General Relativity and Gravitation最新文献

Correction to: Geometrical Origin of the Cosmological Constant, Gen. Relativ. Gravit. 44, 2547-2561 (2012). https://doi.org/10.1007/s10714-012-1413-9

In this study, we consider FRW universe filled with matter, non-minimally coupling (NMC) scalar field under (V(phi ) = V_{0}phi ^{2}) potential and holographic vacuum energy. Dark energy is contributed from both holographic vacuum energy and the NMC scalar field. NMC effective gravitational constant (G_text {eff}(phi )), is naturally defined at the action level. Therefore, the gravitational constant in the holographic vacuum density is an effective one, i.e. ( rho _{Lambda } = {3c^{2}}/{8pi G_{text {eff}}L^{2}},. ) Apparent horizon is chosen as IR holographic cutoff scale as it is a trapped null surface. There are nine fixed points in this dynamical system with four independent dimensionless parameters. We consider flat case and find that viable cosmological evolution follows the sequence: an initial stiff-fluid-dominated phase, transitioning through a nearly dust-dominated era, and eventually reaching a stable dark energy-dominating state. Stability analysis requires that (xi <0) and (0< c < 1) for the theory to be physically valid. Since zero NMC coupling, (xi =0), is not allowed in the autonomous system, the model can not completely recover canonical scalar field case. That is to say, as (xi rightarrow 0^-) and (c rightarrow 0^+), the model can only approach the canonical scalar case but can not completely recover it. To approach dust or stiff fluid dominations, both magnitudes of the NMC coupling and the holographic parameter must be small. Numerical integration shows that for any allowed values of (xi ) and c, (w_text {eff}) approaches (-1) at late times. Increasing of c does not change shape of the (w_textrm{eff}), but larger c increases (w_text {eff}). As (xi ) becomes stronger, dust era gradually disappears. Good behaviors of the dynamics require (-1 ll xi <0) and (0 < c ll 1).

The aim of this paper is to study the historical roots of Lemaître’s famous Primeval Atom Hypothesis (PAH) which are in fact not at all unique. We show that the PAH was linked to his early interests in quantum themes and concepts (Heisenberg uncertainty relations, Eddington-Dirac spinors, etc.) which he studied around 1930, but also to his researches on singularities in General Relativity and above all to this passion for Cosmic Rays, which stimulated his thought in Physics (Celestial Mechanics, for example) but also in Mathematics (numerical analysis, computing science, etc.) The second aim of this paper is to understand the epistemological status of this hypothesis. This status as well as the meaning of the Primeval Atom was evolving during Lemaître’s life. The PAH was never precisely described mathematically in the field of cosmology but acted as a cosmogonical image, generating many fruitful intuitions and stimulating many technical researches.

The long-time evolution of extreme mass-ratio inspiral systems requires minimal phase and dispersion errors to accurately compute far-field waveforms, while high accuracy is essential near the smaller black hole (modeled as a Dirac delta distribution) for self-force computations. Spectrally accurate methods, such as nodal discontinuous Galerkin (DG) methods, are well suited for these tasks. Their numerical errors typically decrease as (propto (Delta x)^{N+1}), where (Delta x) is the subdomain size and (N) is the polynomial degree of the approximation. However, certain DG schemes exhibit superconvergence, where truncation, phase, and dispersion errors can decrease as fast as (propto (Delta x)^{2N+1}). Superconvergent numerical solvers are, by construction, extremely efficient and accurate. We theoretically demonstrate that our DG scheme for the scalar Teukolsky equation with a distributional source is superconvergent, and this property is retained when combined with the hyperboloidal layer compactification technique. This ensures that waveforms, total energy and angular-momentum fluxes, and self-force computations benefit from superconvergence. We empirically verify this behavior across a family of hyperboloidal layer compactifications with varying degrees of smoothness. Additionally, we show that dissipative self-force quantities for circular orbits, computed at the point particle’s location, also exhibit a certain degree of superconvergence. Our results underscore the potential benefits of numerical superconvergence for efficient and accurate gravitational waveform simulations based on DG methods.

We investigate the thermodynamics of asymptotically Anti-de Sitter charged and rotating black strings in extended phase space, in which the cosmological constant is interpreted as thermodynamic pressure and the thermodynamic volume is defined as its conjugate. We find the thermodynamic volume, the internal energy, and the Smarr law. We study the thermal stability and show that some of the solutions have positive specific heat, which makes them thermodynamically stable. We find, for the first time, there is a critical point for charged solutions which occurs at the point of divergence of specific heat at constant pressure. This supports the existence of a second-order phase transition analogous to the liquid-gas critical point in Van der Waals fluids. We also study the maximal efficiency of a Penrose process and find that an extremal rotating black string can have an efficiency of up to 50%. We also find the equation of state for uncharged solutions. By comparing with the liquid-gas system, we observe that there is not a critical behavior to coincide with those of the Van der Waals system.

In this paper, we studied quantum tunneling of massless and massive particles pertaining to a Schwarzschild black hole in a quintessence background, and explored the consequences emerging from a generalized uncertainty principle (GUP). For the quintessence scenario, we considered two specific cases of w, which is the ratio of the pressure and energy density, namely (w=-1/3) and (w=-2/3). For the GUP, we used a modified Schwarzschild metric and employed a unique choice of contour integration to compute the tunneling amplitudes. An analysis and comparative study of the respective temperature profiles has been made. The energy emission rate has also been analysed.

The one-loop quantum corrections of General Relativity contribute to understand its ultraviolet completion and can be tested by directly imaging the supermassive black hole in our Galactic center. In this work, we analytically investigate the weak deflection gravitational lensing of the one-loop quantum corrected Schwarzschild spacetime that is characterized by a normalized quantum correction parameter (lambda ), and discuss the detectability of its weak deflection lensing observables. We find that these observables have the potential to be measured but their deviations from those of a Schwarzschild black hole can not be distinguished due to current limited resolution. To gain deeper insights into the quantum nature, we further study the strong deflection gravitational lensing analytically. According to the shadow measurement of Sgr A* by the Event Horizon Telescope, we obtain a constraint on (lambda ) and demonstrate that the strong deflection lensing observables such as the angular separation, brightness difference and time delay of the relativistic images are beyond the reach of present capacity in this allowable range. Consequently, identifying the quantum effects around such a corrected Schwarzschild spacetime with gravitational lensing is not feasible at current stage.

We briefly overview the case for using black holes as a discriminator for theories of gravity. The opportunities and challenges for the various observational experiments are outlined, and key questions for the community identified. This note summarises the discussion from the roundtable on the third day of Black Holes Inside and Out.

We investigate the evolution of anisotropies in Einstein-Gauss-Bonnet theory with a scalar field coupled to the Gauss-Bonnet term. Specifically, we examine the simplest scenario in which the scalar field lacks a kinetic term, and its kinetic contribution arises from an integration by parts of the Gauss-Bonnet scalar. We consider four- and five-dimensional anisotropic spacetimes, focusing on Bianchi I and extended Bianchi I geometries. Our study reveals that the asymptotic solutions correspond to locally symmetric spacetimes where at least two scale factors exhibit analogous behavior or, alternatively, to isotropic configurations where all scale factors evolve identically. Additionally, we discuss the effects of a cosmological constant, finding that the presence of the cosmological constant does not lead to an isotropic universe.