General Relativity and Gravitation最新文献

In this study, authors investigate a novel framework incorporating exponential electrodynamics and d-dimensional energy-dependent massive gravity. Our focus lies in demonstrating that a nonlinear electromagnetic field, acting as the gravitational source, leads to an accelerated expansion of the universe. Employing massive gravity’s rainbow as a catalyst for cosmic evolution, the big bang singularity inherent in the model is successfully eliminated. This analysis reveals that the synergy between the magnetic universe and massive gravity’s rainbow is the underlying cause of the observed accelerated cosmic expansion. The classical stability during the deceleration phase and ensure the causality of the model are established. Additionally, we delve into 4-dimensional energy-dependent cosmology. Furthermore, approximations for key cosmological parameters such as the running of the spectral index, tensor-to-scalar ratio, and, the spectral index are presented. These estimations closely align with observational data from PLANCK and WMAP, providing valuable insights into the compatibility of the proposed model with empirical evidence.

In this article, we attempt to explore the dark sector of the universe i.e. dark matter and dark energy, where the dark energy components are related to the modified f(Q) Lagrangian, particularly a power law function (f(Q)= gamma left( frac{Q}{Q_0}right) ^n), while the dark matter component is described by the Extended Bose–Einstein Condensate (EBEC) equation of state for dark matter, specifically, (p = alpha rho + beta rho ^2). We find the corresponding Friedmann-like equations and the continuity equation for both dark components along with an interacting term, specifically (mathcal {Q} = 3b^2H rho ), which signifies the energy exchange between the dark sector of the universe. Further, we derive the analytical expression of the Hubble function, and then we find the best-fit values of free parameters utilizing the Bayesian analysis to estimate the posterior probability and the Markov Chain Monte Carlo (MCMC) sampling technique corresponding to CC+Pantheon+SH0ES samples. In addition, to examine the robustness of our MCMC analysis, we perform a statistical assessment using the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). Further from the evolutionary profile of the deceleration parameter and the energy density, we obtain a transition from the decelerated epoch to the accelerated expansion phase, with the present deceleration parameter value as (q(z=0)=q_0=-0.56^{+0.04}_{-0.03}) ((68 %) confidence limit), that is quite consistent with cosmological observations. In addition, we find the expected positive behavior of the effective energy density. Finally, by examining the sound speed parameter, we find that the assumed theoretical f(Q) model is thermodynamically stable.

Hawking’s black hole area theorem was proven using the null energy condition (NEC), a pointwise condition violated by quantum fields. The violation of the NEC is usually cited as the reason that black hole evaporation is allowed in the context of semiclassical gravity. Here we provide two generalizations of the classical black hole area theorem: first, a proof of the original theorem with an averaged condition, the weakest possible energy condition to prove the theorem using focusing of null geodesics. Second, a proof of an area-type result that allows for the shrinking of the black hole horizon but provides a bound on it. This bound can be translated to a bound on the black hole evaporation rate using a condition inspired from quantum energy inequalities. Finally, we show how our bound can be applied to two cases that violate classical energy conditions.

We investigate the turnaround radius of the Reissner–Nordström deSitter Spacetime and how the turnaround radius changes if a test particle carries charge. We also consider the Martínez–Troncoso–Zanelli (MTZ) solution of conformally coupled gravity and investigate how the turnaround radius changes for a scalar test charge. In both scalar and electric interaction cases we find that the Turnaround Radius depends on the particle’s energy.

We study photon rings of constant scalar hairy black holes with mass m, charge Q, and scalar hair S obtained from the Einstein-Maxwell-conformally coupled scalar theory. These black holes are classified as scalar hairy Reissner-Nordström (SHRN) black hole, scalar hairy charged black hole with (S> -Q^2), and mutated-RN black hole. The first two respect both dominant and strong energy conditions and have positive ADM mass and entropy, while the last does not respect two energy conditions and has negative ADM mass and entropy. We find that all of these black holes respect the lower bound ((r_gamma ge 1.2 r_+)) of photon rings. We obtain all real bounds of photon rings for these black holes and discuss physical and observational properties of real bounds. It is shown that the observationally favored region based on the shadow radius includes SHRN black hole, scalar hairy charged black hole, and mutated-RN black hole.

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 solutions. Moreover, we explicitly show, that the part of solution, which depends on the polytropic index, is similar to cosmological fields surrounding both Vaidya and Bonnor–Vaidya black holes. The process of the gravitational collapse has been then considered. We have found out that the conditions of the naked singularity formation don’t depend on the polytropic index.

We study here a novel application of Kim and Lee charged wormholes assuming them to be dark halo objects playing the role of lenses in the Galactic microlensing with source stars belonging to the Galactic Bulge and the Large Magellanic Cloud. First, we observe that both the backreacted scalar ((alpha )) and electrically (Q) charged wormholes have the same zero ADM mass as has the background Ellis–Bronnikov wormhole having a special equation of state parameter (gamma = - 1). In particular, we argue that, for (alpha ne 0), the solution formally resembles, but can at best be sourcewise different from, that of the background wormhole. The charge ((Qne 0)) thus provides an extra degree of freedom that introduces a non-trivial redshift function (Phi ) to the background, alters its throat radius to (r_{{text {th}}}), yet keeps the wormhole massless. Second, we focus on this electrically charged case and calculate the light deflection angle up to 4th PPN order, analyze the effect of Q on the lensing observables such as the image positions, magnification, centroid and time delay of images of the source stars. Third, we analyze the probabilistic features such as optical depth and event rate estimated on the basis of the hypothesis that the wormhole lens could be bound or unbound to our Galaxy. Finally, we report an intriguing qualitative prediction that, compared to the Schwarzschild black hole, the Paczyński light curves of the electrically charged wormhole are much dimmer that also show characteristic gutters at the times the source enters and exits the Einstein ring. The gutters gradually come together as Q approaches the extreme limit (frac{r_{{text {th}}}}{sqrt{2}}), at which the Einstein radius (R_{E}) vanishes so that the source crosses it instantly. It is speculated that re-analyzing past data on Galactic microlensing may betray the presence of charged wormholes.

It has been recently shown in Chatterjee and Ghosh (Phys Rev Lett 125:041302, 2020, https://doi.org/10.1103/PhysRevLett.125.041302) that microstate counting carried out for quantum states residing on the horizon of a black hole leads to a correction of the form (exp (-A/4l_p^2)) in the Bekenstein-Hawking form of the black hole entropy. In this paper, we develop a novel approach to obtain the possible form of the spacetime geometry from the entropy of the black hole for a given horizon radius. The uniqueness of this solution for a given energy-momentum tensor has also been discussed. Remarkably, the black hole geometry reconstructed has striking similarities to that of noncommutative-inspired Schwarzschild black holes (Nicolini et al. in Phys Lett B 632:547, 2006). We also obtain the matter density functions using Einstein field equations for the geometries we reconstruct from the thermodynamics of black holes. These also have similarities to that of the matter density function of a noncommutative-inspired Schwarzschild black hole. The conformal structure of the metric is briefly discussed and the Penrose–Carter diagram is drawn. We then compute the Komar energy and the Smarr formula for the effective black hole geometry and compare it with that of the noncommutative-inspired Schwarzschild black hole. We also discuss some astrophysical implications of the solutions. Finally, we propose a set of quantum Einstein vacuum field equations, as a solution of which we obtain one of the spacetime solutions obtained in this work. We then show a direct connection between the quantum Einstein vacuum field equations and the first law of black hole thermodynamics.

We study the evolution of various measures of quantumness of the curvature perturbation by integrating out the inaccessible entropic fluctuations in the multi-field models of inflation. In particular, we discuss the following measures of quantumness, namely purity, entanglement entropy and quantum discord. The models being considered in this work are ones that produce large scale curvature power spectra similar to those produced by single-field models of inflation. More specifically, we consider different multi-field models which generate nearly scale invariant and oscillatory curvature power spectrum and compare their quantum signatures in the perturbations with the corresponding single-field models. We find that, even though different models of inflation may produce the same observable power spectrum on large scales, they have distinct quantum signatures arising from the perturbation modes. This may allow for a way to distinguish between different models of inflation based on their quantum signatures. Intriguingly, this result generalizes to bouncing scenarios as well.

Black holes exert quantum pressure coming from the nonlocal gravity correction. We investigate this nonlocal correction for black holes in anti-de Sitter (AdS) spacetime and its dual boundary field theory. We show that the second order curvature and the nonlocal actions do not backreact on the AdS black hole metric. Thus, the interpretation of quantum pressure holds in the bulk for AdS black hole, generalizing the previous result for the asymptotically flat black hole. We then show that the leading geometric correction comes from the third order in curvature and explicitly calculate the corrections to the metric and to the horizon. For applications to AdS/CFT, we conjectured a nonlocal Gibbons–Hawking–York boundary term along with the necessary counter terms to cancel the ultraviolet divergence of the bulk action. We then calculate the thermodynamic quantities in the bulk and discuss their properties.