Tootfinder

This https://arxiv.org/abs/2209.11541 has been replaced.
link: https://scholar.google.com/scholar?q=a

Higgs inflation model with non-minimal coupling in hybrid Palatini approach
The inflation model with non-minimal coupling scalar field in the context of the hybrid metric Palatini is studied in this paper. We derive the Einstein's field equations, the equations of motion of the scalar field. Furthermore,the background and the perturbative parameters are obtained by means of Friedmann equation in the slow roll regime. The analysis of cosmological perturbations allowed us to obtain the main inflationary parameters such as the scalar spectral index $n_s$ and the tensor to…

Perturbations in dense matter relativistic stars induced by internal sources
Seema Satin
https://arxiv.org/abs/2404.17382 https://arx…

Perturbations in dense matter relativistic stars induced by internal sources
Einstein's field equations with a background source term that induces perturbations and the applications of this new formalism to a compact dense matter relativistic star are presented. We introduce a new response kernel in the field equations between the metric and fluid perturbations. A source term which drives or induces the sub-hydro mesoscopic scales perturbations in the astrophysical system, is of importance here. Deterministic as well as stochastic perturbations for the radial case are w…

This https://arxiv.org/abs/2307.05011 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Horizon entropy consistent with FLRW equations for general modified theories of gravity and for all EoS of the matter field
The question that continues to hinge the interrelation between cosmology and thermodynamics is broadly described as -- what is the form of horizon entropy that links the Friedmann equations for a "$general$" gravity theory with the underlying thermodynamics of the apparent horizon? The answer to this question was known only for Einstein's gravity and for $(n+1)$ dimensional Gauss-Bonnet gravity theory, but not for a general modified theory of gravity (for instance, the $F(R)$ gravity). In the p…

Infrared Sensitivity of Cosmological Probes in Horndeski Theory
Matteo Magi, Jaiyul Yoo (Zurich)
https://arXiv.org/abs/2401.15143 https://

Infrared Sensitivity of Cosmological Probes in Horndeski Theory
Cosmological probes constructed in large-scale surveys are independent of the underlying theory of gravity, and their relativistic descriptions are indeed applicable to any theory of gravity. It was shown that the presence of fluctuations with wavelength much larger than the characteristic scales of the surveys has no impact on cosmological probes, if the matter content is adiabatic and the Einstein equations are used. In this paper we study the sensitivity of cosmological probes to infrared fl…

Gauge Theoretical Method in Solving Zero-curvature Equations I. -- Application to the Static Einstein-Maxwell Equations with Magnetic Charge
Takahiro Azuma (Dokkyo University), Takao Koikawa (Institute of Human Culture Studies, Otsuma Women's University)
https://arxiv.org/abs/2403.12375<…

Gauge Theoretical Method in Solving Zero-curvature Equations I. -- Application to the Static Einstein-Maxwell Equations with Magnetic Charge
The inverse scattering problem is applied to 2-dimensional partial differential equations called soliton equations such as the KdV equation and so on. It is also used to integrate the Einstein equations with axial symmetry. These inverse scattering problems look different. We show that they can be understood in a unified way. As an application to the Einstein equation, we find solutions of the Einstein-Maxwell equations with magnetic charge.

The reverse Burnett conjecture for null dusts
Arthur Touati
https://arxiv.org/abs/2402.17530 https://arxiv.org/pdf/2402.17530<…

The reverse Burnett conjecture for null dusts
Given a generic solution $\mathbf{g}_0$ of the Einstein-null dusts system without restriction on the number of dusts, we construct families of solutions $(\mathbf{g}_λ)_{λ\in(0,1]}$ of the Einstein vacuum equations such that $\mathbf{g}_λ-\mathbf{g}_0$ and $\partial(\mathbf{g}_λ-\mathbf{g}_0)$ converges respectively strongly and weakly to 0 when $λ\to0$. Our construction, based on a multiphase geometric optics ansatz, thus extends the validity of the reverse Burnett conjecture without symm…

This https://arxiv.org/abs/2308.01078 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Black hole solutions to Einstein-Bel-Robinson gravity
In this paper, we study the physical properties of black holes in the framework of the recently proposed Einstien-Bel-Robinson gravity. We show that interestingly the theory propagates a transverse and massive graviton on a maximally symmetric background with positive energy. There is also a single ghost-free branch that returns to the Einstein case when β\to 0. We find new black hole solutions to the equations, both approximate and exact, the latter being a constant curvature black hole solut…

High angular momentum hot differentially rotating equilibrium star evolutions in conformally flat spacetime
Patrick Chi-Kit Cheong, Nishad Muhammed, Pavan Chawhan, Matthew D. Duez, Francois Foucart
https://arxiv.org/abs/2402.18529

High angular momentum hot differentially rotating equilibrium star evolutions in conformally flat spacetime
The conformal flatness approximation to the Einstein equations has been successfully used in many astrophysical applications such as initial data constructions and dynamical simulations. Although it has been shown that full general relativistic strongly differentially rotating equilibrium models deviate by at most a few percents from their conformally flat counterparts, whether those solutions share the same dynamical stabilities has not been fully addressed. To further understand the limitatio…

This https://arxiv.org/abs/2404.15792 has been replaced.
link: https://scholar.google.com/scholar?q=a

Orbits around a black bounce spacetime
In this work, the trajectories of particles around a black bounce spacetime are considered, with the Simpson-Visser model serving as an example. Trajectories for massless and massive particles are obtained through the study of null and time-like geodesics. As the Simpson-Visser solution is derived via the Einstein equations for a source involving nonlinear electrodynamics and a scalar field, photon trajectories are investigated by considering an effective metric in which photons follow null geo…

Seiberg-Witten Equations and Einstein Metrics on Finite Volume 4-Manifolds with Asymptotically Hyperbolic Ends
Alex Xu
https://arxiv.org/abs/2402.10366 htt…

Seiberg-Witten Equations and Einstein Metrics on Finite Volume 4-Manifolds with Asymptotically Hyperbolic Ends
We construct infinitely many examples of finite volume 4-manifolds with $T^3$ ends that do not admit any cusped asymptotically hyperbolic Einstein metrics yet satisfy a strict logarithmic version of the Hitchin-Thorpe inequality due to Dai-Wei. This is done by using estimates from Seiberg-Witten theory due to LeBrun as well as a method for constructing solutions to the Seiberg-Witten equations on noncompact manifolds due to Biquard. We also use constructions coming from the $Pin^-(2)$ monopole …

Gravitational Duals from Equations of State
Yago Bea, Raul Jimenez, David Mateos, Shuheng Liu, Pavlos Protopapas, Pedro Taranc\'on-\'Alvarez, Pablo Tejerina-P\'erez
https://arxiv.org/abs/2403.14763

Gravitational Duals from Equations of State
Holography relates gravitational theories in five dimensions to four-dimensional quantum field theories in flat space. Under this map, the equation of state of the field theory is encoded in the black hole solutions of the gravitational theory. Solving the five-dimensional Einstein's equations to determine the equation of state is an algorithmic, direct problem. Determining the gravitational theory that gives rise to a prescribed equation of state is a much more challenging, inverse problem. We…

Avoiding singularities in Lorentzian-Euclidean black holes: the role of atemporality
Salvatore Capozziello, Silvia De Bianchi, Emmanuele Battista
https://arxiv.org/abs/2404.17267 …

Avoiding singularities in Lorentzian-Euclidean black holes: the role of atemporality
We investigate a Schwarzschild metric exhibiting a signature change across the event horizon, which gives rise to what we term a Lorentzian-Euclidean black hole. The resulting geometry is regularized by employing the Hadamard partie finie technique, which allows us to prove that the metric represents a solution of vacuum Einstein equations. In this framework, we introduce the concept of atemporality as the dynamical mechanism responsible for the transition from a regime with a real-valued time …

Vacuum Petrov type D horizons of non-trivial $U(1)$ bundle structure over Riemann surfaces with genus $> 0$
Jerzy Lewandowski, Maciej Ossowski
https://arxiv.org/abs/2403.19383 …

Vacuum Petrov type D horizons of non-trivial $U(1)$ bundle structure over Riemann surfaces with genus $> 0$
We consider isolated horizons (Killing horizons up to the second order) whose null flow has the structure of a U(1) principal fiber bundle over a compact Riemann surface. We impose the vacuum Einstein equations (with the cosmological constant) and the condition that the spacetime Weyl tensor is of Petrov D type on the geometry of the horizons. We derive all the solutions in the case when the genus of the surface is $>1$. By doing so for all the non-trivial bundles, we complete the classificatio…

This https://arxiv.org/abs/2307.14018 has been replaced.
initial toot: https://mastoxiv.page/@…

Collective Excitations of Self-Gravitating Bose-Einstein Condensates: Breathing Mode and Appearance of Anisotropy under Self-Gravity
We investigate the collective mode of a self-gravitating Bose-Einstein condensate (BEC) described by the Gross-Pitaevskii-Poisson (GPP) equations. The self-gravitating BEC has garnered considerable attention in cosmology and astrophysics, being proposed as a plausible candidate for dark matter. Our inquiry delves into the breathing and anisotropic collective modes by numerically solving the GPP equations and using the variational method. The breathing mode demonstrates a reduction in period wit…

This https://arxiv.org/abs/2312.07486 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Dark energy from topology change induced by microscopic Gauss-Bonnet wormholes
It is known that the appearance of microscopic objects with distinct topologies and different Euler characteristics, such as instatons and wormholes, at the spacetime-foam level in Euclidean quantum gravity approaches, leads to spacetime topology changes. Such changes, in principle, may affect the field equations that arise through the semiclassical variation procedure of gravitational actions. Although in the case of Einstein-Hilbert action the presence of microscopic wormholes does not lead t…

This https://arxiv.org/abs/2309.04638 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

On the effective dynamics of Bose-Fermi mixtures
In this work, we describe the dynamics of a Bose-Einstein condensate interacting with a degenerate Fermi gas, at zero temperature. First, we analyze the mean-field approximation of the many-body Schrödinger dynamics and prove emergence of a coupled Hartree-type system of equations. We obtain rigorous error control that yields a non-trivial scaling window in which the approximation is meaningful. Second, starting from this Hartree system, we identify a novel scaling regime in which the fermion …

First investigation of void statistics in numerical relativity simulations
Michael J. Williams, Hayley J. Macpherson, David L. Wiltshire, Chris Stevens
https://arxiv.org/abs/2403.15134

First investigation of void statistics in numerical relativity simulations
We apply and extend standard tools for void statistics to cosmological simulations that solve Einstein's equations with numerical relativity (NR). We obtain a simulated void catalogue without Newtonian approximations, using a new watershed void finder which operates on fluid-based NR simulations produced with the Einstein Toolkit. We compare and contrast measures of void size and void fraction, and compare radial stacked density profiles to empirically-derived Hamaus-Sutter-Wandelt (HSW) densit…

This https://arxiv.org/abs/2401.07645 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_hept…

Nontrivial self-consistent backreaction of quantum fields in 2D dilaton gravity
We consider $(1+1)$-dimensional dilatonic black hole with two horizons, canonical temperatures of which do not coincide. We show that the presence of quantum fields in such a background leads to a substantial backreaction on the metric: 2D dilatonic analog of the semiclassical Einstein equations are solved self-consistently, and we demonstrate that taking into account of backreaction leads to a geometry with two horizons with coinciding temperatures.

This https://arxiv.org/abs/2311.15671 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

The generalized Vaidya spacetime with polytropic equation of state
The process of the gravitational collapse might lead not only to a black hole but also to naked singularity formation. In this paper, we consider the generalized Vaidya spacetime with polytropic and generalized polytropic equations of state. We solve the Einstein and Einstein-Maxwell equations to obtain the explicit form of a mass function. We consider the limiting cases of solutions and find out, that generalized Vaidya spacetime might behave like Vaidya-de Sitter and Bonnor-Vaidya-de sitter s…

Simulations of gravitational collapse in null coordinates: III. Hyperbolicity
Carsten Gundlach
https://arxiv.org/abs/2404.16720 https://

Simulations of gravitational collapse in null coordinates: III. Hyperbolicity
We investigate the well-posedness of the characteristic initial-boundary value problem for the Einstein equations in Bondi-like coordinates (including Bondi, double-null and affine). We propose a definition of strong hyperbolicity of a system of partial differential equations of any order, and show that the Einstein equations in Bondi-like coordinates in their second-order form used in numerical relativity do not meet it, in agreement with results of Giannakopoulos et al for specific first-orde…

The Spacetime Penrose Inequality for Cohomogeneity One Initial Data
Marcus Khuri, Hari Kunduri
https://arxiv.org/abs/2404.13247 https://

The Spacetime Penrose Inequality for Cohomogeneity One Initial Data
We prove the spacetime Penrose inequality for asymptotically flat $2(n+1)$-dimensional initial data sets for the Einstein equations, which are invariant under a cohomogeneity one action of $\mathrm{SU}(n+1)$. Analogous results are obtained for asymptotically hyperbolic initial data that arise as spatial hypersurfaces in asymptotically Anti de-Sitter spacetimes. More precisely, it is shown that with the dominant energy condition, the total mass is bounded below by an explicit function of the out…

This https://arxiv.org/abs/2304.13920 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_hepp…

Sound velocity peak and conformality in isospin QCD
We study zero temperature equations of state (EOS) in isospin QCD within a quark-meson model which is renormalizable and hence eliminates high density artifacts in models with the ultraviolet cutoff (e.g., NJL models). The model exhibits a crossover transition of pion condensations from the Bose-Einstein-Condensation regime at low density to the Bardeen-Cooper-Schrieffer regime at high density. The EOS stiffens quickly and approaches the quark matter regime at density significantly less than th…

This https://arxiv.org/abs/2307.10390 has been replaced.
initial toot: https://mastoxiv.page/@a…

A spin-rotation mechanism of Einstein-de Haas effect based on a ferromagnetic disk
Spin-rotation coupling (SRC) is a fundamental phenomenon that connects electronic spins with the rotational motion of a medium. We elucidate the Einstein-de Haas (EdH) effect and its inverse with SRC as the microscopic mechanism using the dynamic spin-lattice equations derived by elasticity theory and Lagrangian formalism. By applying the coupling equations to an iron disk in a magnetic field, we exhibit the transfer of angular momentum and energy between spins and lattice, with or without damp…

This https://arxiv.org/abs/2308.01728 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

A new 2D formulation of modified General Relativity
It is well known that the Einstein-Hilbert action in two dimensions is topological and yields an identically vanishing Einstein tensor. Consequently one is faced with difficulties when formulating a non-trivial gravity model. We present a new, intrinsically two-dimensional, approach to this problem based on the Einstein action. This yields a well defined variational approach which results in new field equations that break diffeomorphism invariance. Our proposed approach does not require the int…

Linear dynamics and classical tests of the gravitational quantum field theory
Yuan-Kun Gao, Da Huang, Yong-Liang Ma, Yong Tang, Yue-Liang Wu, Yu-Feng Zhou
https://arxiv.org/abs/2403.17619

Linear dynamics and classical tests of the gravitational quantum field theory
We explore the new physics phenomena of gravidynamics governed by the inhomogeneous spin gauge symmetry based on the gravitational quantum field theory. Such a gravidynamics enables us to derive the generalized Einstein equation and an equation beyond it. To simplify the analyses, we linearize the dynamic equations of gravitational interaction by keeping terms up to the leading order in the dual gravigauge field. We then apply the linearized dynamic equations into two particular gravitational p…

This https://arxiv.org/abs/2211.11791 has been replaced.
link: https://scholar.google.com/scholar?q=a

Holographic cameras: an eye for the bulk
We consider four-point correlators in an excited quantum state of a field theory. We show that, when the theory and state are holographic, a judiciously applied Fourier transform produces high-quality images of point-like bulk particles, revealing the geometry in which they move. For translation-invariant states, the bulk Einstein's equations amount to local differential equations on correlator data. In theories or states that are not holographic, images are too blurry to extract a bulk geometr…

This https://arxiv.org/abs/2210.06342 has been replaced.
link: https://scholar.google.com/scholar?q=a

Derivation of generalized Einstein's equations of gravitation in some non-inertial reference frames based on the theory of vacuum mechanics
When solving the Einstein's equations for an isolated system of masses, V. Fock introduces harmonic reference frame and obtains an unambiguous solution. Further, he concludes that there exists a harmonic reference frame which is determined uniquely apart from a Lorentz transformation if suitable supplementary conditions are imposed. It is known that wave equations keep the same form under Lorentz transformations. Thus, we speculate that Fock's special harmonic reference frames may have provided…

Static Blackhole with Cosmological Influence: Whittaker Solutions
Santanu Tripathy, K Rajesh Nayak
https://arxiv.org/abs/2404.16146 https://

Static Blackhole with Cosmological Influence: Whittaker Solutions
In this article, we investigate the impact of cosmological parameters on black holes using an exact solution to Einstein's equations that satisfies the Whittaker equation of state. We examine a spherically symmetric black hole in the background of a static Einstein Universe with a perfect fluid source with the cosmological constant. This solution is characterized by two independent parameters, namely the size of the universe~($R$) and the cosmological constant~(Lambda), representing the cosmolo…

Assessing the dark degeneracy through the gas mass fraction data
Dinorah Barbosa, Rodrigo von Marttens, Javier Gonzalez, Jailson Alcaniz
https://arxiv.org/abs/2403.12220

Assessing the dark degeneracy through the gas mass fraction data
It is well-known that Einstein's equations constrain only the total energy-momentum tensor of the cosmic substratum, without specifying the characteristics of its individual constituents. Consequently, cosmological models featuring distinct decompositions within the dark sector, while sharing identical values for the sum of dark components' energy-momentum tensor, remain indistinguishable when assessed through observables based on distance measurements. Notably, it has been already demonstrated…

Revisiting effective Einstein equations on a 3-brane in the presence of torsion
S. Khakshournia, R. Mansouri
https://arxiv.org/abs/2402.07649 https://

Revisiting effective Einstein equations on a 3-brane in the presence of torsion
The effective Einstein equations on a 3-brane embedded in a 5-dimensional Riemann-Cartan bulk spacetime are revisited. Addressing the shortcomings in the hitherto published junction conditions on the brane in the presence of torsion, we have elaborated on our general form of the junction conditions recently published. Applying our general junction conditions, we have formulated the effective Einstein equations on a Z2 symmetric brane in a standard form highlighting the difference to those publi…

The cosmological constant problem and the effective potential of a gravity-coupled scalar
Renata Ferrero, Roberto Percacci
https://arxiv.org/abs/2404.12357

The cosmological constant problem and the effective potential of a gravity-coupled scalar
We consider a quantum scalar field in a classical (Euclidean) De Sitter background, whose radius is fixed dynamically by Einstein's equations. In the case of a free scalar, it has been shown by Becker and Reuter that if one regulates the quantum effective action by putting a cutoff $N$ on the modes of the quantum field, the radius is driven dynamically to infinity when $N$ tends to infinity. We show that this result holds also in the case of a self-interacting scalar, both in the symmetric and …

Extension of Hayward black hole in $f(R)$ gravity coupled with a scalar field
G. G. L. Nashed
https://arxiv.org/abs/2404.16081 https://

Extension of Hayward black hole in $f(R)$ gravity coupled with a scalar field
This study looks into regular solutions in a theory of gravity called $f(R)$ gravity, which also involves a scalar field. The $f(R)$ theory changes Einstein's ideas by adding a new function related to something called the Ricci scalar. This lets us tweak the equations that describe how gravity works. Adding a scalar field makes the theory more interesting, giving us more ways to investigate and understand it. { The main goal of this research is to create regular black holes using a combination …

Some curvature properties of perfect fluid spacetimes
Krishnendu De, Uday Chand De, Ljubica Velimirovic
https://arxiv.org/abs/2402.15354 https://

Some curvature properties of perfect fluid spacetimes
In this paper we assume that a perfect fluid is the source of the gravitational field while analyzing the solutions to the Einstein field equations.

This https://arxiv.org/abs/2307.02925 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_nli…

Negative radiation pressure in Bose-Einstein condensates
In two-component non-linear Schrödinger equations, the force exerted by incident monochromatic plane waves on an embedded dark soliton and on dark-bright-type solitons is investigated, both perturbatively and by numerical simulations. When the incoming wave is non-vanishing only in the orthogonal component to that of the embedded dark soliton, its acceleration is in the opposite direction to that of the incoming wave. This somewhat surprising phenomenon can be attributed to the well known "neg…

This https://arxiv.org/abs/2307.06629 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

A well-balanced discontinuous Galerkin method for the first--order Z4 formulation of the Einstein--Euler system
In this paper we develop a new well-balanced discontinuous Galerkin (DG) finite element scheme with subcell finite volume (FV) limiter for the numerical solution of the Einstein--Euler equations of general relativity based on a first order hyperbolic reformulation of the Z4 formalism. The first order Z4 system, which is composed of 59 equations, is analyzed and proven to be strongly hyperbolic for a general metric. The well-balancing is achieved for arbitrary but a priori known equilibria by su…

Observation of Nonlinear Response and Onsager Regression in a Photon Bose-Einstein Condensate
Alexander Sazhin, Vladimir N. Gladilin, Andris Erglis, G\"oran Hellmann, Frank Vewinger, Martin Weitz, Michiel Wouters, Julian Schmitt
https://arxiv.org/abs/2403.04705

Observation of Nonlinear Response and Onsager Regression in a Photon Bose-Einstein Condensate
The quantum regression theorem states that the correlations of a system at two different times are governed by the same equations of motion as the temporal response of the average values. Such a relation provides a powerful framework for the investigation of physical systems by establishing a formal connection between intrinsic microscopic behaviour and a macroscopic 'effect' due to an external 'cause'. Measuring the response to a controlled perturbation in this way allows to determine, for exa…

This https://arxiv.org/abs/2306.13687 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Isometries and the double copy
In the standard derivation of the Kerr-Schild double copy, the geodicity of the Kerr-Schild vector and the stationarity of the spacetime are presented as assumptions that are necessary for the single copy to satisfy Maxwell's equations. However, it is well known that the vacuum Einstein equations imply that the Kerr-Schild vector is geodesic and shear-free, and that the spacetime possesses a distinguished vector field that is simultaneously a Killing vector of the full spacetime and the flat ba…

This https://arxiv.org/abs/2211.02603 has been replaced.
link: https://scholar.google.com/scholar?q=a

Cosmic topology. Part I. Limits on orientable Euclidean manifolds from circle searches
The Einstein field equations of general relativity constrain the local curvature at every point in spacetime, but say nothing about the global topology of the Universe. Cosmic microwave background anisotropies have proven to be the most powerful probe of non-trivial topology since, within $Λ$CDM, these anisotropies have well-characterized statistical properties, the signal is principally from a thin spherical shell centered on the observer (the last scattering surface), and space-based observa…

This https://arxiv.org/abs/2402.15675 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Einstein-Weyl geometry: A simple Weyl invariant equation for gravity
Elaborating on Einstein-Weyl geometries, we write a simple Weyl invariant equation for Gravity (with the metric and a vector field as geometrical data). The equation is linear in the curvature and a natural generalization of Einstein equations to Weyl geometry. The system has 5 physical polarizations, the graviton and a massive photon. An exact black hole solution is found. We study the dynamics on Friedman backgrounds and the evolution of cosmological perturbations. It is shown that cosmologic…

High-frequency solutions to the Einstein equations
C\'ecile Huneau, Jonathan Luk
https://arxiv.org/abs/2404.07659 https://arxiv.o…

High-frequency solutions to the Einstein equations
We review recent mathematical results concerning the high-frequency solutions to the Einstein vacuum equations and the limits of these solutions. In particular, we focus on two conjectures of Burnett, which attempt to give an exact characterization of high-frequency limits of vacuum spacetimes as solutions to the Einstein-massless Vlasov system. Some open problems and future directions are discussed.

A Post-Newtonian Analysis of Regularized 4D-EGB Theory: Complete Set of PPN Parameters and Observational Constraints
J\'unior D. Toniato, Mart\'in G. Richarte
https://arxiv.org/abs/2402.13951

A Post-Newtonian Analysis of Regularized 4D-EGB Theory: Complete Set of PPN Parameters and Observational Constraints
We performed a post-Newtonian analysis of the regularized four-dimensional Einstein-Gauss-Bonnet gravitational theory (4D-EGB). The resulting metric differs from the classical parametrized post-Newtonian (PPN) formalism in that a new gravitational potential arises from the integration of the approximate field equations. We also investigated the conserved quantities and equations of motion for massive bodies and light rays to a certain degree. By computing the predicted periastron advance rate i…

This https://arxiv.org/abs/2403.04705 has been replaced.
initial toot: https://mastoxiv.page/@…

Observation of Nonlinear Response and Onsager Regression in a Photon Bose-Einstein Condensate
The quantum regression theorem states that the correlations of a system at two different times are governed by the same equations of motion as the temporal response of the average values. Such a relation provides a powerful framework for the investigation of physical systems by establishing a formal connection between intrinsic microscopic behaviour and a macroscopic 'effect' due to an external 'cause'. Measuring the response to a controlled perturbation in this way allows to determine, for exa…

Solving the Einstein Constraints Numerically on Compact Three-Manifolds Using Hyperbolic Relaxation
Fan Zhang, Lee Lindblom
https://arxiv.org/abs/2402.08880

Solving the Einstein Constraints Numerically on Compact Three-Manifolds Using Hyperbolic Relaxation
The effectiveness of the hyperbolic relaxation method for solving the Einstein constraint equations numerically is studied here on a variety of compact orientable three-manifolds. Convergent numerical solutions are found using this method on manifolds admitting negative Ricci scalar curvature metrics, i.e. those from the $H^3$ and the $H^2\times S^1$ geometrization classes. The method fails to produce solutions, however, on all the manifolds examined here admitting non-negative Ricci scalar cur…

This https://arxiv.org/abs/2307.08867 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Spectral-infinite element method approach for computing asymptotically flat initial data sets in general relativity
In this work, we introduce a spectral-infinite element method for solving Einstein's constraint equations in hyperbolic form. As an application of this, we use this method for computing asymptotically flat perturbations of a Kerr black hole with small angular momentum. Our numerical infrastructure is based on the use of a spin-weighted spherical harmonic transform combined with an infinite element method for solving partial differential equations in unbounded domains.

This https://arxiv.org/abs/2311.13497 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Gravitational fields of axially symmetric compact objects in 5D space-time-matter gravity
In the standard Einstein's theory the exterior gravitational field of any static and axially symmetric stellar object can be described by means of a single function from which we obtain a metric into a four-dimensional space-time. In this work we present a generalization of those so called Weyl solutions to a space-time-matter metric in a five-dimensional manifold within a non-compactified Kaluza-Klein theory of gravity. The arising field equations reduce to those of vacuum Einstein's gravity w…

This https://arxiv.org/abs/2306.04832 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Stationary rotating and axially symmetric dust systems as peculiar General Relativistic objects
We study an exact solution of Einstein's equations describing a self-gravitating system, made of dust, distributed with axial symmetry and in stationary rotation, and we prove that this type of system has no Newtonian analogue. In a low-energy limit, its existence depends on the solution of a Grad-Shafranov equation in vacuum which can be interpreted as a Laplace equation for the toroidal component of the gravitomagnetic potential; in particular, in this system the relativistic rotational effec…

Generating exact polytropes in non-conservative unimodular geometries
Sudan Hansraj, Chevarra Hansraj, Njabulo Mkhize, Abdelghani Errehymy, Christian G. Boehmer
https://arxiv.org/abs/2402.07620

Generating exact polytropes in non-conservative unimodular geometries
The trace-free Einstein equations contain one equation less than the complete field equations. In a static and spherically symmetric spacetime, the number of field equations is thus reduced to two. The equation of pressure isotropy of general relativity, however, is preserved thus showing that any known perfect fluid spacetime is a suitable candidate for the trace-free scenario. The extra freedom in imposing two constraints may now be exploited to include polytopes, something that is difficult …

Imprints of Changing Mass and Spin on Black Hole Ringdown
Hengrui Zhu, Frans Pretorius, Sizheng Ma, Robert Owen, Yitian Chen, Nils Deppe, Lawrence E. Kidder, Maria Okounkova, Harald P. Pfeiffer, Mark A. Scheel, Leo C. Stein
https://arxiv.org/abs/2404.12424

Imprints of Changing Mass and Spin on Black Hole Ringdown
We numerically investigate the imprints of gravitational radiation-reaction driven changes to a black hole's mass and spin on the corresponding ringdown waveform. We do so by comparing the dynamics of a perturbed black hole evolved with the full (nonlinear) versus linearized Einstein equations. As expected, we find that the quasinormal mode amplitudes extracted from nonlinear evolution deviate from their linear counterparts at third order in initial perturbation amplitude. For perturbations lea…

This https://arxiv.org/abs/2311.11311 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Actively Learning Numerical Relativity
Data analysis of gravitational waves detected by the Ligo-Virgo-Kagra collaboration and future observatories relies on precise modelling of the sources. In order to build, calibrate and validate current models, we resort to expensive simulations in Numerical Relativity (NR), the fully-fledged simulation of Einstein's Equations. Since simulation costs and the dimensionality of parameter space are prohibitive to perform a dense coverage, approximate models interpolate among the available simulati…

This https://arxiv.org/abs/2306.02332 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

The Quasinormal Modes and Isospectrality of Bardeen (Anti-) de Sitter Black Holes
Black holes (BHs) exhibiting coordinate singularities but lacking essential singularities throughout the entire spacetime are referred to as regular black holes (RBHs). The initial formulation of RBHs was presented by Bardeen, who considered the Einstein equation coupled with a nonlinear electromagnetic field. In this study, we investigate the gravitational perturbations, including the axial and polar sectors, of the Bardeen (Anti-) de Sitter black holes. We derive the master equations with sou…

An exact stationary axisymmetric vacuum solution within a metric--affine bumblebee gravity
A. A. Ara\'ujo Filho, J. R. Nascimento, A. Yu. Petrov, P. J. Porf\'irio
https://arxiv.org/abs/2402.13014

An exact stationary axisymmetric vacuum solution within a metric--affine bumblebee gravity
Within the framework of the spontaneous Lorentz symmetry breaking, we consider a metric--affine generalization of the gravitational sector of the Standard--Model Extension (SME), including the Lorentz--violating (LV) coefficients $u$ and $s^{μν}$. In this model, we derive the modified Einstein field equations in order to obtain a new axisymmetric vacuum spinning solution for a particular bumblebee's profile. Such a solution has the remarkable property of incorporating the effects of Lorentz s…

Sachs equations and plane waves, I: Rosen universes
Jonathan Holland, George Sparling
https://arxiv.org/abs/2402.07036 https://arxiv.…

Sachs equations and plane waves, I: Rosen universes
This article, the first in a series, analyzes the general theory of plane wave spacetimes. Following Dmitri Aleekseevsky, these are defined as spacetimes admitting a group of dilations leaving invariant a smooth curve. If this curve is specified as part of the structure, the spacetime is termed a Penrose limit, whose theory was developed first by Roger Penrose. The main result is that every plane wave is a Rosen universe, a generalization of the smooth metrics of Albert Einstein and Nathan Rose…

Influence of the cosmological constant on $\kappa$-deformed Neutron Star
Bhagya. R, Diganta Parai, Harsha Sreekumar, Suman Kumar Panja
https://arxiv.org/abs/2404.08381

Influence of the cosmological constant on $κ$-deformed Neutron Star
We study a model of the neutron star in $κ$-deformed space-time in the presence of the cosmological constant ($Λ$). The Einstein tensor and the energy-momentum tensor are generalized to $κ$-deformed space-time and we construct the field equations with the cosmological constant. Considering the interior of the star to be a perfect fluid as in the commutative case, we find the Tolman-Oppenheimer-Volkoff equations with the inclusion of the cosmological constant in $κ$-deformed space-time. The …

Inflationary dynamics in modified gravity models
R. R. Cuzinatto, L. G. Medeiros
https://arxiv.org/abs/2404.11904 https://arxiv.org/p…

Inflationary dynamics in modified gravity models
Higher-order theories of gravity are a branch of modified gravity wherein the geometrodynamics of the four-dimensional Riemannian manifold is determined by field equations involving derivatives of the metric tensor of order higher than two. This paper considers a general action built with the Einstein-Hilbert term plus additional curvature-based invariants, viz. the Starobinsky $R^{2}$-type term, a term scaling with $R^{3}$, and a correction of the type $R\square R$. The focus is on the backgro…

This https://arxiv.org/abs/2310.10144 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Cosmology based on entropy
At present, there is practically no doubt that general relativity is closely related to gravity. Moreover, after the work of Jacobson, Padmanabhan and others, it became clear that a thermodynamic interpretation of Einstein's relativistic equations is possible. On the other hand, we are witnessing the conceptual problems of the SCM (the problem of the cosmological constant, the problem of coincidences) and many years of futile attempts to directly fix the main components of the model (dark energ…

This https://arxiv.org/abs/2402.15675 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Einstein-Weyl geometry: A simple Weyl invariant equation for gravity
Elaborating on Einstein-Weyl geometries, we write a simple Weyl invariant equation for Gravity (with the metric and a vector field as geometrical data). The equation is linear in the curvature and a natural generalization of Einstein equations to Weyl geometry. The system has 5 physical polarizations, the graviton and a massive photon. An exact black hole solution is found. We study the dynamics on Friedman backgrounds and the evolution of cosmological perturbations. It is shown that cosmologic…

On the weak and strong field effects in antiscalar background
Eduard Mychelkin, Maxim Makukov, Gulnara Suliyeva, Nosratollah Jafari
https://arxiv.org/abs/2403.11610

On the weak and strong field effects in antiscalar background
The triumph of general relativity under the banner "gravity is geometry" began with confirming the crucial effects within the Solar system and proceeded recently to the strong-field shadow effect for the compact object in the center of the Milky Way. Here, we examine some of those phenomena for the Einstein-scalar equations in the antiscalar regime to reveal the difference from vacuum both in weak and strong fields. As a result, we find that for week-field perihelion shift the difference betwee…

Accelerating Airy tensor modes of cosmological gravitational waves
Claudio Aravena-Plaza, V\'ictor Mu\~noz, Felipe A. Asenjo
https://arxiv.org/abs/2403.05421

Accelerating Airy tensor modes of cosmological gravitational waves
From a classical analysis, it is shown that the nondiffractive accelerating gravitational Airy wave packets are solutions of Einstein equations for their linearized tensor modes in a Friedmann-Lemaître-Robertson-Walker cosmological background filled with a perfect fluid, with equations of state $w=1/3$ and $w=-1/3$. These solutions have finite energy, presenting accelerating behavior due to the structured spatial form of the wavepacket. This is manifested by curved trajectories along the wave …

A New Perspective on Kaluza-Klein Theories
L Horoto, F G Scholtz
https://arxiv.org/abs/2404.05302 https://arxiv.org/pdf/2404.05302

A New Perspective on Kaluza-Klein Theories
By assuming that the geometry of spacetime is uniquely determined by the energy momentum tensor of matter alone, i.e. without any interactions, enables us to construct the Lagrangian from which the metric of higher dimensional spacetime follows. From the geodesic equations that follow it becomes clear that the incorrect mass of elementary particles predicted by Kaluza-Klein theories arises from the assumption that in the absence of gravity the solution to the Einstein field equations reduces to…

This https://arxiv.org/abs/2402.13951 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

A Post-Newtonian Analysis of Regularized 4D-EGB Theory: Complete Set of PPN Parameters and Observational Constraints
We performed a post-Newtonian analysis of the regularized four-dimensional Einstein-Gauss-Bonnet gravitational theory (4D-EGB). The resulting metric differs from the classical parametrized post-Newtonian (PPN) formalism in that a new gravitational potential arises from the integration of the approximate field equations. We also investigated the conserved quantities and equations of motion for massive bodies and light rays to a certain degree. By computing the predicted periastron advance rate i…

Spacetimes with homogeneous and isotropic expansion
Leandro G. Gomes
https://arxiv.org/abs/2404.07757 https://arxiv.org/pdf/2404.0775…

Spacetimes with homogeneous and isotropic expansion
In this short note, we define and characterize all the spacetimes admitting observers to whom the cosmic expansion is homogeneous and isotropic and interpret their Einstein's equations.

The Nature of Dark Energy and Constraints on Its Hypothetical Constituents from Force Measurements
Galina L. Klimchitskaya, Vladimir M. Mostepanenko
https://arxiv.org/abs/2403.05988

The Nature of Dark Energy and Constraints on Its Hypothetical Constituents from Force Measurements
This review considers the theoretical approaches to the understanding of dark energy which comprises approximately 68\% of the energy of our Universe and explains an acceleration in its expansion. Following a discussion of the main approach based on Einstein's equations with the cosmological term, the explanations of dark energy using the concept of some kind of scalar field are elucidated. These include the concept of a quintessence and modifications of the general theory of relativity by mean…

This https://arxiv.org/abs/2311.01863 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Gravitational Waves Generated by Null Cosmic Strings
Null cosmic strings are shown to disturb gravitational fields of massive bodies and create outgoing gravitational waves (GW). Perturbations of the metric caused by a straight null string and a point-like massive source are found as solutions to linearized Einstein equations on a flat space-time. An analytic approximation for their asymptotic at future null infinity is derived. A space-time created by the source and the string is shown to have asymptotically polyhomogeneous form. We calculate GW…

Graviton mass due to dark energy as a superconducting medium: theoretical and phenomenological aspects
Nader Inan, Ahmed Farag Ali, Kimet Jusufi, Abdelrahman Yasser
https://arxiv.org/abs/2404.03872

Graviton mass due to dark energy as a superconducting medium: theoretical and phenomenological aspects
It is well known that the cosmological constant term in the Einstein field equations can be interpreted as a stress tensor for dark energy. This stress tensor is formally analogous to an elastic constitutive equation in continuum mechanics. As a result, the cosmological constant leads to a "shear modulus" and "bulk modulus" affecting all gravitational fields in the universe. The form of the constitutive equation is also analogous to the London constitutive equation for a superconductor. Treatin…

This https://arxiv.org/abs/2101.04955 has been replaced.
link: https://scholar.google.com/scholar?q=a

On the geometry of silent and anisotropic big bang singularities
This article is the second of two in which we develop a geometric framework for analysing silent and anisotropic big bang singularities. In the present article, we record geometric conclusions obtained by combining the geometric framework with Einstein's equations. The main features of the results are the following: The assumptions do not involve any symmetry requirements and are weak enough to be consistent with most big bang singularities for which the asymptotic geometry is understood. The f…

This https://arxiv.org/abs/2101.04955 has been replaced.
link: https://scholar.google.com/scholar?q=a

On the geometry of silent and anisotropic big bang singularities
This article is the second of two in which we develop a geometric framework for analysing silent and anisotropic big bang singularities. In the present article, we record geometric conclusions obtained by combining the geometric framework with Einstein's equations. The main features of the results are the following: The assumptions do not involve any symmetry requirements and are weak enough to be consistent with most big bang singularities for which the asymptotic geometry is understood. The f…

This https://arxiv.org/abs/2306.06645 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Probe the equation of state for neutron stars with captured primordial black holes inside
Gravitational waves (GWs) from primordial black holes (PBHs) inspiralling inside neutron stars (NSs) within the Galaxy are detectable by ground-based detectors and provide a unique insight into the interior structure of NSs. To provide the most accurate templates for GW searches, we solve the Einstein equations inside NSs, and calculate the orbital motion of the captured PBH by taking the dynamical friction, accretion, and gravitational radiation into account. Armed with the most accurate GW wa…

This https://arxiv.org/abs/2306.06645 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Probe the equation of state for neutron stars with captured primordial black holes inside
Gravitational waves (GWs) from primordial black holes (PBHs) inspiralling inside neutron stars (NSs) within the Galaxy are detectable by ground-based detectors and provide a unique insight into the interior structure of NSs. To provide the most accurate templates for GW searches, we solve the Einstein equations inside NSs, and calculate the orbital motion of the captured PBH by taking the dynamical friction, accretion, and gravitational radiation into account. Armed with the most accurate GW wa…

Super-extremal black holes in the quasitopological electromagnetic field theory
Shahar Hod
https://arxiv.org/abs/2404.03744 https://a…

Super-extremal black holes in the quasitopological electromagnetic field theory
It has recently been proved that a simple generalization of electromagnetism, referred to as quasitopological electromagnetic field theory, is characterized by the presence of dyonic black-hole solutions of the Einstein field equations that, in certain parameter regions, are characterized by four horizons. In the present compact paper we reveal the existence, in this non-linear electrodynamic field theory, of super-extremal black-hole spacetimes that are characterized by the four degenerate fun…

This https://arxiv.org/abs/1712.10045 has been replaced.
link: https://scholar.google.com/scholar?q=a

Nonlinear stability of self-gravitating massive fields
We consider the global evolution problem for Einstein's field equations in the near-Minkowski regime and study the long-time dynamics of a massive scalar field evolving under its own gravitational field. We establish the existence of a globally hyperbolic Cauchy development associated with any initial data set that is sufficiently close to a data set in Minkowski spacetime. In addition to applying to massive fields, our theory allows us to cover metrics with slow decay in space. The strategy of…

Bose and Fermi gases in metric-affine gravity and linear Generalized Uncertainty Principle
Aneta Wojnar, D\'ebora Aguiar Gomes
https://arxiv.org/abs/2404.03345

Bose and Fermi gases in metric-affine gravity and linear Generalized Uncertainty Principle
We examine the relationship between Palatini-like theories of gravity and models incorporating linear generalized uncertainty principles. Additionally, we delve into the thermodynamics of systems comprising both Bose and Fermi gases. Our analysis encompasses the equations of state for various systems, including general Fermi gases, degenerate Fermi gases, Boltzmann gases, Bose gases such as phonons and photons, as well as Bose-Einstein condensates and liquid helium.

Bose and Fermi gases in metric-affine gravity and linear Generalized Uncertainty Principle
Aneta Wojnar, D\'ebora Aguiar Gomes
https://arxiv.org/abs/2404.03345

Bose and Fermi gases in metric-affine gravity and linear Generalized Uncertainty Principle
We examine the relationship between Palatini-like theories of gravity and models incorporating linear generalized uncertainty principles. Additionally, we delve into the thermodynamics of systems comprising both Bose and Fermi gases. Our analysis encompasses the equations of state for various systems, including general Fermi gases, degenerate Fermi gases, Boltzmann gases, Bose gases such as phonons and photons, as well as Bose-Einstein condensates and liquid helium.

This https://arxiv.org/abs/2404.00867 has been replaced.
link: https://scholar.google.com/scholar?q=a

Smoothing and flattening the universe through slow contraction versus inflation
In a systematic study, we use an equivalent pair of improved numerical relativity codes based on a tetrad-formulation of the classical Einstein-scalar field equations to examine whether slow contraction or inflation (or both) can resolve the homogeneity, isotropy and flatness problems. Our finding, based on a set of gauge/frame invariant diagnostics, is that slow contraction robustly and rapidly smooths and flattens spacetime beginning from initial conditions that are outside the perturbative r…

This https://arxiv.org/abs/2401.15809 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_grqc_…

Particle dynamics in spherically symmetric electro-vacuum instantons
In this paper, we study the geodesic motion in spherically symmetric electro-vacuum Euclidean solutions of the Einstein equation. There are two kinds of such solutions: the Euclidean Reissner-Nordström (ERN) metrics, and the Bertotti-Robinson-like (BR) metrics, the latter having constant Kretschmann scalar. First, we derive the motion equations for the ERN spacetime and we generalize the results of Battista-Esposito, showing that all orbits in as ERN spacetime are unbounded if and only if it h…

This https://arxiv.org/abs/2401.08346 has been replaced.
link: https://scholar.google.com/scholar?q=a

Graviton-Photon Oscillations in an Expanding Universe
Through the Gertsenshtein effect, the presence of a large external B-field may allow photons and gravitons to mix in a way that resembles neutrino oscillations and is even more similar to axion-photon mixing. Assuming a background B-field (or any field that behaves like one), we examine the Gertsenshtein mechanism in the context of FLRW expanding universe models, as well as de Sitter space. The conformal invariance of Maxwell's equations and the conformal noninvariance of the Einstein equations…