General Relativity and Quantum Cosmology
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 [1] arXiv:2406.12933 [pdf, html, other]

Title: Charged Quark Stars and Extreme Compact Objects in Regularized 4D EinsteinGaussBonnet GravityComments: arXiv admin note: substantial text overlap with arXiv:2309.00703Subjects: General Relativity and Quantum Cosmology (grqc); High Energy Astrophysical Phenomena (astroph.HE)
Since the derivation of a welldefined $D\rightarrow 4$ limit for 4 dimensional Einstein GaussBonnet (4DEGB) gravity coupled to a scalar field, there has been interest in testing it as an alternative to Einstein's general theory of relativity. Using the TolmanOppenheimerVolkoff (TOV) equations modified for charge and 4DEGB gravity, we model the stellar structure of charged, noninteracting quark stars. We find that increasing the GaussBonnet coupling constant $\alpha$ or the charge $Q$ both tend to increase the massradius profiles of quark stars described by this theory, allowing a given central pressure to support larger quark stars in general. We also derive a generalization of the Buchdahl bound for charged stars in 4DEGB gravity. As in the uncharged case, we find that quark stars can exist below the general relativistic Buchdahl bound (BB) and Schwarzschild radius $R=2M$, due to the lack of a mass gap between black holes and compact stars in the 4DEGB theory. Even for $\alpha$ well within current observational constraints, we find that quark star solutions in this theory can describe Extreme Compact Charged Objects (ECCOs), objects whose radii are smaller than what is allowed by general relativity.
 [2] arXiv:2406.13020 [pdf, html, other]

Title: Microscale torsion resonators for shortrange gravity experimentsSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph); Instrumentation and Detectors (physics.insdet)
Measuring gravitational interactions on sub100$\mu$m length scales offers a window into physics beyond the Standard Model. However, shortrange gravity experiments are limited by the ability to position sufficiently massive objects to within small separation distances. Here we propose massloaded silicon nitride ribbons as a platform for testing the gravitational inverse square law at separations currently inaccessible with traditional torsion balances. These microscale torsion resonators benefit from low thermal noise due to straininduced dissipation dilution while maintaining compact size (<100$\,\mu$g) to allow close approach. Considering an experiment combining a 40$\,\mu$g torsion resonator with a source mass of comparable size (130$\,\mu$g) at separations down to 25$\,\mu$m, and including limits from thermomechanical noise and systematic uncertainty, we predict these devices can set novel constraints on Yukawa interactions within the 1100$\,\mu$m range.
 [3] arXiv:2406.13032 [pdf, html, other]

Title: Compact regular objects from an electrified Tolmanlike density: A new interior region for the KerrNewman spacetimeSubjects: General Relativity and Quantum Cosmology (grqc)
Charged static and rotating objects as solutions of the EinsteinMaxwell field equations are obtained and studied in the present work. The full spacetime geometry is obtained by matching two spacetime regions, an interior region containing electrified matter and an exterior electrovacuum region. In the static case, the interior region contains a spherically symmetric distribution of matter constituted by a de Sittertype perfect fluid with electric charge, whose energy density profile is given by a Tolmanlike relation. The interior solution is smoothly matched with the exterior ReissnerNordström electrovacuum solution, thus producing different kinds of objects, such as charged regular black holes and overcharged tension stars, that we analyze in detail. We also investigate the connection between the present static solution and the regular black holes with a de Sitter core presented in the work by Lemos and Zanchin [Phys. Rev. D 83, 124005 (2011)]. We then employ the GürsesGürsey metric and apply the NewmanJanis algorithm to construct a charged rotating interior geometry from the static interior solution. The resulting interior metric and the electromagnetic field are smoothly matched to the exterior KerrNewman electrovacuum solution, thus producing a regular interior for the exterior KerrNewman geometry. The main properties of the complete rotating solution are analyzed in detail, showing that different kinds of rotating objects, such as charged rotating black holes and other charged rotating objects, also emerge in this solution.
 [4] arXiv:2406.13068 [pdf, html, other]

Title: A new energy inequality in AdSComments: 13 pages, 3 figsSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
We study time symmetric initial data for asymptotically AdS spacetimes with conformal boundary containing a spatial circle. Such $d$dimensional initial data sets can contain $(d2)$dimensional minimal surfaces if the circle is contractible. We compute the minimum energy of a large class of such initial data as a function of the area $A$ of this minimal surface. The statement $E \ge E_{min}(A)$ is analogous to the Penrose inequality which bounds the energy from below by a function of the area of a $(d1)$dimensional minimal surface.
 [5] arXiv:2406.13082 [pdf, other]

Title: The HanburyBrown and Twiss effect in inflationary cosmological perturbationsSubjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
The simplest model of inflation is based around an inflaton field that starts in a coherent false vacuum state with a positive cosmological constant, rolls slowly to the true vacuum and relaxes to it via reheating. We examine whether the scale of the transition from coherence to chaoticity can be examined via the HanburyBrown and Twiss (HBT) effect, in parallel with analogous problems of heavy ion physics (the ``pion laser'' and the thermalizing glasma).
We develop an ansatz which contains a definition of ''chaoticity'' which parallels that of the usual setups where HBT is used.
However, we also discuss the differences between the inflationary setup and more mainstream uses of HBT and conclude that these are more significant than the similarities, making the use of the developed methodology uncertain.  [6] arXiv:2406.13132 [pdf, html, other]

Title: Cosmic slowing down of acceleration with the ChaplyginJacobi gas as a dark fluidComments: 16 pages, 5 figuresSubjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO)
A particular generalization of the Chaplygin inflationary model, using the formalism of HamiltonJacobi and elliptic functions, results in a more general nonlinear Chaplygintype equation of state (ChaplyginJacobi model). We investigate the implementation of this model as a dark energy (DE) fluid to explain the recent acceleration of the universe. Unlike $\Lambda$CDM and other Chaplyginlike fluids, where the final fate of the universe is an eternal de Sitter (dS) phase, the dynamics of this model allow for the possibility of a decelerating phase in the future, following the current accelerating phase. In other words, a transient acceleration arises, accounting for the recently claimed slowing down phenomenon. This ChaplyginJacobi model shows important differences compared to the standard and generalized Chaplygin gas models. Additionally, we perform a Markov Chain Monte Carlo (MCMC) analysis using several datasets, including Type Ia Supernovae (SnIa), Cosmic Chronometers (CC), and Fast Radio Bursts (FRBs), to examine the observational viability of the model. Our results indicate that a transient phase of accelerated expansion is not excluded by current observations.
 [7] arXiv:2406.13189 [pdf, html, other]

Title: The cosmological significance of boundary term in nonmetricity gravitySubjects: General Relativity and Quantum Cosmology (grqc)
Within the context of metricaffine gravity, we examine the significance of the boundary term in symmetric teleparallel gravity by employing the cosmological dynamical system analysis method. We focus on the novel gravity models characterized by the functions $f(Q,C)$, where $f$ is a smooth function of the nonmetricity scalar $Q$ and the associated boundary term $C$. In a cosmological setting adopting three different classes of symmetric teleparallel affine connections, we investigate a model $f(Q,C)=Q^{s}+eC^{r}$, and some special cases of this model. We show that the boundary term which is added to the Einsteinian field equations (or equivalently to $f(Q)=Q$ ones) are capable of bringing forward solutions corresponding to the early accelerated expansion. This alludes the physics behind the boundary terms which usually are discarded in the most gravitational theories.
 [8] arXiv:2406.13224 [pdf, html, other]

Title: Possibility of the Traversable Wormholes in the Galactic Halos within $4D$ EinsteinGaussBonnet GravityComments: Annalen der Physik published versionJournalref: Annalen der Physik, 536 (2024) 2400114Subjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
Recently, there has been significant interest regarding the regularization of a $D\rightarrow 4$ limit of EinsteinGaussBonnet (EGB) gravity. This regularization involves rescaling the GaussBonnet (GB) coupling constant as $\alpha/(D4)$, which bypasses Lovelock's theorem and avoids Ostrogradsky instability. A noteworthy observation is that the maximally or spherically symmetric solutions for all the regularized gravities coincide in the $4D$ scenario. Considering this, we investigate the wormhole solutions in the galactic halos based on three different choices of dark matter (DM) profiles, such as Universal Rotation Curve, NavarroFrenkWhite, and Scalar Field Dark Matter with the framework of $4D$ EGB gravity. Also, the Karmarkar condition was used to find the exact solutions for the shape functions under different nonconstant redshift functions. We discussed the energy conditions for each DM profile and noticed the influence of GB coefficient $\alpha$ in violating energy conditions, especially null energy conditions. Further, some physical features of wormholes, viz. complexity factor, active gravitational mass, total gravitational energy, and embedding diagrams, have been explored.
 [9] arXiv:2406.13270 [pdf, html, other]

Title: Novel topological phenomena of timelike circular orbits for charged test particlesComments: 30 pages, 29 figuresSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
The topological approach has recently been successfully employed to investigate timelike circular orbits for massive neutral test particles. The observed vanishing topological number implies that these timelike circular orbits occur in pairs. However, the behavior of charged test particles in this regard remains unexplored. To address this issue, our study focuses on examining the influence of particle charge on the topology of timelike circular orbits within a spherically symmetrical black hole spacetime holding a nonvanishing radial electric field. We consider four distinct cases based on the charges of the particle and the black hole: unlike strong charge, unlike weak charge, like weak charge, and like strong charge. For each case, we calculate the corresponding topological number. Our results reveal that when the charge is large enough, the topological number takes a value of 1 instead of 0, which differs from the neutral particle scenario. Consequently, in cases of small charges, the timelike circular orbits appear in pairs, whereas in cases of larger charges, an additional unstable timelike circular orbit emerges. These findings shed light on the influence of the particle charge on the topological properties and number of timelike circular orbits.
 [10] arXiv:2406.13394 [pdf, html, other]

Title: Gravitational Wave Birefringence from Fuzzy Dark MatterComments: 7 pagesSubjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO); High Energy Physics  Phenomenology (hepph)
Gravitational wave (GW) birefringence is a remarkable phenomenon that can be used to test the parity violation in gravity. By coupling the fuzzy dark matter (FDM) scalar to the gravitational ChernSimons term, we explore the GW birefringence effects in the FDM background. In particular, in light of the highly oscillating granular FDM structure at the galactic scale, we are led to investigating the GW propagation in the ChernSimons gravity over the general nontrivial scalar profile, which is a natural extension of previous studies on the homogeneous and isotropic configurations. As a result, it is found that GWs of both circularly polarized modes propagate in the straight line with the speed of light, and does not show any velocity birefringence. However, when considering the imaginary part of the dispersion relation, GWs exhibit the amplitude birefringence in which one circular polarization is enhanced while the other suppressed. Due to its local nature, the FDMinduced amplitude birefringence only depends on the GW frequency without any reliance on the GW event distance. More importantly, the birefringence factor shows a periodic time variation with the period reflecting the FDM scalar mass, which is the smoking gun for testing this new birefringence mechanism. Finally, we also study the extragalactic FDM contribution to the GW birefringence, which is shown to be suppressed by the cosmological DM density and thus subdominant compared with the galactic counterpart.
 [11] arXiv:2406.13416 [pdf, html, other]

Title: Influence of thermal bath on PancharatnamBerry phase in an accelerated frameComments: Latex, 7 pages, 2 figuresSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth); Quantum Physics (quantph)
A uniformly accelerated atom captures PancharatnamBerry phase in its quantum state and the phase factor depends on the vacuum fluctuation of the background quantum fields. We observe that the thermal nature of the fields further affects the induced phase. Interestingly the induced phase captures the exchange symmetry between the Unruh and real thermal baths. This observation further supports the claim that the Unruh thermal bath mimics a real thermal bath. Moreover for certain values of system parameters and at high temperature, the phase is enhanced compared to zero temperature situation. However the required temperature to observe the phase experimentally is so high that the detection of Unruh effect through this is not possible within the current technology.
 [12] arXiv:2406.13521 [pdf, html, other]

Title: Gravitationalwave background in bouncing models from semiclassical, quantum and string gravityIdo BenDayan, Gianluca Calcagni, Maurizio Gasperini, Anupam Mazumdar, Eliseo Pavone, Udaykrishna Thattarampilly, Amresh VermaComments: 1+33 pages, 4 figuresSubjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO); High Energy Physics  Theory (hepth)
We study the primordial spectra and the gravitationalwave background (GWB) of three models of semiclassical, quantum or string gravity where the big bang is replaced by a bounce and the tensor spectrum is bluetilted: ekpyrotic universe with fastrolling Galileons, stringgas cosmology with AtickWitten conjecture and prebigbang cosmology. We find that the ekpyrotic scenario does not produce a GWB amplitude detectable by present or thirdgeneration interferometers, while the stringgas model is ruled out for producing too large a signal. In contrast, the GWB of the prebigbang scenario falls within the sensitivity window of both LISA and Einstein Telescope, where it takes the form of a single or a broken power law depending on the choice of parameters. The latter will be tightly constrained by both detectors.
 [13] arXiv:2406.13654 [pdf, html, other]

Title: Inspiralmergerringdown waveforms in EinsteinscalarGaussBonnet gravity within the effectiveonebody formalismComments: 33 pages, 11 figuresSubjects: General Relativity and Quantum Cosmology (grqc)
Gravitational waves (GWs) provide a unique opportunity to test General Relativity (GR) in the highly dynamical, strongfield regime. So far, the majority of the tests of GR with GW signals have been carried out following parametrized, theoryindependent approaches. An alternative avenue consists in developing inspiralmergerringdown (IMR) waveform models in specific beyondGR theories of gravity, by combining analytical and numericalrelativity results. In this work, we provide the first example of a full IMR waveform model in a beyondGR theory, focusing on EinsteinscalarGaussBonnet (ESGB) gravity. This theory has attracted particular attention due to its rich phenomenology for binary blackhole (BH) mergers, thanks to the presence of nontrivial scalar fields. Starting from the stateofthe art, effectiveonebody (EOB) multipolar waveform model for spinprecessing binary BHs SEOBNRv5PHM, we include theoryspecific corrections to the EOB Hamiltonian, the metric and scalar energy fluxes, the GW modes, the quasinormalmode (QNM) spectrum and the mass and spin of the remnant BH. We also propose a way to marginalize over the uncertainty in the merger morphology with additional nuisance parameters. Interestingly, we observe that changes in the frequency of the ringdown waveform due to the final mass and spin corrections are significantly larger than those due to ESGB corrections to the QNM spectrum. By performing Bayesian parameter estimation for the GW events GW190412, GW190814 and GW230529_181500, we place constraints on the fundamental coupling of the theory ($\sqrt{\alpha_{\mathrm{GB}}} \lesssim 0.31~\mathrm{km}$ at 90% confidence). The bound could be improved by one order of magnitude by observing a single "golden" binary system with nextgeneration groundbased GW detectors.
 [14] arXiv:2406.13690 [pdf, html, other]

Title: Lower bound of black hole hair in pure Lovelock theory of gravityComments: 6 pages, 1 figureSubjects: General Relativity and Quantum Cosmology (grqc)
As an alternative to the "no hair conjecture," the "no short hair conjecture" for hairy black holes was established earlier. This theorem stipulates that hair must be present above 3/2 of the event horizon radius for a hairy black hole. It is assumed that the nonlinear behavior of the matter field plays a key role in the presence of such hair. Subsequently, it was established that the hair must extend beyond the photon sphere of the corresponding black hole. We have investigated the validity of the "no short hair conjecture" in pure Lovelock gravity. Our analysis has shown that irrespective of dimensionality and Lovelock order, the hair of a static, spherically symmetric black hole extends at least up to the photon sphere.
 [15] arXiv:2406.13758 [pdf, html, other]

Title: Plane symmetric gravitational fields in (D+1)dimensional General RelativityComments: 12 pagesSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
We consider plane symmetric gravitational fields within the framework of General Relativity in (D+1)dimensional spacetime. Two classes of vacuum solutions correspond to higherdimensional generalizations of the Rindler and Taub spacetimes. The general solutions are presented for a positive and negative cosmological constant as the only source of the gravity. Matching conditions on a planar boundary between two regions with distinct plane symmetric metric tensors are discussed. An example is considered with Rindler and Taub geometries in neighboring halfspaces. As another example, we discuss a finite thickness cosmological constant slab embedded into the Minkowski, Rindler and Taub spacetimes. The corresponding surface energymomentum tensor is found required for matching the exterior and interior geometries.
 [16] arXiv:2406.13845 [pdf, html, other]

Title: Effects of quantum corrections to Lorentzian vacuum transitions in the presence of gravityComments: 36 pages, 4 figuresSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
We present a study of the vacuum transition probabilities taking into account quantum corrections. We first introduce a general method that expand previous works employing the Lorentzian formalism of the WheelerDe Witt equation by considering higher order terms in the semiclassical expansion. The method presented is applicable in principle to any model in the superspace and up to any desired order in the quantum correction terms. Then, we apply this method to obtain analytical solutions for the probabilities up to second quantum corrections for homogeneous isotropic and anisotropic universes. We use the FriedmannLemaitreRobertsonWalker with positive and zero curvature for the isotropic case and the Bianchi III and KantwowskiSachs metrics for the anisotropic case. Interpreting the results as distribution probabilities of creating universes by vacuum decay with a given size, we found that the general behaviour is that considering up to the second quantum correction leads to an avoidance of the initial singularity. However, we show that this result can only be achieved for the isotropic universe. Furthermore, we also study the effect of anisotropy on the transition probabilities.
 [17] arXiv:2406.14157 [pdf, html, other]

Title: Exact solutions for differentially rotating galaxies in general relativityComments: 5 pages, 2 figuresSubjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO); Astrophysics of Galaxies (astroph.GA); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
A class of stationary axisymmetric solutions of Einstein's equations for isolated differentially rotating dust sources is presented. The lowenergy asymptotic regime is extracted, requiring a selfconsistent coupling of quasilocal energy and angular momentum. The Raychaudhuri equation reduces to a balance equation, with two important limits. These limits can be interpreted empirically for rotationally supported configurations such as galaxies. The net energy including quasilocal kinetic contributions vanishes on the inner vortex surface, and the outer rotosurface. These new geometrical objects potentially shed light on virialization. Whether or not abundant collisionless dark matter exists, the new solutions suggest that the phenomenology of galactic rotation curves be fundamentally reconsidered, for consistency with general relativity.
 [18] arXiv:2406.14173 [pdf, html, other]

Title: TimeDelay Interferometry for ASTRODGWComments: This master's thesis was originally written in Chinese and submitted in 2011. This version is quickly translated with the assistance of ChatGPT. In Chapter 7, a secondgeneration TDI bank was developed, and some of the TDI observables are related to recent works (arXiv:2403.01490 and arXiv:2406.11305). Comments and feedback are welcomeSubjects: General Relativity and Quantum Cosmology (grqc); Instrumentation and Methods for Astrophysics (astroph.IM)
In the detection of gravitational waves in space, the arm lengths between spacecraft are not equal due to their orbital motion. Consequently, the equal arm length Michelson interferometer used in Earth laboratories is not suitable for space. To achieve the necessary sensitivity for space gravitational wave detectors, laser frequency noise must be suppressed below secondary noise sources such as optical path noise and acceleration noise. To suppress laser frequency noise, timedelay interferometry (TDI) is employed to match the two optical paths and retain gravitational wave signals. Since planets and other solar system bodies perturb the orbits of spacecraft and affect TDI performance, we simulate the time delay numerically using the CGC2.7 ephemeris framework. To examine the feasibility of TDI for the ASTRODGW mission, we devised a set of 10year and a set of 20year optimized mission orbits for the three spacecraft starting on June 21, 2028, and calculated the path mismatches in the first and secondgeneration TDI channels. The results demonstrate that all secondgeneration TDI channels meet the ASTRODGW requirements. A geometric approach is used in the analysis and synthesis of both firstgeneration and secondgeneration TDI to clearly illustrate the construction process.
 [19] arXiv:2406.14291 [pdf, html, other]

Title: PostNewtonian expansions of extreme mass ratio inspirals of spinning bodies into Schwarzschild black holesComments: 22 pages, 8 figuresSubjects: General Relativity and Quantum Cosmology (grqc); Instrumentation and Methods for Astrophysics (astroph.IM)
Spacebased gravitationalwave detectors such as LISA are expected to detect inspirals of stellarmass compact objects into massive black holes. Modeling such inspirals requires fully relativistic computations to achieve sufficient accuracy at leading order. However, subleading corrections such as the effects of the spin of the inspiraling compact object may potentially be treated in weakfield expansions such as the postNewtonian (PN) approach.
In this work, we calculate the PN expansion of eccentric orbits of spinning bodies around Schwarzschild black holes. Then we use the Teukolsky equation to compute the energy and angular momentum fluxes from these orbits up to the 5PN order. Some of these PN orders are exact in eccentricity, while others are expanded up to the tenth power in eccentricity. Then we use the fluxes to construct a hybrid inspiral model, where the leading part of the fluxes is calculated numerically in the fully relativistic regime, while the part linear in the small spin is analytically approximated using the PN series. We calculate LISArelevant inspirals and respective waveforms with this model and a fully relativistic model. Through the calculation of mismatch between the waveforms from both models we conclude that the PN approximation of the linearinspin part of the fluxes is sufficient for lower eccentricities.  [20] arXiv:2406.14345 [pdf, html, other]

Title: Revisiting the static spherically symmetric solutions of gravity with a conformally coupled scalarComments: 11 pagesSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
We revisit the static spherically symmetric solutions of Einstein's General Relativity with a conformally coupled scalar field in arbitrary dimensions. Using a four rank tensor introduced earlier we recast the field equations in a manifestly symmetric form to elucidate a somewhat lessknown feature of dual mapping between solutions. We also show that there is a twoparameter subfamily of solutions which enjoy a duality symmetry and in four dimensions both the BBMB black hole and the BarceloVisser wormhole belong to this subfamily. Along the way, we rederive the full threeparameter family of solutions by direct integration of the field equations and a natural choice of ansatz which arguably has several advantages over other previously known methods.
 [21] arXiv:2406.14552 [pdf, html, other]

Title: Exploring the nohair theorem with LISASubjects: General Relativity and Quantum Cosmology (grqc)
In this study, we explore the possibility of testing the nohair theorem with gravitational waves from massive black hole binaries in the frequency band of the Laser Interferometer Space Antenna (LISA). Based on its sensitivity, we consider LISA's ability to detect possible deviations from general relativity (GR) in the ringdown. Two approaches are considered: an agnostic quasinormal mode (QNM) analysis, and a method explicitly targeting the deviations from GR for given QNMs. Both approaches allow us to find fractional deviations from general relativity as estimated parameters or by comparing the mass and spin estimated from different QNMs. However, depending on whether we rely on the prior knowledge of the source parameters from a premerger or inspiralmergerringdown (IMR) analysis, the estimated deviations may vary. Under some assumptions, the second approach targeting fractional deviations from GR allows us to recover the injected values with high accuracy and precision. We obtain $(5\%, 10\%)$ uncertainty on ($\delta \omega, \delta \tau)$ for the $(3,3,0)$ mode, and $(3\%, 17\%)$ for the $(4,4,0)$ mode. As each approach constrains different features, we conclude that combining both methods would be necessary to perform a better test. In this analysis, we also forecast the precision of the estimated deviation parameters for sources throughout the mass and distance ranges observable by LISA.
New submissions for Friday, 21 June 2024 (showing 21 of 21 entries )
 [22] arXiv:2406.09525 (crosslist from astroph.CO) [pdf, html, other]

Title: Quantum Gravity Effects on the Tachyon Inflation from Thermodynamic PerspectiveComments: Accepted for publication in Physics of the Dark Universe,29 pages, 12 figures, 10 tablesSubjects: Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
By considering the Friedmann equations emerging from the entropyarea law of black hole thermodynamics in the context of the generalized uncertainty principle, we study tachyon inflation in the early universe. The presence of a minimal length modifies the Friedmann equations and hence the slowroll and perturbation parameters in the tachyon model. These modifications, though small, affect the viability of the tachyon inflation in confrontation with observational data. We compare the numerical results of the model with Planck2018 TT, TE, EE +lowE+lensing+BAO+BK14(18) data and Planck2018 TT, TE,EE +lowE+lensing+BK14(18) +BAO+LIGO $\&$ Virgo2016 data at $68\%$ and $95\%$ CL. We show that while the tachyon inflation with powerlaw, inverse powerlaw and inverse exponential potentials is not observationally viable in comparison with the $1\sigma$ and $2\sigma$ confidence levels of the new joint data, in the presence of the minimal length the model becomes observationally viable.
 [23] arXiv:2406.12713 (crosslist from hepth) [pdf, other]

Title: Structure of Massive Gauge/Gravity Scattering Amplitudes, Equivalence Theorems, and Extended DoubleCopy with Compactified Warped SpaceComments: 84 pagesSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph)
We study the structure of scattering amplitudes of massive KaluzaKlein (KK) states in the compactified 5dimensional warped gauge and gravity theories. We present systematic formulations of the gauge theory equivalence theorem (GAET) and the gravitational equivalence theorem (GRET) for warped KK theories in $R_\xi^{}$ gauge, where the GAET connects the scattering amplitudes of longitudinal KK gauge bosons to that of the corresponding KK Goldstone bosons and the GRET connects the scattering amplitudes of KK gravitons of helicityzero (helicityone) to that of the corresponding gravitational KK Goldstone bosons. We analyze the structure of 3point and 4point scattering amplitudes of massive KK gauge bosons and of massive KK gravitons as well as their corresponding Goldstone bosons. We first prove the GAET and GRET explicitly for the fundamental 3point KK gauge/gravity scattering amplitudes. We then demonstrate that the validity of the GAET and GRET for 4point gauge/gravity scattering amplitudes can be reduced to the validity of GAET and GRET for 3point gauge/gravity scattering amplitudes at tree level. With these, we study the doublecopy construction of KK scattering amplitudes in the warped gauge/gravity theories. We newly realize the doublecopy for massive 3point full gauge/gravity amplitudes at tree level under proper correspondences of colorkinematics and of gauge/gravity couplings, whereas we can construct the doublecopy for 4point KK gauge/gravity amplitudes to the leading order (LO) of high energy expansion. We also conjecture that this LO doublecopy construction can be extended to $N$point scattering amplitudes with $N\!\geqslant\!5$.
 [24] arXiv:2406.12855 (crosslist from math.GM) [pdf, other]

Title: Moving frame and spin field representations of submanifolds in flat spaceComments: 20 pages, 1 figureSubjects: General Mathematics (math.GM); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth); Mathematical Physics (mathph)
We introduce a spin field approach, that is compatible with the Cartan moving frame method, to describe the submanifold in a flat space. In fact, we consider a kind of spin field $\psi$, that satisfies a Killing spin field equation (analogous to a Killing spinor equation) written in terms of the Clifford algebra, and we use the spin field to locally rotate the orthonormal basis $\{\hat{e}_\mathtt{I}\}$. Then, the deformed orthonormal frame $\{\tilde{\psi}\hat{e}_\mathtt{I}\psi\}$ can be seen as the moving frame of a submanifold. We find some solutions to the Killing spin field equation and demonstrate an explicit example. Using the product of the spin fields, one can easily generate a new immersion submanifold, and this technique should be useful for studies in geometry and physics. Through the spin field, we find a linear relation between the connection and the extrinsic curvature of the submanifold. We propose a conjecture that any solution of the Killing spin field equation can be locally written as the product of the solutions we find.
 [25] arXiv:2406.12917 (crosslist from astroph.IM) [pdf, html, other]

Title: The Black Hole Explorer: Motivation and VisionMichael D. Johnson, Kazunori Akiyama, Rebecca Baturin, Bryan Bilyeu, Lindy Blackburn, Don Boroson, Alejandro CardenasAvendano, Andrew Chael, Chikwan Chan, Dominic Chang, Peter Cheimets, Cathy Chou, Sheperd S. Doeleman, Joseph Farah, Peter Galison, Ronald Gamble, Charles F. Gammie, Zachary Gelles, Jose L. Gomez, Samuel E. Gralla, Paul Grimes, Leonid I. Gurvits, Shahar Hadar, Kari Haworth, Kazuhiro Hada, Michael H. Hecht, Mareki Honma, Janice Houston, Ben Hudson, Sara Issaoun, He Jia, Svetlana Jorstad, Jens Kauffmann, Yuri Y. Kovalev, Peter Kurczynski, Robert Lafon, Alexandru Lupsasca, Robert Lehmensiek, ChungPei Ma, Daniel P. Marrone, Alan P. Marscher, Gary J. Melnick, Ramesh Narayan, Kotaro Niinuma, Scott C. Noble, Eric J. Palmer, Daniel C. M. Palumbo, Lenny Paritsky, Eliad Peretz, Dominic Pesce, Alexander Plavin, Eliot Quataert, Hannah Rana, Angelo Ricarte, Freek Roelofs, Katia Shtyrkova, Laura C. Sinclair, Jeffrey Small, Sridharan Tirupati Kumara, Ranjani Srinivasan, Andrew Strominger, Paul Tiede, Edward Tong, Jade Wang, Jonathan Weintroub, Maciek Wielgus, George Wong, Xinyue Alice ZhangComments: Proceedings for SPIE Astronomical Telescopes and InstrumentationSubjects: Instrumentation and Methods for Astrophysics (astroph.IM); Astrophysics of Galaxies (astroph.GA); High Energy Astrophysical Phenomena (astroph.HE); General Relativity and Quantum Cosmology (grqc)
We present the Black Hole Explorer (BHEX), a mission that will produce the sharpest images in the history of astronomy by extending submillimeter VeryLongBaseline Interferometry (VLBI) to space. BHEX will discover and measure the bright and narrow "photon ring" that is predicted to exist in images of black holes, produced from light that has orbited the black hole before escaping. This discovery will expose universal features of a black hole's spacetime that are distinct from the complex astrophysics of the emitting plasma, allowing the first direct measurements of a supermassive black hole's spin. In addition to studying the properties of the nearby supermassive black holes M87* and Sgr A*, BHEX will measure the properties of dozens of additional supermassive black holes, providing crucial insights into the processes that drive their creation and growth. BHEX will also connect these supermassive black holes to their relativistic jets, elucidating the power source for the brightest and most efficient engines in the universe. BHEX will address fundamental open questions in the physics and astrophysics of black holes that cannot be answered without submillimeter space VLBI. The mission is enabled by recent technological breakthroughs, including the development of ultrahighspeed downlink using laser communications, and it leverages billions of dollars of existing ground infrastructure. We present the motivation for BHEX, its science goals and associated requirements, and the pathway to launch within the next decade.
 [26] arXiv:2406.12958 (crosslist from hepth) [pdf, html, other]

Title: Unimodular Quadratic Gravity and the Cosmological ConstantComments: 6 pagesSubjects: High Energy Physics  Theory (hepth); Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc)
Unimodular gravity addresses the old cosmological constant (CC) problem, explaining why such constant is not at least as large as the largest particle mass scale, but classically it is indistinguishable from ordinary gravity. Conversely, quantum physics may give us a way to distinguish the two theories. Thus, here the unimodular constraint is imposed on a nonperturbative and backgroundindependent quantum version of quadratic gravity, which was recently formulated. It is shown that unimodularity does lead to different predictions for some inflationary quantum observables. Unimodular gravity per se does not solves the new CC problem (why the CC has the observed value?) even in this realization. To address this issue a multiverse made by different eras in a single big bang is considered and the observed scale of dark energy is explained anthropically.
 [27] arXiv:2406.13461 (crosslist from hepth) [pdf, html, other]

Title: Static neutral black holes in KalbRamond gravityComments: 22 pages, 2 figures, 1 table, JHEP3.clsSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc)
The KalbRamond (KR) gravity theory, a modified gravity theory that nonminimally couples a KR field with a nonzero vacuum expectation value for the gravitational field, can spontaneously break the Lorentz symmetry of gravity. In a recent work, Yang et al. [Phys. Rev. D 108, 124004 (2023)] successfully derived Schwarzschildlike black hole solutions both with and without a nonzero cosmological constant within the framework of KR gravity. However, their analysis did not address the more general case of static, neutral, spherically symmetric black holes. In this paper, we fill this gap by resolving the field equations to construct more general static, neutral, spherically symmetric black hole solutions both with and without a nonzero cosmological constant. Our black hole solutions are shown to obey the first law and the BekensteinSmarr mass formulas of black hole thermodynamics. Moreover, we demonstrate that our static neutral spherically symmetric AdS black hole does not always satisfy the reverse isoperimetric inequality (RII), as the isoperimetric ratio can be larger or smaller than unity depending on the placement of the solution parameters within the parameter space. This behavior contrasts with the abovementioned Schwarzschildlike AdS black hole in the KR gravity theory, which always obeys the RII. Significantly, the present more general static, neutral, spherically symmetric AdS black hole is the first example of a static AdS black hole that can violate the RII.
 [28] arXiv:2406.13481 (crosslist from quantph) [pdf, html, other]

Title: Strong Noninertial Radiative Shifts in Atomic Spectra at Low AccelerationsComments: 8+7 pages, 4 figuresSubjects: Quantum Physics (quantph); General Relativity and Quantum Cosmology (grqc)
Despite numerous proposals investigating various properties of accelerated detectors in different settings, detecting the Unruh effect remains challenging due to the typically weak signal at achievable accelerations. For an atom with frequency gap $\omega_0$, accelerated in free space, significant accelerationinduced modification of properties like transition rates and radiative energy shifts requires accelerations of the order of $\omega_0 c$. In this paper, we make the case for a suitably modified density of field states to be complemented by a judicious selection of the system property to be monitored. We study the radiative energylevel shift in inertial and uniformly accelerated atoms coupled to a massless quantum scalar field inside a cylindrical cavity. Uniformly accelerated atoms experience thermal correlations in the inertial vacuum, and the radiative shifts are expected to respond accordingly. We show that the noninertial contribution to the energy shift can be isolated and significantly enhanced relative to the inertial contribution by suitably modifying the density of field modes inside a cylindrical cavity. Moreover, we demonstrate that monitoring the radiative energy shift, as compared to transition rates, allows us to reap a stronger purelynoninertial signal. We find that a purelynoninertial radiative shift as large as 50 times the inertial energy shift can be obtained at small, experimentally achievable accelerations ($ a \sim 10^{9} \omega_{0} c$) if the cavity's radius $R$ is specified with a relative precision of $\delta R/R_{0} \sim 10^{7}$. Given that radiative shifts for inertial atoms have already been measured with high accuracy, we argue that the radiative energylevel shift is a promising observable for detecting Unruh thermality with current technology.
 [29] arXiv:2406.13671 (crosslist from hepth) [pdf, html, other]

Title: Topological Equivalence Theorem and DoubleCopy for ChernSimons Scattering AmplitudesComments: 8+5 pages, to match Journal Version. This Letter paper is a companion of the systematic longer paper arXiv:2110.05399 (46pp)Journalref: Research 6 (2023) 0072Subjects: High Energy Physics  Theory (hepth); Strongly Correlated Electrons (condmat.strel); General Relativity and Quantum Cosmology (grqc)
We study the mechanism of topological massgeneration for 3d ChernSimons gauge theories and propose a brandnew Topological Equivalence Theorem to connect scattering amplitudes of the physical gauge boson states to that of the transverse states under high energy expansion. We prove a general energy cancellation mechanism for $N$point physical gauge boson amplitudes, which predicts large cancellations of $E^{4L}\to E^{(4L) N}$ at any $L$loop level ($L\geqslant 0$). We extend the doublecopy approach to construct massive graviton amplitudes and study their structures. We newly uncover a series of strikingly large energy cancellations $E^{12}\to E^1$ of the treelevel fourgraviton scattering amplitude under high energy expansion and establish a new correspondence between the two energy cancellations in the topologically massive YangMills gauge theory and the topologically massive gravity theory. We further study the scattering amplitudes of ChernSimons gauge bosons and gravitons in the nonrelativistic limit.
 [30] arXiv:2406.13717 (crosslist from nuclth) [pdf, html, other]

Title: Beyond modified Urca: the nucleon width approximation for flavorchanging processes in dense matterComments: 6 pages, 6 figuresSubjects: Nuclear Theory (nuclth); High Energy Astrophysical Phenomena (astroph.HE); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph)
Flavorchanging charged current ("Urca") processes are of central importance in the astrophysics of neutron stars. Standard calculations approximate the Urca rate as the sum of two contributions, direct Urca and modified Urca. Attempts to make modified Urca calculations more accurate have been impeded by an unphysical divergence at the direct Urca threshold density. In this paper we describe a systematically improvable approach where, in the simplest approximation, instead of modified Urca we include an imaginary part of the nucleon mass (nucleon width). The total Urca rate is then obtained via a straightforward generalization of the direct Urca calculation, yielding results that agree with both direct and modified Urca at the densities where those approximations are valid. At low densities, we observe an enhancement of the rate by more than an order of magnitude, with important ramifications for neutron star cooling and other transport properties.
 [31] arXiv:2406.13737 (crosslist from hepth) [pdf, html, other]

Title: The Born regime of gravitational amplitudesComments: 35 pages + appendices, 6 figuresSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph)
We study the $2 \to 2$ scattering in the regime where the wavelength of the scattered objects is comparable to their distance but is much larger than any Compton wavelength in the quantum field theory. We observe that in this regime  which differs from the eikonal  the Feynman diagram expansion takes the form of a geometric series, akin to the Born series of quantum mechanics. Conversely, we can define the Feynman diagram expansion as the Born series of a relativistic effectiveonebody (EOB) Schrödinger equation. For a gravitational theory in this regime we observe that the EOB Schrödinger equation reduces to the ReggeWheeler or Teukolsky wave equations. We make use of this understanding to study the treelevel Compton scattering off a Kerr black hole. We compute the scalar and photon Compton amplitude up to $O(a^{30})$ in the black hole spin $a$ and propose an allorder expression. Remarkably, we find that boundary terms, which are typically neglected, give nonzero contact pieces necessary for restoring crossing symmetry and gauge invariance of the KerrCompton amplitude.
 [32] arXiv:2406.13747 (crosslist from astroph.CO) [pdf, html, other]

Title: Cosmological tests with bright and dark standard sirensComments: Contribution to the 2024 Cosmology session of the 58th Rencontres de MoriondSubjects: Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc)
Gravitational waves (GWs) are signals that propagate across large distances in the Universe, and thus, they bring information on the cosmic history. GW sources are at the same time distance indicators and tracers of the matter field. Events generated by binary systems can be divided into bright standard sirens, when followed by electromagnetic transients from which the redshift of the source can be measured, and the more numerous dark standard sirens, when counterparts are not available. In this proceeding, I will discuss some methods for testing the cosmological model using either bright or dark sirens and their combinations with other cosmological probes, focusing on some of my own recent contributions.
 [33] arXiv:2406.13756 (crosslist from hepph) [pdf, html, other]

Title: Multimessenger Approach to Ultralight ScalarsComments: 16 pages, 5 figures, 1 tableSubjects: High Energy Physics  Phenomenology (hepph); High Energy Astrophysical Phenomena (astroph.HE); General Relativity and Quantum Cosmology (grqc)
We propose a novel method to study the ultralight scalars, where compact rotating objects undergo the phenomenon of superradiance to create gravitational waves and neutrino flux signals. The neutrino flux results from the 'right' coupling between the ultralight scalars and the neutrinos. We study the intertwining of gravitational waves and neutrino flux signals produced from a single source and elaborate if and when the signals can be detected in existing and upcoming experiments in a direct manner. We also discuss an indirect way to test it by means of cosmic neutrino background which can be detected by upcoming PTOLEMY experiment.
 [34] arXiv:2406.13784 (crosslist from hepth) [pdf, html, other]

Title: The interplay of WGC and WCCC via charged scalar field fluxes in the RPST frameworkComments: 17 pages, 1 tableSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc)
In this paper, we investigate the weak cosmic censorship conjecture (WCCC) for the ReissnerNordstrom (RN) AdS black hole in a restricted phase space thermodynamics (RPST). Also here, we consider energy flux and equivalence massenergy principle and examine the weak gravity conjecture (WGC) and the weak cosmic censorship conjecture. The incoming and outgoing energy flux leads to changes in the black hole. In that case, by applying the first law, we examined whether the second law of thermodynamics is valid. And also one can say that, in the case where absorption and superradiance are in the saturated to an equilibrium. Also, by using the thermodynamics of black holes in the restricted phase space, we show that if the black hole is in an extreme or close to an extreme state with radiation and particle absorption, the weak cosmic censorship conjecture is established. In addition, with the help of equivalence mass and energy principle and secondorder approximation, in the near extremity, we find that when the black hole radiates and its central charge is greater than the scaled electric charge, the superradiance particles obey the weak gravity conjecture, and this causes the black hole to move further away from its extreme state. But when the particles that obey the weak gravity conjecture are attracted to the black hole when the black hole is very small. Then, in this case, we note that the black hole becomes closer to its extreme state.
 [35] arXiv:2406.13949 (crosslist from hepth) [pdf, html, other]

Title: Entanglement island and Page curve of Hawking radiation in rotating Kerr black holesSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc)
We initiate the study of the information paradox of rotating Kerr black holes by employing the recently proposed island rule. It is known that the scalar field theory near the Kerr black hole horizon can be reduced to the 2dimensional effective theory. Working within the framework of the 2dimensional effective theory and assuming the small angular momentum limit, we demonstrate that the entanglement entropy of Hawking radiation from the nonextremal Kerr black hole follows the Page curve and saturates the BekensteinHawking entropy at late times. In addition, we also discuss the effect of the black hole rotation on the Page time and scrambling time. For the extreme Kerr black hole, the entanglement entropy at late times also approximates the BekensteinHawking entropy of the extreme Kerr black hole. These results imply that entanglement islands can provide a semiclassical resolution of the information paradox for rotating Kerr black holes.
 [36] arXiv:2406.13965 (crosslist from condmat.quantgas) [pdf, html, other]

Title: Quantum analog to flapping of flags: interface instability for coflow binary superfluidsComments: 19 pages, 7 figuresSubjects: Quantum Gases (condmat.quantgas); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
We study the interface dynamics in immiscible binary superfluids using its holographic description, which naturally consists of an inviscid superfluid component and a viscous normal fluid component. We give the first theoretical realization of interface instability for two superfluid components moving with identical velocity, providing a quantum analog to the flapping of flags that is common in daily life. This behavior is in sharp contrast to the one from GrossPitaevskii equation for which no such coflow instability develops in an isolated uniform system because of Galilean invariance. The real time evolution triggered by the dynamical instability exhibits intricate nonlinear patterns leading to quantum turbulence reminiscent of the quantum KelvinHelmholtz instability. Moreover, we show that such interface dynamics is essentially different from the Landau instability for which the frictionless flow becomes thermodynamically unstable above a critical superfluid velocity. Our study uncovers the rich interface dynamics of quantum fluids and the emergence of complex flow phenomena.
 [37] arXiv:2406.14152 (crosslist from astroph.CO) [pdf, html, other]

Title: Clocking the End of Cosmic InflationComments: 24 pages, 2 figures, uses jcappubSubjects: Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
Making observable predictions for cosmic inflation requires determining when the wavenumbers of astrophysical interest today exited the Hubble radius during the inflationary epoch. These instants are commonly evaluated using the slowroll approximation and measured in efolds $\Delta N=NN_\mathrm{end}$, in reference to the efold $N_\mathrm{end}$ at which inflation ended. Slow roll being necessarily violated towards the end of inflation, both the approximated trajectory and $N_\mathrm{end}$ are determined at, typically, one or two efolds precision. Up to now, such an uncertainty has been innocuous, but this will no longer be the case with the forthcoming cosmological measurements. In this work, we introduce a new and simple analytical method, on top of the usual slowroll approximation, that reduces uncertainties on $\Delta N$ to less than a tenth of an efold.
 [38] arXiv:2406.14225 (crosslist from quantph) [pdf, html, other]

Title: Comment on "Covariant quantum field theory of tachyons"Comments: 5 pages, 1 figure; comment to arXiv:2308.00450, which was accepted by PRDSubjects: Quantum Physics (quantph); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
Recently, Paczos et al. (2308.00450) proposed a covariant quantum field theory for free and interacting tachyon fields. We show that the proposed Feynman propagator is not Lorentz invariant, proper asymptotic (in/out) tachyon states do not exist, and the proposed Smatrix describing interactions of tachyons and subluminal matter is illdefined. Since tachyons behave as bosons, interacting tachyons may also selfinteract, e.g., any interaction with ordinary matter generates such terms. As a result, the physical vacuum, instead of being at the origin of the potential, may correspond to the proper minimum of the tachyon potential, or such state does not exist at all. Our analysis indicates that quantum tachyon field does not describe a physical onshell particle with negative mass squared.
 [39] arXiv:2406.14257 (crosslist from astroph.HE) [pdf, html, other]

Title: Finding Black Holes: an Unconventional MultimessengerLaura E. Uronen, Tian Li, Justin Janquart, Hemantakumar Phurailatpam, Jason S. C. Poon, Ewoud Wempe, Léon V. E. Koopmans, Otto A. HannukselaComments: 17 pages, 4 figures. Proceedings from the Royal Society Meeting for Multimessenger Lensing (2024). Submitted to Phil. Trans. ASubjects: High Energy Astrophysical Phenomena (astroph.HE); General Relativity and Quantum Cosmology (grqc)
A rather clear problem has remained in black hole physics: localizing black holes. One of the recent theoretical ways proposed to identify black hole mergers' hosts is through multimessenger gravitational lensing: matching the properties of a lensed galactic host with those of a lensed gravitational wave. This paper reviews the most recent literature and introduces some of the ongoing work on the localization of binary black holes and their host galaxies through lensing of gravitational waves and their electromagneticallybright hosts.
 [40] arXiv:2406.14334 (crosslist from quantph) [pdf, html, other]

Title: The BoseMarlettoVedral proposal in different frames of reference and the quantum nature of gravityComments: 5 pages, 3 figuresSubjects: Quantum Physics (quantph); General Relativity and Quantum Cosmology (grqc)
Observing spatial entanglement in the BoseMarlettoVedral (BMV) experiment would demonstrate the existence of nonclassical properties of the gravitational field. We show that the special relativistic invariance of the linear regime of general relativity implies that all the components of the gravitational potential must be nonclassical. This is simply necessary in order to describe the BMV entanglement consistently across different inertial frames of reference. On the other hand, we show that the entanglement in accelerated frames could differ from that in stationary frames.
 [41] arXiv:2406.14357 (crosslist from hepth) [pdf, html, other]

Title: Black holes with electroweak hairComments: 5+8 pages, 5+1 figuresSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph)
We construct static and axially symmetric magnetically charged hairy black holes in the gravitycoupled WeinbergSalam theory. Large black holes merge with the ReissnerNordström (RN) family, while the small ones are extremal and support a hair in the form of a ringshaped electroweak condensate carrying superconducting Wcurrents and up to $22\%$ of the total magnetic charge. The extremal solutions are asymptotically RN with a mass {\it below} the total charge, $M<Q$, due to the negative Zeeman energy of the condensate interacting with the black hole magnetic field. Therefore, they cannot decay into RN black holes. As their charge increases, they show a phase transition when the horizon symmetry changes from spherical to oblate. At this point they have the mass typical for planetary size black holes of which $\approx 11\%$ are stored in the hair. Being obtained within a welltested theory, our solutions are expected to be physically relevant.
 [42] arXiv:2406.14450 (crosslist from hepth) [pdf, html, other]

Title: Hydrodynamics of Relativistic Superheated BubblesComments: 18 pages, 8 figures, 1 appendixSubjects: High Energy Physics  Theory (hepth); High Energy Astrophysical Phenomena (astroph.HE); General Relativity and Quantum Cosmology (grqc)
Relativistic, charged, superheated bubbles may play an important role in neutron star mergers if firstorder phase transitions are present in the phase diagram of Quantum Chromodynamics. We describe the properties of these bubbles in the hydrodynamic regime. We find two qualitative differences with supercooled bubbles. First, the pressure inside an expanding superheated bubble can be higher or lower than the pressure outside the bubble. Second, some fluid flows develop metastable regions behind the bubble wall. We consider the possible role of a conserved charge akin to baryon number. The fluid flow profiles are unaffected by this charge if the speed of sound is constant in each phase, but they are modified for more general equations of state. We compute the efficiency factor relevant for gravitational wave production.
 [43] arXiv:2406.14467 (crosslist from astroph.HE) [pdf, html, other]

Title: A More Precise Measurement of the Radius of PSR J0740+6620 Using Updated NICER DataAlexander J. Dittmann, M. Coleman Miller, Frederick K. Lamb, Isiah Holt, Cecilia Chirenti, Michael T. Wolff, Slavko Bogdanov, Sebastien Guillot, Wynn C. G. Ho, Sharon M. Morsink, Zaven Arzoumanian, Keith C. GendreauComments: 18 pages, 8 figures, +appendices. Accepted in ApJSubjects: High Energy Astrophysical Phenomena (astroph.HE); General Relativity and Quantum Cosmology (grqc); Nuclear Experiment (nuclex); Nuclear Theory (nuclth)
PSR J0740+6620 is the neutron star with the highest precisely determined mass, inferred from radio observations to be $2.08\pm0.07\,\rm M_\odot$. Measurements of its radius therefore hold promise to constrain the properties of the cold, catalyzed, highdensity matter in neutron star cores. Previously, Miller et al. (2021) and Riley et al. (2021) reported measurements of the radius of PSR J0740+6620 based on Neutron Star Interior Composition Explorer (NICER) observations accumulated through 17 April 2020, and an exploratory analysis utilizing NICER background estimates and a data set accumulated through 28 December 2021 was presented in Salmi et al. (2022). Here we report an updated radius measurement, derived by fitting models of Xray emission from the neutron star surface to NICER data accumulated through 21 April 2022, totaling $\sim1.1$ Ms additional exposure compared to the data set analyzed in Miller et al. (2021) and Riley et al. (2021), and to data from Xray MultiMirror (XMMNewton) observations. We find that the equatorial circumferential radius of PSR J0740+6620 is $12.92_{1.13}^{+2.09}$ km (68% credibility), a fractional uncertainty $\sim83\%$ the width of that reported in Miller et al. (2021), in line with statistical expectations given the additional data. If we were to require the radius to be less than 16 km, as was done in Salmi et al. (2024), then our 68% credible region would become $R=12.76^{+1.49}_{1.02}$ km, which is close to the headline result of Salmi et al. (2024). Our updated measurements, along with other laboratory and astrophysical constraints, imply a slightly softer equation of state than that inferred from our previous measurements.
 [44] arXiv:2406.14533 (crosslist from math.CO) [pdf, other]

Title: Local symmetries in partially ordered setsComments: 33 pages, 5 figures, 3 tablesSubjects: Combinatorics (math.CO); General Relativity and Quantum Cosmology (grqc); Mathematical Physics (mathph)
Partially ordered sets (posets) have a universal appearance as an abstract structure in many areas of mathematics. Though, even their explicit enumeration remains unknown in general, and only the counts of all partial orders on sets of up to 16 unlabelled elements have been calculated to date, see sequence A000112 in the OEIS.
In this work, we study automorphisms of posets in order to formulate a classification by local symmetries. These symmetries give rise to a division operation on the set of all posets and lead us to the construction of symmetry classes that are easier to characterise and enumerate. Additionally to the enumeration of symmetry classes, I derive polynomial expressions that count certain subsets of posets with a large number of layers (a large height). As an application in physics, I investigate local symmetries (or rather their lack of) in causal sets, which are discrete spacetime models used as a candidate framework for quantum gravity.
Cross submissions for Friday, 21 June 2024 (showing 23 of 23 entries )
 [45] arXiv:2204.09855 (replaced) [pdf, html, other]

Title: On the nonexistence of trapped surfaces under lowregularity boundsComments: 20 pages. 2 figures; minor corrections; published versionSubjects: General Relativity and Quantum Cosmology (grqc); Analysis of PDEs (math.AP); Differential Geometry (math.DG)
The emergence of trapped surfaces in solutions to the Einstein field equations is intimately tied to the wellposedness properties of the corresponding Cauchy problem in the low regularity regime. In this paper, we study the question of existence of trapped surfaces already at the level of the initial hypersurface when the scale invariant size of the Cauchy data is assumed to be bounded. Our main theorem states that no trapped surfaces can exist initially when the Cauchy data are close to the data induced on a spacelike hypersurface of Minkowski spacetime (not necessarily a flat hyperplane) in the Besov $B^{3/2}_{2,1}$ norm. We also discuss the question of extending the above result to the case when merely smallness in $H^{3/2}$ is assumed.
 [46] arXiv:2301.05679 (replaced) [pdf, html, other]

Title: Effective speed of cosmological perturbationsComments: The first version of this paper was submitted to JCAP on February 7th 2023, and the first report was received on January 14th 2024. This is a revised version based on the first referee reportJournalref: Phys.Dark Univ. 45 (2024) 101549Subjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO); High Energy Physics  Theory (hepth)
We derive an effective equation and action for comoving curvature perturbations and gravitational waves (GWs) in terms of a time, momentum and polarization dependent effective speed, encoding the effects of the interaction among metric perturbations or with other fields, such as dark energy and dark matter. The structure of the effective actions and equations is the same for scalar and tensor perturbations, and the effective actions can be written as the KleinGordon action in terms of an appropriately defined effective metric, dependent on the effective speed. The effective action reproduces, and generalizes to higher order in perturbations, results obtained for GWs in the effective field theory of inflation and dark energy, or for curvature perturbations in systems with multiple scalar fields, encoding in the effective speed the effects of both entropy and anisotropy. The effective approach can also be applied to the solutions of theories with field equations different from the Einstein equations, by defining an appropriate effective energymomentum tensor. As an example, we show that for a minimally coupled scalar field in general relativity, the effective speeds of curvature perturbations and gravitational waves are frequency and polarization dependent, due to their coupling in the action beyond the quadratic order.
 [47] arXiv:2302.12023 (replaced) [pdf, html, other]

Title: Third sound detectors in accelerated motionCameron R. D. Bunney, Vitor S. Barroso, Steffen Biermann, August Geelmuyden, Cisco Gooding, Grégoire Ithier, Xavier Rojas, Jorma Louko, Silke WeinfurtnerComments: 18 pages, 3 figures. v2: Figure 2 axis amended, typos corrected. v3: Added section 4 after referee comments, references added, author order updated, typos correctedJournalref: New J. Phys. 26 065001 (2024)Subjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
An accelerated observer moving through empty space sees particles appearing and disappearing, while an observer with a constant velocity does not register any particles. This phenomenon, generally known as the Unruh effect, relies on an initial vacuum state, thereby unifying the experience of all inertial observers. We propose an experiment to probe this observerdependent detector response, using a laser beam in circular motion as a local detector of superfluid helium4 surface modes or third sound waves. To assess experimental feasibility, we develop a theoretical framework to include a nonzero temperature initial state. We find that an accelerationdependent signal persists, independent of the initial temperature. By introducing a signaltonoise measure we show that observing this signal is within experimental reach.
 [48] arXiv:2310.15186 (replaced) [pdf, html, other]

Title: Logamediate inflation on the Swisscheese braneSubjects: General Relativity and Quantum Cosmology (grqc)
The existence of Schwarzchild black holes in the structure of Swisscheese braneworld led to the argument that this specific braneworld scenario is more realistic than the FLRW branes. In this paper, we show that a Logamediate inflation on the Swisscheese brane leads to a positive kinetic term and a negative potential with AdS minimum. While cosmic pressure is always positive, the energy density starts to get negative after a finite time and there is a time interval where both $\rho$ and $p$ are positive. Although this can be considered as a drawback of Swisscheese brane as positive energy dominates the present universe, it has been suggested that the presence of some source of negative energy could have played a significant role in early cosmic expansion. The model also suffers from the eternal inflation problem. Due to the existence of $\rho^2$ term, we have tested the new nonlinear energy conditions. The cosmographic and slowroll parameters have been investigated.
 [49] arXiv:2311.12259 (replaced) [pdf, other]

Title: Analytical models of supermassive black holes in galaxies surrounded by dark matter halosComments: revtex42, no figures. Version to appear in Phys. Lett. B 855 (2024) 138797Journalref: Phys. Lett. B 855 (2024) 138797Subjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
In this Letter, we present five analytical models in closed forms, each representing a supermassive black hole (SMBH) located at the center of a galaxy surrounded by dark matter (DM) halo. The density profile of the halo vanishes inside twice the Schwarzschild radius of the hole and satisfies the weak, strong, and dominant energy conditions. The spacetime are asymptotically flat, and the difference among the models lies in the slopes of the density profiles in the spike and regions far from the center of the galaxy. Three of them represent cusp models, whereas the other two represent core models. With the wellknown (generalized) NewmanJanis algorithm, rotating SMBHs with DM halos can be easily constructed from these models.
 [50] arXiv:2311.18238 (replaced) [pdf, html, other]

Title: The EinsteinHilbert Action for Entropically Dominant Causal SetsComments: Latex 33 pages, 13 figures. Minor corrections, fixing of typos, refining of definitions and some clarifications in the textSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
In the path integral formulation of causal set quantum gravity, the quantum partition function is a phaseweighted sum over locally finite partially ordered sets, which are viewed as discrete quantum spacetimes. It is known, however, that the number of ``layered'' sets  a class of causal sets that look nothing like spacetime manifolds  grows superexponentially with the cardinality $n$, giving an entropic contribution that can potentially dominate that of the action. We show here that in any dimension, the discrete EinsteinHilbert action for a typical $K$layered causal set reduces to the simple link action to leading order in $n$. Combined with earlier work, this completes the proof that the layered sets, although entropically dominant, are very strongly suppressed in the path sum of causal set quantum gravity whenever the discreteness scale is greater than or equal to a (mildly dimensiondependent) order one multiple of the Planck scale.
 [51] arXiv:2401.01705 (replaced) [pdf, html, other]

Title: f(R) gravity with spacetime torsionComments: EPL AcceptedSubjects: General Relativity and Quantum Cosmology (grqc)
The duality between a higher curvature $f(R)$ gravity model and a scalartensor theory helps to bring out the role of the additional degree of freedom originating from the higher derivative terms in the gravity action. Such a degree of freedom which appears as a scalar field has been shown to have multiple implications in Cosmological/Astrophysical scenario. The present work proposes a novel generalization to this correspondence between $f(R)$ gravity and a dual scalartensor theory when the affine connection is considered to have an antisymmetric part. It turns out that the $f(R)$ action in presence of spacetime torsion can be recast to a $nonminimally$ coupled scalartensor theory with a 2rank massless antisymmetric tensor field in the Einstein frame, where the scalar field gets coupled with the antisymmetric field through derivative coupling(s).
 [52] arXiv:2401.09737 (replaced) [pdf, html, other]

Title: The Equivalence Principle as a Noether SymmetryComments: 10 pages, to appear in International Journal of Geometric Methods in Modern PhysicsSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
The Equivalence Principle is considered in the framework of metricaffine gravity. We show that it naturally emerges as a Noether symmetry starting from a general nonmetric theory. In particular, we discuss the Einstein Equivalence Principle and the Strong Equivalence Principle showing their relations with the nonmetricity tensor. Possible violations are also discussed pointing out the role of nonmetricity in this debate.
 [53] arXiv:2402.02594 (replaced) [pdf, html, other]

Title: Gravitational Wave Displacement and Velocity Memory EffectsComments: 19 pagesJournalref: Class. Quantum Grav. 41 135012 2024Subjects: General Relativity and Quantum Cosmology (grqc); Analysis of PDEs (math.AP)
In this article, we compare in detail the linear and nonlinear approach to the Gravitational Waves Displacement and Velocity Memory (GWDM and GWVM) effects. We consider astrophysical situations that give rise to gravitational waves with GWVM effect, i.e. with a residual velocity (the socalled "velocitycoded memory") and discuss the possibility of future detection of the GWVM effect.
 [54] arXiv:2402.08375 (replaced) [pdf, html, other]

Title: Adiabatic approach to the transPlanckian problem in Loop Quantum CosmologyComments: 19 pages, 5 figures. v2: matches published versionSubjects: General Relativity and Quantum Cosmology (grqc)
We study the scalar modes that, being observable today, were transPlanckian before inflation, within the context of hybrid Loop Quantum Cosmology (LQC). We analyse the dynamics of these highly ultraviolet modes by introducing modified dispersion relations to their equations of motion and discuss the impact that these relations would introduce in the power spectrum by computing the adiabaticity coefficient. More precisely, we consider two different models compatible with observations for the standard linear dispersion relation which are based on different initial conditions for the perturbations and background. One of these models avoids the issue altogether by generating less $e$folds of inflation, so that the observable modes are never transPlanckian, whereas the other suffers (arguably softly) from the transPlanckian problem. This shows that the existence of the transPlanckian problem in LQC is modeldependent.
 [55] arXiv:2403.01436 (replaced) [pdf, html, other]

Title: Thermodynamics of the 3dimensional EinsteinMaxwell systemComments: 18pages, 9 figures; v3: typos corrected; v2: the introduction expanded, references and footnotes added, the implication of the result for the thermodynamics of 3dimensional gravity added to the abstract and the conclusionJournalref: JHEP 06 (2024) 134Subjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
Recently, I studied the thermodynamical properties of the EinsteinMaxwell system with a box boundary in 4dimensions [1](JHEP 04 (2024) 083). In this paper, I investigate those in 3dimensions using the zeroloop saddlepoint approximation and focusing only on a simple topology sector as usual. Similar to the 4dimensional case, the system is thermodynamically wellbehaved when $\Lambda<0$ (due to the contribution of the "bag of gold" saddles). However, when $\Lambda=0$, a crucial difference to the 4dimensional case appears, i.e. the 3dimensional system turns out to be thermodynamically unstable, while the 4dimensional one is thermodynamically stable. This may offer two options for how we think about the thermodynamics of 3dimensional gravity with $\Lambda=0$. One is that the zeroloop approximation or restricting the simple topology sector is not sufficient for 3dimensions with $\Lambda=0$. The other is that 3dimensional gravity is really thermodynamically unstable when $\Lambda=0$.
 [56] arXiv:2403.16118 (replaced) [pdf, html, other]

Title: Dynamical system analysis of LRSBI Universe with f(Q) gravity theoryComments: 18 pages, 6 figures; Published versionJournalref: Physics of the Dark Universe 46, 101556 (2024)Subjects: General Relativity and Quantum Cosmology (grqc)
Considering the Universe as a dynamic system, the understanding of its evolution is an interesting aspect of study in cosmology. Here, we investigate the anisotropic locally rotationally symmetric (LRS) Bianchi typeI (LRSBI) spacetime under the $f(Q)$ gravity of symmetric teleparallel theory equivalent to the GR (STEGR) as a dynamical system and try to understand the role of anisotropy in the evolution of its various phases. For this work, we consider two models, viz., $f(Q) = \,(Q+ 2\Lambda)$ and $f(Q) = \, \beta Q^{n}$ to study the critical points and stability of the LRSBI Universe. In both the models, it is found that the various phases like radiationdominated, matterdominated, and dark energydominated phases are heteroclinically connected, and there is some role of anisotropy in the evolution of these phases of the Universe. However, for both the models, there are some unphysical solutions too depending upon the values of model parameters $\beta$ and $n$ along with the anisotropic parameter $\alpha$.
 [57] arXiv:2403.19392 (replaced) [pdf, html, other]

Title: Tachyonic instability and spontaneous scalarization in parameterized Schwarzschildlike black holesComments: 19 pages,10 figures,published versionJournalref: Eur. Phys. J. C (2024) 84:617Subjects: General Relativity and Quantum Cosmology (grqc)
We study the phenomenon of spontaneous scalarization in parameterized Schwarzschildlike black holes. Two metrics are considered, the KonoplyaZhidenko metric and the JohannsenPsaltis metric. While these metrics can mimic the Schwarzschild black hole well in the weakfield regime, they have deformed geometries in the nearhorizon strongfield region. Such deformations notably influence the emergence of tachyonic instability and subsequent spontaneous scalarization, enabling a clear distinction between these parameterized metrics and the standard Schwarzschild metric. These results suggest a possible way to test the parameterized black holes and thus the Kerr hypothesis by observing the phenomenon of spontaneous scalarization.
 [58] arXiv:2404.01161 (replaced) [pdf, html, other]

Title: A dynamical systems formulation for inhomogeneous LRSII spacetimesComments: JCAP accepted version. Acknowledgement modifiedSubjects: General Relativity and Quantum Cosmology (grqc)
We present a dynamical system formulation for inhomogeneous LRSII spacetimes using the covariant 1+1+2 decomposition approach. Our approach describes the LRSII dynamics from the point of view of a comoving observer. Promoting the covariant radial derivatives of the covariant dynamical quantities to new dynamical variables and utilizing the commutation relation between the covariant temporal and radial derivatives, we were able to construct an autonomous system of firstorder ordinary differential equations along with some purely algebraic constraints. Using our dynamical system formulation we found several interesting features in the LRSII phase space with dust, one of them being that the homogeneous solutions constitute an invariant submanifold. For the particular case of LTB, we were also able to recover the previously known result that an expanding LTB tends to Milne in the absence of a cosmological constant, providing a potential validation of our formalism.
 [59] arXiv:2404.03364 (replaced) [pdf, html, other]

Title: High energy headon particle collisions near event horizons: classifcation of scenariosComments: 16 pages, substantial revisionSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Astrophysical Phenomena (astroph.HE); High Energy Physics  Theory (hepth)
We consider headon collisions of two particles near the event horizon. Particle 1 is outgoing, particle 2 is ingoing. We elucidate, in which case the energy $E_{c.m.}$ in the center of mass frame can grow unbounded. If the proper time between the horizon and an arbitrary point outside it for particle 1 is finite, we deal with a white hole. If it is infinite, we deal with a black hole. Particles can be either free or experience the action of a finite force. Our results are complementary to those for the standard BSW effect when particles move in the same direction. The results rely on classification of particles developed in our previous work H.V. Ovcharenko, O.B. Zaslavskii, Phys. Rev. D 108, 064029 (2023).
 [60] arXiv:2404.03779 (replaced) [pdf, html, other]

Title: Primordial black holes and induced gravitational waves in nonsingular matter bouncing cosmologyComments: Accepted at JCAPSubjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO); High Energy Physics  Theory (hepth)
We present a novel modelindependent generic mechanism for primordial black hole formation within the context of nonsingular matter bouncing cosmology. In particular, considering a short duration transition from the matter contracting phase to the Hot Big Bang expanding Universe, we find naturally enhanced curvature perturbations on very small scales which can collapse and form primordial black holes. Interestingly, the primordial black hole masses that we find can lie within the observationally unconstrained asteroidmass window, potentially explaining the totality of dark matter. Remarkably, the enhanced curvature perturbations, collapsing to primordial black holes, can induce as well a stochastic gravitationalwave background, being potentially detectable by future experiments, in particular by SKA, PTAs, LISA and ET, hence serving as a new portal to probe the potential bouncing nature of the initial conditions prevailed in the early Universe.
 [61] arXiv:2404.13025 (replaced) [pdf, html, other]

Title: Gravitational wave probes of Barrow cosmology with LISA standard sirensComments: 26 pages, 5 figuresJournalref: Journal of Cosmology and Astroparticle Physics (2024)Subjects: General Relativity and Quantum Cosmology (grqc); Cosmology and Nongalactic Astrophysics (astroph.CO)
We study the Barrow cosmological model, which proposes that quantum gravity effects create a complex, fractal structure for the universe's apparent horizon. We leverage the thermodynamics  gravity conjecture. By applying the Clausius relation to the apparent horizon of the Friedmann  Lemaître  Robertson  Walker universe within this framework, we derive modified field equations where the Barrow entropy is linked to the horizon. We assess the Barrow cosmology against current observations  cosmic microwave background , supernovae , and baryon acoustic oscillations data  and include projections for future Laser Interferometer Space Antenna (LISA) standard sirens (SS). Our numerical results suggest a modest improvement in the Hubble tension for Barrow cosmology with phantom dark energy behavior, compared to the standard cosmological model. Furthermore, incorporating simulated LISA SS data alongside existing observational constraints tightens the limitations on cosmological parameters, particularly the deformation exponent.
 [62] arXiv:2405.09945 (replaced) [pdf, html, other]

Title: Nearhorizon chaos beyond Einstein gravityComments: 21 pages, 63 figures, 1 tableSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth); Chaotic Dynamics (nlin.CD)
We investigate chaos in the dynamics of outgoing massless particles near the horizon of static spherically symmetric (SSS) black holes in two wellmotivated models of $f(R)$ gravity. In both these models, we probe chaos in the particle trajectories (under suitable harmonic confinement) in the vicinity of the black hole horizons, for a set of initial conditions. The particle trajectories, associated Poincar$\acute{e}$ sections, and Lyapunov exponents clearly illustrate the role played by the black hole horizon in the growth of chaos. We find that with increasing energy, the particle trajectories explore regions closer to the black hole horizon, with reduced overlap between two initially close trajectories. We demonstrate how this energy range is controlled by the parameters of the modified gravity theory under consideration. The growth of chaos in such a classical setting is known to respect a surface gravity bound arising from universal aspects of particle dynamics close to the black hole horizon [K. Hashimoto and N. Tanahashi, Phys. Rev. D 95, 024007 (2017)], analogous to the quantum MSS bound [J. Maldacena, S.H. Shenker and D. Stanford, JHEP 08 (2016) 106]. Interestingly, both models studied in our work respect the bound, in contrast to some of the other models of $f(R)$ gravity in the existing literature. The work serves as a motivation to use chaos as an additional tool to probe Einstein gravity in the strong gravity regime in the vicinity of black hole horizons.
 [63] arXiv:2405.15999 (replaced) [pdf, html, other]

Title: Perturbative Frequency Expansion for Nearly Monochromatic Binary Black Holes Detectable with LISAComments: 11 pages, 6 figures, corrected Eq. (15) and related errorsSubjects: General Relativity and Quantum Cosmology (grqc); High Energy Astrophysical Phenomena (astroph.HE)
The proposed space gravitational wave (GW) detector LISA has potential to detect stellarmass black hole binaries (BBHs). The majority of the detected BBHs are expected to emit nearly monochromatic GWs, whose frequency evolution will be efficiently described by Taylor expansions. We study the measurability of the associated time derivative coefficients of the frequencies, by extending a recent work based on a simplified Fisher matrix analysis. Additionally, we provide qualitative discussions on how to extract astrophysical information, such as orbital eccentricity and tertiary perturbation, from the observed derivative coefficients.
 [64] arXiv:2406.00788 (replaced) [pdf, html, other]

Title: Rotating reduced Kiselev black holes: Shadows, Energy emission and Deflection of lightComments: 23 pages, 6 figuresSubjects: General Relativity and Quantum Cosmology (grqc)
In this paper, we generate a rotating solution of the reduced Kiselev black hole through the NewmanJanis formalism. Based on such solution, we remark different shadow behaviors by varying the involved parameters $r_k, a, \alpha$. Concretely, we observe that the allowed values of the spin parameter $a$ are much less than the usual rotating black holes. By deeply analysing the shadow shapes, we show that comparable shadow shapes emerge for the same ratio $a/r_k$. On the other hand, we recognize that the parameters $a$ and $\alpha$ governs the shadow geometry while the parameter $r_k$ rules the size of such a quantity. Besides, we notice that an elliptic shadow geometry appears for certain range of relevant parameters. By making contact with the observational side, we provide a constraint on the rotating reduced Kiselev (RRK) black hole parameters. In particular, we find a good compatibility between the theoretical and experimental results. Regarding Hawking radiation, we note that the Kiselev radius $r_ k$ shows a similar behavior to the quintessence filed intensity $\mathbf{c}$. Concerning the light motion in the vicinity of a RRK black hole, we investigate deeply the deflection by varying the relevant parameters. In particular, we remark that such a quantity decreases by increasing the parameters $a$ and $\alpha$ while the opposite effect is observed when increasing $r_k$.
 [65] arXiv:2303.14156 (replaced) [pdf, html, other]

Title: NonGaussianity in rapidturn multifield inflationComments: 33 pages, 9 figuresJournalref: JCAP 03 (2024) 014Subjects: Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
We show that theories of inflation with multiple, rapidly turning fields can generate large amounts of nonGaussianity. We consider a general theory with two fields, an arbitrary fieldspace metric, and a potential that supports sustained, rapidly turning field trajectories. Our analysis accounts for nonzero field crosscorrelation and does not fix the power spectra of curvature and isocurvature perturbations to be equal at horizon crossing. Using the $\delta N$ formalism, we derive a novel, analytical formula for bispectrum generated from multifield mixing on superhorizon scales. Rapidturn inflation can produce a bispectrum with several potentially large contributions that are not necessarily of the local shape. We exemplify the applicability of our formula with a fully explicit model and show that the new contributions indeed can generate a large amplitude of local nonGaussianity, $f_{\rm NL}^{\rm loc}\sim {\cal O}(1)$. These results will be important when interpreting the outcomes of future observations.
 [66] arXiv:2306.09213 (replaced) [pdf, html, other]

Title: Stationarity and Fredholm Theory in Subextremal Kerrde Sitter SpacetimesComments: This paper is dedicated to Christian Bär's 60th birthday. The paper is a continuation and generalization of arXiv:2112.01355. Correspondingly, some assumptions and theorems are formulated the same wayJournalref: SIGMA 20 (2024), 052, 11 pagesSubjects: Analysis of PDEs (math.AP); General Relativity and Quantum Cosmology (grqc); Differential Geometry (math.DG)
In a recent paper, we proved that solutions to linear wave equations in a subextremal Kerrde Sitter spacetime have asymptotic expansions in quasinormal modes up to a decay order given by the normally hyperbolic trapping, extending the results of Vasy (2013). One central ingredient in the argument was a new definition of quasinormal modes, where a nonstandard choice of stationary Killing vector field had to be used in order for the Fredholm theory to be applicable. In this paper, we show that there is in fact a variety of allowed choices of stationary Killing vector fields. In particular, the horizon Killing vector fields work for the analysis, in which case one of the corresponding ergoregions is completely removed.
 [67] arXiv:2306.15728 (replaced) [pdf, html, other]

Title: Physicsinspired spatiotemporalgraph AI ensemble for the detection of higher order wave mode signals of spinning binary black hole mergersComments: 14 pages, 6 figures, and 3 tablesJournalref: Mach. Learn.: Sci. Technol. 5 025056 (2024) Mach. Learn.: Sci. Technol. 5 025056 Mach. Learn.: Sci. Technol. 5 025056Subjects: Instrumentation and Methods for Astrophysics (astroph.IM); Artificial Intelligence (cs.AI); General Relativity and Quantum Cosmology (grqc)
We present a new class of AI models for the detection of quasicircular, spinning, nonprecessing binary black hole mergers whose waveforms include the higher order gravitational wave modes $(l, m)=\{(2, 2), (2, 1), (3, 3), (3, 2), (4, 4)\}$, and mode mixing effects in the $l = 3, m = 2$ harmonics. These AI models combine hybrid dilated convolution neural networks to accurately model both short and longrange temporal sequential information of gravitational waves; and graph neural networks to capture spatial correlations among gravitational wave observatories to consistently describe and identify the presence of a signal in a three detector network encompassing the Advanced LIGO and Virgo detectors. We first trained these spatiotemporalgraph AI models using synthetic noise, using 1.2 million modeled waveforms to densely sample this signal manifold, within 1.7 hours using 256 A100 GPUs in the Polaris supercomputer at the ALCF. Our distributed training approach had optimal performance, and strong scaling up to 512 A100 GPUs. With these AI ensembles we processed data from a three detector network, and found that an ensemble of 4 AI models achieves stateoftheart performance for signal detection, and reports two misclassifications for every decade of searched data. We distributed AI inference over 128 GPUs in the Polaris supercomputer and 128 nodes in the Theta supercomputer, and completed the processing of a decade of gravitational wave data from a three detector network within 3.5 hours. Finally, we finetuned these AI ensembles to process the entire month of February 2020, which is part of the O3b LIGO/Virgo observation run, and found 6 gravitational waves, concurrently identified in Advanced LIGO and Advanced Virgo data, and zero false positives. This analysis was completed in one hour using one A100 GPU.
 [68] arXiv:2310.07337 (replaced) [pdf, html, other]

Title: On Penrose's Analogy between Curved Spacetime Regions and Optical LensesComments: 30 pages, 2 figures, minor correction, reference removed (published version)Journalref: Philosophy of Physics, 2(1), id.4, 2024Subjects: History and Philosophy of Physics (physics.histph); General Relativity and Quantum Cosmology (grqc)
We present a detailed analysis of Penrose's gravitooptical analogy between the focusing effects of particular families of Ricci and Weylcurved spacetime regions on the one hand, and anastigmatic and astigmatic optical lenses on the other. We put the analogy in its historical context, investigate its underlying assumptions, its range of validity, its proof of concept, and its application in Penrose's study of the notion of energy flux in general relativity. Finally, we examine the analogy within the framework of Norton's material theory of induction.
 [69] arXiv:2312.16147 (replaced) [pdf, html, other]

Title: Causal bounds on cosmological angular correlationSubjects: Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc)
We test the hypothesis that angular correlations of gravitationallyinduced temperature anisotropy in the cosmic microwave background (CMB) vanish over a range of large angular separations constrained by causality. Standard conformal geometry is used to show that if primordial quantum fluctuations generate physical correlations of gravitational potential only within compact causal diamonds bounded by inflationary horizons, the angular correlation function $C(\Theta)$ of gravitationallyinduced CMB anisotropy should exactly vanish over a significant range of angular separation around $\Theta= 90^\circ$. This geometrical causal symmetry is shown to be consistent with CMB correlations in allsky maps from the WMAP and Planck satellites, after accounting for the unmeasured dipole component and systematic measurement errors. Most significantly, the evenparity component of correlation $C_{even}(\Theta)$ is shown to be much closer to zero than previously documented, and orders of magnitude less than standard expectations. This occurrence is extremely unlikely in standard cosmological realizations based on a quantum field model: within the computed causal shadow, $\Theta= \pi/2 \pm \arcsin(1/4)$, or $75.52^\circ\lesssim\Theta\lesssim 104.48^\circ$, standard realizations are shown to produce residual correlations as small as those in the Planck maps with probabilities that range from $\simeq 10^{4.3}$ to $\simeq 10^{2.8}$. These results could signify that primordial quantum geometrical fluctuations obey a causal symmetry not included in the standard quantum field model.
 [70] arXiv:2312.17393 (replaced) [pdf, html, other]

Title: Quintessence and the Higgs Portal in the Carroll limitComments: Several references were added. To appear in PLBSubjects: High Energy Physics  Theory (hepth); High Energy Astrophysical Phenomena (astroph.HE); General Relativity and Quantum Cosmology (grqc)
A cosmological model based on two scalar fields is proposed. The first of these, $\varphi$, has mass $\mu$, while the second, $\chi$, is massless. The pair are coupled through a ``Higgs portal''. First, we show how the model reproduces the Friedmann equations if the square of the mass of the $\varphi$ field is proportional to the cosmological constant and $\chi$ represents the quintessence field. Quantum corrections break the conformal symmetry, and the $\chi$ field acquires a mass equal to $\sqrt{3g\Lambda}$. The perturbative approach with $g\ll 1$ is consistent with the bounds for $m_\chi$; moreover, by using dimensional analysis, we estimate $m_\chi \ll H_0\approx 10^{33}$ eV, which is in accordance with what is expected in the quintessence scenario. The acceleration of the universe is proportional to $\chi^2$, we conclude that for very long times, the solution of the equation of motion approaches $\langle \chi\rangle \sim {m_\chi}/{\sqrt\lambda}$ and the universe continues to accelerate, with a constant acceleration.
 [71] arXiv:2402.05720 (replaced) [pdf, html, other]

Title: Measurements of the LowAcceleration Gravitational Anomaly from the Normalized Velocity Profile of Gaia Wide Binary Stars and Statistical Testing of Newtonian and Milgromian TheoriesComments: 36 pages, 27 figures, 4 tables, ApJ, revised (Sections 2.1 & 3.4 expanded, Appendix B added)Subjects: Astrophysics of Galaxies (astroph.GA); Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Theory (hepth)
Lowacceleration gravitational anomaly is investigated with a new method of exploiting the normalized velocity profile $\tilde{v}\equiv v_p/v_c$ of wide binary stars as a function of the normalized skyprojected radius $s/r_{\rm{M}}$ where $v_p$ is the skyprojected relative velocity between the pair, $v_c$ is the Newtonian circular velocity at the skyprojected separation $s$, and $r_{\rm{M}}$ is the MOND radius. With a Monte Carlo method Gaia observed binaries and their virtual Newtonian counterparts are probabilistically distributed on the $s/r_{\rm{M}}$ versus $\tilde{v}$ plane and a logarithmic velocity ratio parameter $\Gamma$ is measured in the bins of $s/r_{\rm{M}}$. With three samples of binaries covering a broad range in size, data quality, and implied fraction of hierarchical systems including a new sample of 6389 binaries selected with accurate distances and radial velocities, I find a unanimous systematic variation from the Newtonian flat line. With $\Gamma=0$ at $s/r_{\rm{M}}\lesssim 0.15$ or $s\lesssim 1$~kilo astronomical units (kau), I get $\Gamma=0.068\pm 0.015$ (stat) $_{0.015}^{+0.024}$ (syst) for $s/r_{\rm{M}} \gtrsim 0.7$ or $s\gtrsim 5$~kau. The gravitational anomaly (i.e.\ acceleration boost) factor given by $\gamma_g = 10^{2\Gamma}$ is measured to be $\gamma_g = 1.37_{0.09}^{+0.10}$ (stat) $_{0.09}^{+0.16}$ (syst). With a reduced $\chi^2$ test of Newtonian and Milgromian nonrelativistic theories, I find that Newtonian gravity is ruled out at $5.8\sigma$ ($\chi^2_\nu=9.4$) by the new sample (and $9.2\sigma$ by the largest sample used). The Milgromian AQUAL theory is acceptable with $0.5\lesssim \chi^2_\nu\lesssim 3.1$. These results agree well with earlier results with the "accelerationplane analysis" for a variety of samples and the "stacked velocity profile analysis" for a pure binary sample.
 [72] arXiv:2403.04316 (replaced) [pdf, html, other]

Title: Testing scaleinvariant inflation against cosmological dataComments: 39 pages, 4 figures, 1 table. v2: additional references added, clarified some aspects of the analysis with regards to reheating and convergence of the results, clarified differences with respect to earlier results. Version accepted for publication in JCAPSubjects: Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc); High Energy Physics  Phenomenology (hepph); High Energy Physics  Theory (hepth)
There is solid theoretical and observational motivation behind the idea of scaleinvariance as a fundamental symmetry of Nature. We consider a recently proposed classically scaleinvariant inflationary model, quadratic in curvature and featuring a scalar field nonminimally coupled to gravity. We go beyond earlier analytical studies, which showed that the model predicts inflationary observables in qualitative agreement with data, by solving the full twofield dynamics of the system  this allows us to corroborate previous analytical findings and set robust constraints on the model's parameters using the latest Cosmic Microwave Background (CMB) data from Planck and BICEP/Keck. We demonstrate that scaleinvariance constrains the twofield trajectory such that the effective dynamics are that of a single field, resulting in vanishing entropy perturbations and protecting the model from destabilization effects. We derive tight upper limits on the nonminimal coupling strength, excluding conformal coupling at high significance. By explicitly sampling over them, we demonstrate an overall insensitivity to initial conditions. We argue that the model \textit{predicts} a minimal level of primordial tensor modes set by $r \gtrsim 0.003$, well within the reach of nextgeneration CMB experiments. These will therefore provide a litmus test of scaleinvariant inflation, and we comment on the possibility of distinguishing the model from Starobinsky and $\alpha$attractor inflation. Overall, we argue that scaleinvariant inflation is in excellent health, and possesses features which make it an interesting benchmark for tests of inflation from future CMB data.
 [73] arXiv:2403.06562 (replaced) [pdf, html, other]

Title: Hardy inequalities and uncertainty principles in the presence of a black holeSubjects: Analysis of PDEs (math.AP); General Relativity and Quantum Cosmology (grqc)
In this paper we establish Hardy and Heisenberg uncertaintytype inequalities for the exterior of a Schwarzschild black hole. The weights that appear in both inequalities are tailored to fit the geometry, and can both be compared to the related Riemannian distance from the event horizon to yield inequalities for that distance. Moreover, in both cases the classic Euclidean inequalities with a point singularity can be recovered in the limit where one stands "far enough" from the black hole, as expected from the asymptotic flatness of the metric.
 [74] arXiv:2404.18579 (replaced) [pdf, html, other]

Title: Dark energy in light of recent DESI BAO and Hubble tensionComments: 8 pages, 4 figureSubjects: Cosmology and Nongalactic Astrophysics (astroph.CO); General Relativity and Quantum Cosmology (grqc)
Recently, Dark Energy Spectroscopic Instrument (DESI) collaboration based on their first year data has reported a $\gtrsim 3\sigma$ evidence for an evolving dark energy (DE) against the cosmological constant (CC), so the standard $\Lambda$CDM model. However, it is necessary to access the impact of DESI data on the state equation $w_0$$w_a$ of DE in the Hubbletensionfree cosmologies, where $w_0$ and $w_a$ is the parameters of state equation of DE. In this paper, using recent DESI BAO measurements combined with Planck CMB and Pantheon Plus dataset, we perform the Monte Carlo Markov Chain (MCMC) analysis for the $w_0w_a$CDM model with possible prerecombination resolutions of the Hubble tension. It is found that though $w_0>1$ and $w_a<0$ are still preferred, the CC is also $<2\sigma$ consistent, while the bestfit Hubble constant $H_0$ are higher than those with preDESI BAO data but without the further exacerbation of $S_8$ tension. According to our results, the resolutions of Hubble tension are likely to suppress the \textit{preference} of DESI for the evolving DE, thus the claim of ruling out the CC needs to be more cautious regarding not only the recent observational data but also the cosmological tensions.
 [75] arXiv:2404.18733 (replaced) [pdf, html, other]

Title: Dynamical friction in the quasilinear formulation of MONDComments: 12 pages, 3 Figures. Version accepted for publication in A&ASubjects: Astrophysics of Galaxies (astroph.GA); General Relativity and Quantum Cosmology (grqc)
Aims. We explore the dynamical friction on a test mass in gravitational systems in the Quasi linear formulation of Modified Newtonian Dynamics (QuMOND). Methods. Exploiting the quasi linearity of QuMOND we derive a simple expression for the dynamical friction in akin to its Newtonian counterpart in the standard Chandrasekhar derivation. Moreover, adopting a mean field approach based on the Liouville equation we obtain a more rigorous (though in integral form) dynamical friction formula that can be evaluated numerically for a given choice of the QuMOND interpolation function. Results. Consistently with previous work, we observe that dynamical friction is stronger in MOND with respect to a baryon only Newtonian system with the same mass distribution. This amounts to a correction of the Coulomb logarithmic factor via extra terms proportional to the MOND radius of the system. Moreover, with the aid of simple numerical experiments we confirm our theoretical predictions and those of previous work on MOND.
 [76] arXiv:2405.08945 (replaced) [pdf, html, other]

Title: The secret structure of the gravitational vacuumComments: 17 pages, 5 figures, Essay awarded second prize in Gravity Research Foundation Essay Competition 2024, Comments added on the behavior of an observer inside the holeSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc)
We argue that the vacuum of quantum gravity must contain a hierarchical structure of correlations spanning all length scales. These correlated domains (called `vecros') correspond to virtual fluctuations of black hole microstates. Larger fluctuations are suppressed by their larger action, but this suppression is offset by a correspondingly larger phase space of possible configurations. We give an explicit lattice model of these vecro fluctuations, noting how their distribution changes as the gravitational pull of a star becomes stronger. At the threshold of formation of a closed trapped surface, these virtual fluctuations transition into onshell black hole microstates (fuzzballs). Fuzzballs radiate from their surface like normal bodies, resolving the information paradox. We also argue that any model without vecrotype extended vacuum correlations cannot resolve the paradox.
 [77] arXiv:2405.15594 (replaced) [pdf, html, other]

Title: Eikonal amplitudes on the celestial sphereComments: 38 pages + appendix and references, 6 figures. v2: references addedSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc)
Celestial scattering amplitudes for massless particles are Mellin transforms of momentumspace scattering amplitudes with respect to the energies of the external particles, and behave as conformal correlators on the celestial sphere. However, there are few explicit cases of welldefined celestial amplitudes, particularly for gravitational theories: the mixing between low and highenergy scales induced by the Mellin transform generically yields divergent integrals. In this paper, we argue that the most natural object to consider is the gravitational amplitude dressed by an oscillating phase arising from semiclassical effects known as eikonal exponentiation. This leads to gravitational celestial amplitudes which are analytic, apart from a set of poles at integer negative conformal dimensions, whose degree and residues we characterize. We also study the large conformal dimension limits, and provide an asymptotic series representation for these celestial eikonal amplitudes. Our investigation covers two different frameworks, related by eikonal exponentiation: $2\to2$ scattering of scalars in flat spacetime and $1\to1$ scattering of a probe scalar particle in a curved, stationary spacetime. These provide data which any putative celestial dual for Minkowski, shockwave or black hole spacetimes must reproduce. We also derive dispersion and monodromy relations for these celestial amplitudes and discuss Carrollian eikonalprobe amplitudes in curved spacetimes.
 [78] arXiv:2406.04310 (replaced) [pdf, html, other]

Title: Neural Networks Assisted MetropolisHastings for Bayesian Estimation of Critical Exponent on Elliptic Black Hole Solution in 4D Using Quantum Perturbation TheoryComments: V2: 3 extra figures for loss functions on Gaussian proposal distributions are added. Section 4 is modified. 37 pages, 14 figuresSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc); Mathematical Physics (mathph); Quantum Physics (quantph)
It is wellknown that the critical gravitational collapse produces continuous selfsimilar solutions characterized by the Choptuik critical exponent, $\gamma$. We examine the solutions in the domains of the linear perturbation equations, considering the numerical measurement errors. Specifically, we study quantum perturbation theory for the fourdimensional Einsteinaxiondilaton system of the elliptic class of $\text{SL}(2,\mathbb{R})$ transformations. We develop a novel artificial neural networkassisted MetropolisHastings algorithm based on quantum perturbation theory to find the distribution of the critical exponent in a Bayesian framework. Unlike existing methods, this new probabilistic approach identifies the available deterministic solution and explores the range of physically distinguishable critical exponents that may arise due to numerical measurement errors.
 [79] arXiv:2406.04539 (replaced) [pdf, html, other]

Title: The KLT kernel in twistor spaceComments: 53 pages + appendices and references, 13 figures. v2: references addedSubjects: High Energy Physics  Theory (hepth); General Relativity and Quantum Cosmology (grqc)
The double copy relationship between YangMills theory and general relativity can be stated in terms of a field theory KawaiLewellenTye (KLT) momentum kernel, which maps two colourordered gluon amplitudes to a graviton amplitude at treelevel. These amplitudes can also be written in compact, helicitygraded representations on twistor space which include the famous ParkeTaylor and Hodges formulae in the maximal helicity violating sector. However, a double copy formulation of these helicitygraded formulae has proved elusive. In this paper, we use graphtheoretic methods to obtain an explicit double copy representation of the treelevel, helicity graded Smatrix of general relativity in terms of a KLTlike integral kernel in twistor space. This integral kernel glues together two colourordered integrands for treelevel gluon scattering on twistor space to produce treelevel graviton amplitudes, and admits a chiral splitting into positive and negative helicity degrees of freedom. Furthermore, the kernel can be inverted to obtain a new formula for the treelevel Smatrix of biadjoint scalar theory, which we verify using recursion relations. We also derive extensions of this integral kernel to graviton scattering in antide Sitter space and selfdual radiative spacetimes, commenting on their potential double copy interpretations.