performance, such as observation range (the live distance up to which a given GW source could be detected), duty cycle and control losses (losses of the global working point, the instrument configuration needed to observe the cosmos). Where possible, we identified weaknesses in the detector that will be used to elaborate strategies in order to improve Virgo robustness against external disturbances for the next data taking period, O4, currently planned to start in March 2023. The lessons learned could also provide useful insights for the design of the next generation of ground-based interferometers.

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N. Arnaud
Tue, 29 Nov 22
11/80

Comments: Contribution to the Proceedings of the 41st International Conference on High Energy Physics – ICHEP2022. On behalf of the Virgo Collaboration

Constraining Single-Field Inflation with MegaMapper [CEA]

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http://arxiv.org/abs/2211.14899


We forecast the constraints on single-field inflation from the bispectrum of future high-redshift surveys such as MegaMapper. Considering non-local primordial non-Gaussianity (NLPNG), we find that current methods will yield constraints of order $\sigma(f_{\rm NL}^{\rm eq})\approx 23$, $\sigma(f_{\rm NL}^{\rm orth})\approx 12$ in a joint power-spectrum and bispectrum analysis, varying both nuisance parameters and cosmology, including a conservative range of scales. Fixing cosmological parameters and quadratic bias parameter relations, the limits tighten significantly to $\sigma(f_{\rm NL}^{\rm eq})\approx 17$, $\sigma(f_{\rm NL}^{\rm orth})\approx 8$. These compare favorably with the forecasted bounds from CMB-S4: $\sigma(f_{\rm NL}^{\rm eq})\approx 21$, $\sigma(f_{\rm NL}^{\rm orth})\approx 9$, with a combined constraint of $\sigma(f_{\rm NL}^{\rm eq})\approx 14$, $\sigma(f_{\rm NL}^{\rm orth})\approx 7$; this weakens only slightly if one instead combines with data from the Simons Observatory. We additionally perform a range of Fisher analyses for the error, forecasting the dependence on nuisance parameter marginalization, scale cuts, and survey strategy. Lack of knowledge of bias and counterterm parameters is found to significantly limit the information content; this could be ameliorated by tight simulation-based priors on the nuisance parameters. The error-bars decrease significantly as the number of observed galaxies and survey depth is increased: as expected, deep dense surveys are the most constraining, though it will be difficult to reach $\sigma(f_{\rm NL})\approx 1$ with current methods. The NLPNG constraints will tighten further with improved theoretical models (incorporating higher-loop corrections), as well as the inclusion of additional higher-order statistics.

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G. Cabass, M. Ivanov, O. Philcox, et. al.
Tue, 29 Nov 22
26/80

Comments: 6 pages, 3 figures, submitted to Phys. Lett. B

Completely Dark Matter from Rapid-Turn Multifield Inflation [CL]

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http://arxiv.org/abs/2211.14323


We study cosmological gravitational particle production as applied to “rapid-turn” models of inflation involving two scalar fields. We are interested in the production of massive spin-0 particles that only interact gravitationally and provide a candidate for the dark matter. Specifically, we study two models of rapid-turn multifield inflation, motivated in part by the de Sitter swampland conjecture, that are distinguished by the curvature of field space and the presence or absence of field space ‘angular momentum’ conservation. We find that one of these models leads to insufficient particle production and cannot explain the observed dark matter relic abundance. The second model is able to explain the origin of spin-0 dark matter via gravitational production, and we identify the relevant region of parameter space that is consistent with measurements of the dark-matter relic abundance, the dark-matter-photon isocurvature perturbations, and the spectrum of curvature perturbations that is probed by cosmological observations. Our work demonstrates the compatibility of the de Sitter swampland conjecture with completely dark matter.

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E. Kolb, A. Long, E. McDonough, et. al.
Tue, 29 Nov 22
27/80

Comments: N/A

Gravitational-wave cosmology with dark sirens: state of the art and perspectives for 3G detectors [CL]

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http://arxiv.org/abs/2211.15512


A joint fit of the mass and redshift distributions of the population of Binary Black Holes detected with Gravitational-Wave observations can be used to obtain constraints on the Hubble parameter and on deviations from General Relativity in the propagation of Gravitational Waves. We first present applications of this technique to the latest catalog of Gravitational-Wave events, focusing on the comparison of different parametrizations for the source-frame mass distribution of Black Hole Binaries. We find that models with more than one feature are favourite by the data, as suggested by population studies, even when varying the cosmology. Then, we discuss perspectives for the use of this technique with third generation Gravitational-Wave detectors, exploiting the recently developed Fisher information matrix Python code GWFAST.

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M. Mancarella, N. Borghi, S. Foffa, et. al.
Tue, 29 Nov 22
39/80

Comments: 5 pages, 2 figures, Contribution to the ICHEP 2022 conference proceedings

Implications of the Weak Gravity Conjecture for Tidal Love Numbers of Black Holes [CL]

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http://arxiv.org/abs/2211.14325


The Weak Gravity Conjecture indicates that extremal black holes in the low energy effective field theory should be able to decay. This criterion gives rise to non-trivial constraints on the coefficients of higher-order derivative corrections to gravity. In this paper, we investigate the tidal deformability of neutral black holes due to higher-order derivative corrections. As a case in point, we consider a correction of cubic order in the Riemann curvature tensor. The tidal Love numbers of neutral black holes receive leading-order corrections from higher-order derivative terms, since black holes in pure General Relativity have vanishing tidal Love number. We conclude that the tidal deformability of neutral black holes is constrained by the Weak Gravity Conjecture, and therefore provides a test for quantum gravity.

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V. Luca, J. Khoury and S. Wong
Tue, 29 Nov 22
41/80

Comments: 21 pages, 2 figures

Primordial black holes and gravitational waves from non-canonical inflation [CEA]

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http://arxiv.org/abs/2211.14900


Primordial black holes (PBHs) can generically form in inflationary setups through the collapse of enhanced cosmological perturbations, providing us access to the early Universe through their associated observational signatures. In the current work we propose a new mechanism of PBH production within non-canonical inflation, using a class of steep-deformed inflationary potentials compatible with natural values for the non-canonical exponents. In particular, by requiring significant PBH production we extract constraints on the non-canonical exponents. Additionally, we find that our scenario can lead to the formation of asteroid-mass PBHs, which can account for the totality of the dark matter, as well as to production of solar-mass PBHs within the LIGO/VIRGO detection band. Finally, we find that the enhanced cosmological perturbations which collapse to form PBHs can produce a stochastic gravitational-wave (GW) background induced by second-order gravitational interactions. Very interestingly, we obtain a GW signal detectable by future GW experiments, in particular by SKA, LISA and BBO.

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T. Papanikolaou, A. Lymperis, S. Lola, et. al.
Tue, 29 Nov 22
56/80

Comments: 17 pages without appendices (23 in total), 7 figures

Palatini formulation for gauge theory: implications for slow-roll inflation [CEA]

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http://arxiv.org/abs/2211.15584


We consider a formulation of gauge field theory where the gauge field $A_\alpha$ and the field strength $F_{\alpha\beta}$ are independent variables, as in the Palatini formulation of gravity. For the simplest gauge field action, this is known to be equivalent to the usual formulation. We add non-minimal couplings between $F_{\alpha\beta}$ and a scalar field, solve for $F_{\alpha\beta}$ and insert it back into the action. This leads to modified gauge field and scalar field terms. We consider slow-roll inflation and show that because of the modifications to the scalar sector, adding higher order terms to the inflaton potential does not spoil its flatness, unlike in the usual case. Instead they make the effective potential closer to quadratic. The modifications also solve the problem that Higgs inflation in the Palatini formulation is sensitive to higher order terms.

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S. Rasanen and Y. Verbin
Tue, 29 Nov 22
60/80

Comments: 6+2 pages, no figures