General Relativity and Gravitation最新文献

Abstract

Numerical Relativity has been of fundamental importance for studying compact binary coalescence dynamics, waveform modelling, and eventually for gravitational waves observations. As the sensitivity of the detector network improves, more precise template modelling will be necessary to guarantee a more accurate estimation of astrophysical parameters. To help improve the accuracy of numerical relativity catalogs, we developed a deep learning model capable of detecting anomalous waveforms. We analyzed 1341 binary black hole simulations from the SXS catalog with various mass-ratios and spins, considering waveform dominant and higher modes. In the set of waveform analyzed, we found and categorised seven types of anomalies appearing in the coalescence phases.

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 when the metric function associated to the fifth dimension is considered to be constant. The calculation of the geodesics allows to identify the existence or not of different behaviours of test particles, in orbits on a constant plane, between the two metrics. In addition, static solutions on the hypersurface orthogonal to the added dimension but with time dependence in the five-dimensional metric are also obtained. The consequences on the variation of the rest mass, if the fifth dimension is identified with it, are studied.

In this paper we study the global existence and completeness of classical solutions of gravity coupled a scalar field system called Einstein–Klein–Gordon system in higher dimensions. We introduce a new ansatz function to reduce the problem into a single first-order integro-differential equation. Then, we employ the contraction mapping in the appropriate Banach space. Using Banach fixed theorem, we show that there exists a unique fixed point, which is the solution of the theory. For a given initial data, we prove the existence of both local and global classical solutions. We also study the completeness properties of the spacetime. Here, we introduce a mass-like function for (Dge 4) in Bondi coordinates. The completeness of spacetime along the future directed timelike lines outward to a region which resembles the event horizon of the black hole.

In this paper, we construct the slowly rotating case of an asymptotically flat supermassive black hole embedded in dark matter using Newman–Janis procedure. Our analysis is carried with respect to the involved parameters including the halo total mass M and the galaxy’s lengthscale (a_0). Concretly, we investigate the dark matter impact on the effective potential and the photon sphere. In particular, we find that the lengthscale (a_0) controles such potential values. Indeed, for low (a_0) values, we find that the halo total mass M decreases the potential values significantly while for high (a_0) values such impact is diluted. Regarding the shadow aspects, we show that the shadow size is much smaller for high values of (a_0) while the opposite effect is observed when the halo total mass M is increased. By comparing our case to the slowly rotating case, we notice that the former exhibits a shadow shifted from its center to the left side. Finally, we compute the deflection angle in the weak-limit approximation and inspect the dark matter parameters influence. By ploting such quantity, we observe that one should expect lower bending angle values for black holes in galactic nuclei.

This work provides, at lower order, general analytical solutions for the orbital separation, merging time, and orbital frequency of binary systems emitting gravitational waves while being submitted to mass variations. Specific features, depending on the exponent of the mass derivative, are investigated in details. Two phenomenologically interesting cases are explicitly considered: (i) binaries formed by two light primordial black holes submitted to Hawking evaporation and (ii) bodies driven by a Bondi accretion of phantom dark energy. It is shown that three different regimes arise, including an intricate non-monotonic behaviour of the system. We study subtle imprints that could be associated with those phenomena. A careful analysis of the conditions of validity of the different hypotheses performed is finally carried out.

We show how the introduction of a rank two antisymmetric tensor within the construction of the spacetime contortion sets the geometric framework in which gravitation and electromagnetism can be formulated synthetically through a unique action of Hilbert type in four dimensions. In particular, free Maxwell’s equations are recovered as a consequence of the field equations in the limit of metrically flat spacetime.

This paper studies the Rindler trajectories in the Cloud of strings in 3rd-order Lovelock gravity. According to the generalization of the Letaw–Frenet equations for curved spacetime (ST), the trajectory will continue to accelerate linearly and uniformly throughout its motion. The ST of the Cloud of strings in 3rd-order Lovelock gravity, a boundary is established on the bound of the accelerated magnitude |a| for radially inward traveling trajectories in the expression of the BH mass m which is represented by (|a|le {frac{ left( b+1 right) ^{3/2}}{3 sqrt{3} m}}). For a certain selection of asymptotic initial data h, the linearly uniformly accelerated trajectory always enters the BH for acceleration |a| greater than the bound value. To study the bound value by |a|, the radial linearly uniformly accelerated trajectory can only travel to infinity within a small radius or the distance of the closest approach. However, it is observed that when the bound (|a| = {frac{ left( b+1 right) ^{3/2}}{3 sqrt{3} m}}) is saturated, and this distance approaches its lowest value of (r_b = {frac{3m}{b+1}}). We also demonstrate that the value of the acceleration has a limited constraint, there is always an extension of the closest approach (r_b > {frac{2m}{b+1}}) for (|a|le B(m, h)), for each set of finite asymptotic initial data h.

In this work, we consider the effects of repulsive gravity in an invariant way for four static 3D regular black holes, using the eigenvalues of the Riemann curvature tensor, the Ricci scalar, and the strong energy conditions. The eigenvalues of the solutions are non-vanishing asymptotically (in asymptotically AdS) and increase as the source of gravity is approached, providing a radius at which the passage from attractive to repulsive gravity might occur. We compute the onsets and the regions of repulsive gravity and conclude that the regular behavior of the solutions at the origin of coordinates can be interpreted as due to the presence of repulsive gravity, which also turns out to be related with the violation of the strong energy condition. We showed that in all of the solutions for the allowed region of parameters, gravity changes its sign, but the repulsive regions only for the non-logarithmic solution are affected by the mass that generates the regular black hole. The repulsive regions for the logarithmic solutions are dependent on electric charge and the AdS(_{3}) length. The implications and physical consequences of these results are discussed in detail.

The stability of Reissner–Nördstrom black holes with an extremal mass–charge relation was determined by calculating the propagation speed of gravitational waves on this background in an effective field theory (EFT) of gravity. New results for metric components are shown, along with the corresponding new extremal relation, part of which differs by a global factor of 2 from the past published work. This new relation further develops the existing constraints on EFT parameters. The radial propagation speed for gravitational waves in the Regge–Wheeler gauge was calculated linearly for all perturbations, yielding exact luminality for all dimension-4 operators. The dimension-6 radial speed modifications introduce no constraints on the sign of the modified theory parameters from causality arguments, while the deviation from classical theories vanishes at both horizons. The angular speed was found to be altered for the dimension-4 operators, with possible new constraints on the modified theory being suggested from causality arguments. Results are consistent with existing literature on Schwarzschild black hole backgrounds, with some EFT terms becoming active only in non-vacuum spacetimes such as Reissner–Nördstrom black holes.