International Journal of Modern Physics D

The behavior of a charged scalar field in the RN black hole space–time is studied using the WKB approximation. In the present work, it is assumed that matter waves can be reflected from the event horizon. Using this effect, the Hawking temperature and the absorption cross section for an RN black hole placed in a charged scalar field are calculated. The absorption cross section σ_abs is found to be inversely proportional to the square of the Hawking temperature of the black hole.

We investigate the properties of space–times resulting from matching together exact solutions using the Darmois matching conditions. In particular, we focus on the asymptotically velocity-term dominated property (AVTD). We propose a criterion that can be used to test if a space–time constructed from a matching can be considered AVTD. Using the "cheese slice" universe as an example, we show that a space–time constructed from a such a matching can inherit the AVTD property from the original space–times. Furthermore the singularity resulting from this particular matching is an AVTD singularity.

We examine the (n + 1)-dimensional (n ≥ 3) action in which gravity is coupled to the Born–Infeld nonlinear electrodynamic and a dilaton field. We construct a new (n + 1)-dimensional analytic solution of this theory in the presence of Liouville-type dilaton potentials. These solutions, which describe charged topological dilaton black holes with nonlinear electrodynamics, have unusual asymptotics. They are neither asymptotically flat nor (anti)-de Sitter. The event horizons of these black holes can be an (n - 1)-dimensional positive, zero or negative constant curvature hypersurface. We also analyze the thermodynamics and stability of these solutions and disclose the effect of the dilaton and Born–Infeld fields on the thermal stability in the canonical ensemble.

The cosmological dynamics of a minimally coupled scalar field that couples to the background matter with thermal interactions is investigated using statefinder diagnostics. The time evolution of the statefinder pairs {r, s} and {r, q} are obtained under the circumstance that different values of model parameters are chosen. We show that the thermal coupling term does not affect the location of the late-time attractor, but exerts an influence on the evolution of the statefinder parameters. The most notable feature of the r–s plane for the thermal coupling model, which is distinguished from the other dark energy models, is that some part of the curve with thermal coupling can form a closed loop in the second quadrant (r > 1, s < 0).

In this paper, we analyze the effect produced by the temperature in the vacuum polarization associated with a charged massless scalar field in the presence of a magnetic flux tube in the cosmic string space–time. Three different configurations of magnetic fields are taken into account: (i) a homogeneous field inside the tube, (ii) a field proportional to 1/r, and (iii) a cylindrical shell with δ-function. In these three cases, the axis of the infinitely long tube of radius R coincides with the cosmic string. Because of the complexity of this analysis in the region inside the tube, we consider the thermal effect in the region outside. In order to develop this analysis, we construct the thermal Green function associated with this system for the three above-mentioned situations considering points in the region outside the tube. We explicitly calculate, in the high-temperature limit, the thermal average of the field square and the energy–momentum tensor.

In this paper, conformal motions are studied in plane symmetric static space–times. The general solution of conformal Killing equations and the general form of the conformal Killing vector for these space–times are presented. All possibilities for the existence of conformal motions in these space–times are exhausted.

We shall show that it is possible to make a causal interpretation of loop quantum cosmology using the momentum as the dynamical variable. We shall show that one can derive Bohmian trajectories. For a sample cosmological solution with cosmological constant, the trajectory is plotted.

In this paper, we develop and apply the WKB-type approximation to several examples of noncommutative quantum cosmology, obtaining the time evolution of the noncommutative universe. This is accomplished by starting from a noncommutative quantum formulation of cosmology, where the noncommutativity is introduced by a deformation on the minisuperspace variables. This procedure gives a straightforward algorithm to incorporate noncommutativity into cosmology and inflation.

General relativistic quantum interference effects in a slowly rotating NUT space–time, such as the Sagnac effect and the phase shift effect of interfering particles in a neutron interferometer, are considered. It was found that in the case of the Sagnac effect, the influence of the NUT parameter is becoming important due to the fact that the angular velocity of the locally nonrotating observer must be larger than the one in the Kerr space–time. In the case of neutron interferometry, it is found that due to the presence of the NUT parameter, an additional term in the phase shift of interfering particles emerges. This term can be, in principle, detected by a sensitive interferometer and the derived results could be further used in experiments to detect the gravitomagnetic charge. Finally, as an example, we apply the obtained results to the calculation of the UCN (ultra-cold neutrons) energy level modification in a slowly rotating NUT space–time.

We derive the cosmic energy equation for extended mass structures (i.e., galaxies with halos) which cluster gravitationally in the expanding universe. From this cosmic energy equation, we study the quasi-static evolution for nonpoint mass system of galaxies. Using this cosmic energy equation, we examine the growth of correlation potential energy for the extended masses. We also derive the expression for virial mass and try to account for the dark matter present in the halos of the galaxies.

The Misner and Sharp approach to the study of gravitational collapse is extended to the viscous dissipative case in both the streaming out and the diffusion approximations. The dynamical equation is then coupled to causal transport equations for the heat flux, the shear, and the bulk viscosity, in the context of Israel–Stewart theory, without excluding the thermodynamics viscous/heat coupling coefficients. The result is compared with previous works where these later coefficients were neglected and viscosity variables were not assumed to satisfy causal transport equations. Prospective applications of this result to some astrophysical scenarios are discussed.

Motivated by the recent observations for cosmic acceleration and the suitable evolution of the universe provided an interaction (decay of dark energy to matter) is incorporated in a cosmological model, we study the cosmological evolution of the interacting holographic dark energy scenario. Critical points are derived and their corresponding cosmological models are presented. The dynamical character of these models is revealed.

We study the effects of noncommutativity of space–time geometry on the thermodynamical properties of the de Sitter horizon. We show that noncommutativity results in modifications in temperature, entropy and vacuum energy and that these modifications are of order of the Planck scale, suggesting that the size of the noncommutative parameter should be close to that of the Planck. In an alternative way to deal with noncommutativity, we obtain a quantization rule for the entropy. Since noncommutativity in space–time geometry modifies the Heisenberg algebra and introduces the general uncertainty principle, we also investigate the above problem in this framework.