This paper formulates, via the Mathisson - Papapetrou - Dixon equations, the system of equations for a test particle with spin when it is orbiting a weak Kerr metric. We shall restrict ourselves to the case of circular orbits with the purpose of comparing our results with the results of the literature. In particular, we solve the set of equations of motion for the case of circular trajectories both spinless and spinning test particles around rotating bodies in equatorial plane. The results obtained are an important guideline for the study of the effects of the particles with spin in rotating gravitational fields such as Gravitomagnetics Effects or gravitational waves.
Sep 09 2014 gr-qc
Since the development of Relativity theory, a variety of solutions have been found around Einstein field equations, depending on the time-space. For instance, we can find the axially symmetric space which describes a rotanting black hole. To understand this astrophysics objects, we must do a ray tracing, which is a simulation of photon's trajectory from the black hole to observer. Since are millions of photons recievied by the observer, we need a computational tool to resolve this problem for generating the image of black hole. Thanks to the YNOGK- GEOKERR code, we can visualise the black holes characteristics and the solutions of the equations of motion using separability and interior point methods. With this article we want to study this type of space and also to show the results for black hole simulations with this routine.
Feb 14 2014 gr-qc
In the context of metric $f(R)$ gravity, the Geodesic Deviation Equation (GDE) was first studied in arXiv:1010.5279v3, giving a general expression and studying a particular case, the FLRW universe. In the paper arXiv:1312.2022v1 a similar analysis was made. However, there is a discrepancy in the expressions for the null vector field case due to an algebraic error in our original paper. Here, we make explicit the contribution of the different operators in the GDE, and we correct our previous results.
We present a coherent account of how the entanglement interpretation, thermofield dynamical description and the brick wall formulations (with the ground state correctly identified) fit into a connected and self-consistent explanation of what Bekenstein-Hawking entropy is, and where it is located.
The origin of galactic and extra-galactic magnetic fields is an unsolved problem in modern cosmology. A possible scenario comes from the idea of these fields emerged from a small field, a seed, which was produced in the early universe (phase transitions, inflation, ...) and it evolves in time. Cosmological perturbation theory offers a natural way to study the evolution of primordial magnetic fields. The dynamics for this field in the cosmological context is described by a cosmic dynamo like equation, through the dynamo term. In this paper we get the perturbed Maxwell's equations and compute the energy momentum tensor to second order in perturbation theory in terms of gauge invariant quantities. Two possible scenarios are discussed, first we consider a FLRW background without magnetic field and we study the perturbation theory introducing the magnetic field as a perturbation. The second scenario, we consider a magnetized FLRW and build up the perturbation theory from this background. We compare the cosmological dynamo like equation in both scenarios.
In this paper we study the Geodesic Deviation Equation (GDE) in metric f(R) gravity. We start giving a brief introduction of the GDE in General Relativity in the case of the standard cosmology. Next we generalize the GDE for metric f(R) gravity using again the FLRW metric. A generalization of the Mattig relation is also obtained. Finally we give and equivalent expression to the Dyer-Roeder equation in General Relativity in the context of f(R) gravity.
We find a new charged black hole in three-dimensional anti-de Sitter space using an anisotropic perfect fluid inspired by the noncommutative black hole as the source of matter and a gaussian distribution of electric charge. We deduce the thermodynamical quantities of this black hole and compare them with those of a charged BTZ solution.
We find a new rotating black hole in three-dimensional anti-de Sitter space using an anisotropic perfect fluid inspired by the noncommutative black hole. We deduce the thermodynamical quantities of this black hole and compare them with those of a rotating BTZ solution.
Mar 19 2010 gr-qc
We present the exact equation for evolution of Bianchi I cosmological model, considering a non-tilted perfect fluid in a matter dominated universe. We use the definition of shear tensor and later we prove it is consistent with the evolution equation for shear tensor obtained from Ricci identities and widely known in literature , , . Our result is compared with the equation given by Ellis and van Elst in  and Tsagas, Challinor and Maartens . We consider that it is important to clarify the notation used in ,  related with the covariant derivative and the behavior of the shear tensor.
The main goal of this paper is to get in a straightforward form the field equations in metric f(R) gravity, using elementary variational principles and adding a boundary term in the action, instead of the usual treatment in an equivalent scalar-tensor approach. We start with a brief review of the Einstein-Hilbert action, together with the Gibbons-York-Hawking boundary term, which is mentioned in some literature, but is generally missing. Next we present in detail the field equations in metric f(R) gravity, including the discussion about boundaries, and we compare with the Gibbons-York-Hawking term in General Relativity. We notice that this boundary term is necessary in order to have a well defined extremal action principle under metric variation.
Jun 26 2009 gr-qc
In a recent propposal, the cosmological constant has been considered as as a new thermodynamical variable and its change is related to the radiation produced by black holes. Using this consideration and by modelling the primordial black holes as Schwarzschild-de Sitter holes,we have constrained the total mass of primordial black holes evaporated by now, giving an estimate of the order of 1.624x10^24 solar masses.
May 13 2005 gr-qc
Natural wormholes and its astrophysical signatures have been sugested in various oportunities. By applying the strong field limit of gravitational lensing theory, we calculate the deflection angle and magnification curves produced by Morris-Thorne wormholes in asimptotically flat space-times. The results show that wormholes act like convergent lenses. Therefore, we show that it is hard to distinguish them from black holes using the deflection's angle of the gravitational lens effect, in contrast with the results reported by Cramer et.al. and Safanova et.al. However, we also show that it is possible, in principle, distinguish them by the magnification curves, in particular, by observing the position of the peak of the Einstein's ring.