General Relativity and Gravitation最新文献

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.

Let M be a locally rotationally symmetric spacetime, and (xi ^a) a conformal Killing vector for the metric on M, lying in the subspace spanned by the unit timelike direction and the preferred spatial direction, and with non-constant components. Under the assumption that the divergence of (xi ^a) has no critical point in M, we obtain the necessary and sufficient condition for (xi ^a) to generate a conformal Killing horizon. It is shown that (xi ^a) generates a conformal Killing horizon if and only if either of the components (which coincide on the horizon) is constant along its orbits. That is, a conformal Killing horizon can be realized as the set of critical points of the variation of the component(s) of the conformal Killing vector along its orbits. Using this result, a simple mechanism is provided by which to determine if an arbitrary vector in an expanding LRS spacetime is a conformal Killing vector that generates a conformal Killing horizon. In specializing the case for which (xi ^a) is a special conformal Killing vector, provided that the gradient of the divergence of (xi ^a) is non-null, it is shown that LRS spacetimes cannot admit a special conformal Killing vector field, thereby ruling out conformal Killing horizons generated by such vector fields.

The present paper deals with the Schwarzschild black holes with quintessence whose geometry is sourced by a magnetic monopole in the context of non-linear electrodynamics. After briefly discussing the timelike geodesics and radial motion, a special attention is given to the Dirac equation. In the massless case, the radial function is expressed in terms of Heun general functions. The outgoing wave solutions are used to compute the Hawking temperatures on the horizons and the corresponding heat capacities.

In this work, we study the first order corrections of Hawking temperature and entropy for modified Schwarzschild–Rindler black hole. To do so, we use the modified Lagrangian equation for vector particles in the background of quantum correction parameter (delta ). We examine the graphical interpretation of the corrected Hawking temperature with respect to horizon under the effects of correction parameter in order to verify the gravitational effects on the geometry of the modified Schwarzschild–Rindler black hole. We perform a graphic analysis of the modified Schwarzschild–Rindler black hole’s physical state as a function of the mass and Rindler acceleration under the effects of correction parameter. Moreover, we derive the corrected entropy and study the effects of mass and Rindler acceleration parameter on entropy under different variations of correction parameter.

Abstract

We study the power spectrum of the uniformly accelerating scalar field, obeying the (kappa ) -deformed Klein–Gordon equation. From this we obtain the (kappa ) -deformed corrections to the Unruh temperature, valid up to first order in the (kappa ) -deformation parameter a. We also show that in the small acceleration limit, this expression for the Unruh temperature in (kappa ) -deformed space-time is in exact agreement with the one derived from the (kappa ) -deformed uncertainty relation. Finally, we obtain an upper bound on the deformation parameter a.

Abstract

We investigate spherically symmetric static and dynamical Brans–Dicke theory exact solutions using invariants and, in particular, the Newman Penrose formalism utilizing Cartan scalars. In the family of static, spherically symmetric Brans–Dicke solutions, there exists a three-parameter family of solutions, which have a corresponding limit to general relativity. This limit is examined through the use of Cartan invariants via the Cartan–Karlhede algorithm and is additionally supported by analysis of scalar polynomial invariants. It is determined that the appearance of horizons in these spacetimes depends primarily on one of the parameters, n, of the family of solutions. In particular, expansion-free surfaces appear which, for a subset of parameter values, define additional surfaces distinct from the standard surfaces (e.g., apparent horizons) identified in previous work. The “ (r=2M) ” surface in static spherically symmetric Brans–Dicke solutions was previously shown to correspond to the Schwarzschild horizon in general relativity when an appropriate limit exists between the two theories. We show additionally that other geometrically defined horizons exist for these cases, and identify all solutions for which the corresponding general relativity limit is not a Schwarzschild one, yet still contains horizons. The identification of some of these other surfaces was noted in previous work and is characterized invariantly in this work. In the case of the family of dynamical Brans–Dicke solutions, we identify similar invariantly defined surfaces as in the static case and present an invariant characterization of their geometries. Through the analysis of the Cartan invariants, we determine which members of these families of solutions are locally equivalent, through the use of the Cartan–Karlhede algorithm. In addition, we identify black hole surfaces, naked singularities, and wormholes with the Cartan invariants. The aim of this work is to demonstrate the usefulness of Cartan invariants for describing properties of exact solutions like the local equivalence between apparently different solutions, and identifying special surfaces such as black hole horizons.