General Relativity and Gravitation最新文献

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.

We are entering the era of precision black hole astronomy. Thanks to gravitational wave interferometers like LIGO-Virgo-KAGRA and potential first-generation space-based detectors like LISA, the next few decades will provide direct gravitational probes of supermassive black holes at horizon scales. However, gravitational wave detectors are not alone. Thanks to the unprecedented resolution of very-long-baseline interferometry (VLBI) instruments like the Event Horizon Telescope and potential space extensions like the Black Hole Explorer, black hole horizon-scale features (e.g., the photon sphere and inner shadow) are expected to come into focus within the next decade. In this letter, we will highlight the potential for precision measurements of black holes using VLBI and how it can provide an independent probe of these objects.

We derive the metric of a circular chiral vorton in the weak field limit. The object is self-supporting by means of its chiral current. A conical singularity with deficit angle, identical to that of straight string with the same linear mass density, is present at the vorton’s core. We find that the metric is akin to the electromagnetic 4-potential of a circular current wire loop, illustrating the concept of gravito-electromagnetism. Surprisingly we find that the solution asymptotically mimics a Kerr-like naked singularity with mass (M_v=4pi Rmu ) and spin parameter (a=R/2). Finally, we also simulate the gravitational lensing images by solving the corresponding null geodesic equations. This reveals interesting properties of the images, such as the simultaneous creation of a minimally distorted source image and its Einstein ring, as well as the formation of double images on the back side of the ring.

Andersson and Chruściel showed that generic asymptotically hyperboloidal initial data sets admit polyhomogeneous expansions, and that only a non-generic subclass of solutions of the conformal constraint equations is free of logarithmic singularities. The purpose of this work is twofold. First, within the evolutionary framework of the constraint equations, we show that the existence of a well-defined Bondi mass brings the asymptotically hyperboloidal initial data sets into a subclass whose Cauchy development guaranteed to admit a smooth boundary, by virtue of the results of Andersson and Chruściel. Second, by generalizing a recent result of Beyer and Ritchie, we show that the existence of well-defined Bondi mass and angular momentum, together with some mild restrictions on the free data, implies that the generic solutions of the parabolic-hyperbolic form of the constraint equations are completely free of logarithmic singularities. We also provide numerical evidence to show that in the vicinity of Kerr, asymptotically hyperboloidal initial data without logarithmic singularities can indeed be constructed.