General Relativity and Gravitation最新文献

This "vision document" is about what the future has in store for tests of general relativity with gravitational wave detectors. I will make an honest attempt to answer this question by addressing the role of inspiral-based and ringdown-based tests; recent progress on quasinormal modes in modified theories of gravity; the complementarity between light ring tests and ringdown tests; and the interesting possibility of observing some of the nonlinear effects predicted by general relativity. I may well prove to be wrong. To quote Yogi Berra: "It’s hard to make predictions, especially about the future".

Event horizons and Cauchy horizons are highly idealized mathematical constructions that do not fully capture the key physics of either Hawking radiation or mass inflation. Indeed, because they are teleological, both event horizons and Cauchy horizons are (in a precise technical sense) not physically observable. In contrast, by inspecting the quasi-local behaviour of null geodesics, long-lived apparent horizons (or more generally long-lived quasi-local horizons) are in principle physically observable, and are “good enough" for then pragmatically redefining a black hole, and “good enough” for generating Hawking radiation. Furthermore it is now also clear that long lived apparent horizons (quasi-local horizons) are also “good enough" for generating mass inflation. These observations suggest that one should be somewhat careful when trying to extrapolate rigorous mathematical theorems, which often embody mathematical idealizations that do not necessarily correspond to what a finite resource astronomer can actually measure, into the astrophysical realm.

Recent conjectures on the complexity of black holes suggest that their evolution manifests in the structural properties of Einstein-Rosen bridges, like the length and volume. The complexity of black holes relates to the computational complexity of their dual, namely holographic, quantum systems identified via the Gauge/Gravity duality framework. Interestingly, the latter allows us to study the evolution of a black hole as the transformation of a qubit collection performed through a quantum circuit. In this work, we focus on the complexity of Einstein-Rosen bridges. More in detail, we start with a preliminary discussion about their computational properties, and then we aim to assess whether an Ising-like model could represent their holographic dual. In this regard, we recall that the Ising model captures essential aspects of complex phenomena such as phase transitions and, in general, is deeply related to information processing systems. To perform this assessment, which relies on a heuristic model, we attempt to describe the dynamics of information relating to an Einstein-Rosen bridge encoded in a holographic screen in terms of dynamics occurring in a spin lattice at low temperatures. We conclude by discussing our observations and related implications.

Hawking’s seminal work on black hole radiation highlights a critical issue in our understanding of quantum field theory in curved spacetime (QFTCS), specifically the problem of unitarity loss (where pure states evolve into mixed states). In this paper, we examine a recent proposal for a direct-sum QFTCS, which maintains unitarity through a novel quantization method that employs geometric superselection rules based on discrete spacetime transformations. This approach describes a quantum state in terms of components that evolve within geometric superselection sectors of the complete Hilbert space, adhering to the discrete symmetries of a Schwarzschild black hole. Consequently, it represents a maximally entangled pure state as a direct-sum of two components in the interior and exterior regions of the black hole, thereby preserving the unitarity of Hawking radiation by keeping it in the form of pure states.

We construct a new class of ((n+1))-dimensional Lifshitz dilaton black brane solutions in the presence of the cubic quasitopological gravity for a flat boundary. The related action supports asymptotically Lifshitz solutions by applying some conditions which are used throughout the paper. We have to add a new boundary term and some new counterterms to the bulk action to have finite solutions. Then we define a finite stress tensor complex by which we can calculate the energy density of the quasitopological Lifshitz dilaton black brane. It is not possible to obtain analytical solutions, and so we use some expansions to probe -the behaviors of the functions, both near the horizon and, at the infinity. Combining the equations, we can attain a total constant along the coordinate r. At the horizon, this constant is proportional to the product of the temperature and the entropy and at the infinity, the total constant shows the energydensity of the quasitopological Lifshitz dilaton black brane. Therefore, we can reach a relation between the conserved quantities temperature, entropy and the energy density and get a smarr-type formula. Using the first law of thermodynamics, we can find a relation between the entropy and the temperature and then obtain the heat capacity. Our results show that the quasitopological Lifshitz dilaton black brane solutions are thermally stable for each positive value of the dynamical critiacl exponent, z.

We study zero and finite temperature static Bose-Einstein condensate (BEC) stars in the combined Rastall-Rainbow (RR) theory of gravity by considering different BEC equation of states (EoSs). We obtain the global properties of BEC stars by solving the modified Tolman-Oppenheimer-Volkoff equations of RR gravity with values of Rastall parameter (kappa ) and Rainbow function (Sigma ) chosen accordingly. We observe that the parameter (kappa ) has negligible effect on the maximum mass of the stars considered, whereas (Sigma ) alters it significantly, and increasing the value of (kappa ) beyond a certain limit results in unstable solutions for any value of (Sigma ). We report that the inclusion of temperature in our analysis expands the parameter space by including more values of (kappa ). However, temperature has negligible effect on the maximum mass of the stellar profiles in all the three theories. We have also studied the compactness and stability of the obtained stellar equilibria. We report that BEC stars satisfy various energy conditions within the range of (kappa ) and (Sigma ) taken in our paper. Further, we find that the maximum masses and radii of the stars within RR theory can have good agreement with the observational data on pulsars for all the EoSs considered and in particular, the Colpi-Wasserman-Shapiro EoS, which was ruled out in General Relativity (GR). We also find that, in contrast to the results of GR, BEC stars consistent with observations can be realised in the RR theory with smaller bosonic self-interaction strength.

This paper investigates the Joule-Thomson expansion for a five-dimensional neutral Gauss-Bonnet Anti-de Sitter black hole. Firstly, by taking Van der Waals gas as an example, we induce the definition of the Joule-Thomson coefficient and the inversion phenomena. One can give the T–P graph and the inversion curves. Then, we obtain the thermodynamic properties of the Gauss-Bonnet black hole and use the same way to get the T–P figure, which shows differences from Van der Waals gas and other black holes. To our surprise, we can’t observe its inversion phenomena. Due to this reason, we further studied the vanished inversion region and found that the electric charge plays an important role in this phenomenon. We analogy black hole charged and neutral, which get some interesting consequences. Finally, we make Legendre transition to Smarr relation and investigate whether the electric potential has the same result as the electric charge’s landscape. These results will uncover the inner interaction between the enthalpy and the electric charge during the Joule-Thomson process.

Quantum gravity has been baffling the theoretical physicist for decades now, both for its mathematical obscurity and phenomenological testing. Nevertheless, the new era of precision cosmology presents a promising avenue to test the effects of quantum gravity. In this study, we consider a bottom-up approach. Without resorting to any candidate quantum gravity, we invoke a generalized uncertainty principle (GUP) directly into the cosmological Hamiltonian for a universe sourced by a phantom scalar field with potential to study the evolution of the universe in a very early epoch. This is followed by a systematic analysis of the dynamics, both qualitatively and quantitatively. Our qualitative analysis shows that the introduction of GUP significantly alters the existence of fixed points for the potential considered in this paper. In addition, we confirm the existence of an inflationary phase and analyze the behavior of relevant cosmological parameters with respect to the strength of the GUP distortion.

We consider a homogeneous and isotropic spacetime having a space of positive curvature and study the cosmic evolution of dynamical vacuum energy. We utilize the dynamical system technique to study the existence of fixed points and their corresponding stability in model. The corresponding cosmological solutions describe late-time accelerating universe having decelerating era composed of radiation and matter-dominated phase. The numerical integration of autonomous system reveals that the cosmological solutions of dynamical vacuum energy model may describe the cosmic history of universe. As a consequence of the dynamical vacuum energy in closed Friedmann-Robertson-Walker model, the trajectories between fixed points in the phase space would also correspond to the bouncing and turnaround universe evolution.

Machine learning, particularly neural networks, has rapidly permeated most activities and work where data has a story to tell. Recently, deep learning has started to be used for solving differential equations with input from physics, also known as Physics-Informed Neural Network (PINNs). Physics-Informed Neural Networks (PINNs) applications in numerical relativity remain mostly unexplored. To remedy this situation, we present the first study of applying PINNs to solve in the time domain the Zerilli and the Regge-Wheeler equations for Schwarzschild black hole perturbations. The fundamental difference of our work with other PINN studies in black hole perturbations is that, instead of working in the frequency domain, we solve the equations in the time domain, an approach commonly used in numerical relativity to study initial value problems. To evaluate the accuracy of PINNs results, we compare the extracted quasi-normal modes with those obtained with finite difference methods. For comparable grid setups, the PINN results are similar to those from finite difference methods and differ from those obtained in the frequency domain by a few percent. As with other applications of PINNs for solving partial differential equations, the efficiency of neural networks over other methods emerges when applied to large dimensionality or high complexity problems. Our results support the viability of PINNs in numerical relativity, but more work is needed to assess their performance in problems such as the collision of compact objects.