International Journal of Modern Physics D

In this paper, we investigate the wave properties of cold plasma in the vicinity of Schawarzchild–de Sitter black hole horizon using 3 + 1 formalism. The general relativistic magnetohydrodynamical equations are formulated for this space–time with the use of Rindler coordinates. We consider both the rotating and nonrotating surroundings with magnetized and nonmagnetized plasmas. Linear perturbation and Fourier analysis techniques are applied by introducing simple harmonic waves. We derive complex dispersion relation from the determinant of Fourier analyzed equations for each case which provides real and complex values of the wave number. From the wave number we determine the phase and group velocities, the refractive index etc., which are used to discuss the characteristics of the waves around the event horizon.

It is shown that the rate of corrections to the hydrogen atom and harmonic oscillator energy levels due to the profound quantum gravitational effect of space–time dimension running/reduction coincides well with those obtained by means of minimum-length-deformed quantum mechanics. The rate of corrections is pretty much the same within the accuracy with which we can judge the quantum gravitational corrections at all. Such a convergence of results makes the concept of space–time dimension running more appreciable. As a remarkable distinction, the energy shift due to dimension reduction has the opposite sign as compared with the correction obtained by means of minimum-length-modified quantum mechanics. Therefore, the sign of total quantum gravitational correction remains somewhat obscure.

It is shown that the BSSN formulation of the Einstein equations, which forms the basis of most simulations in numerical relativity, explicitly uses the momentum constraints to evolve the conformal connection coefficients.

We study Hawking-like radiation in a Friedmann–Robertson–Walker (FRW) universe using the quasi-classical WKB/tunneling method, which pictures this process as a "tunneling" of particles from behind the apparent horizon. The correct temperature of the Hawking-like radiation from the FRW space–time is obtained using a canonical invariant tunneling amplitude. In contrast to the usual quantum-mechanical WKB/tunneling problem, where the tunneling amplitude has only a spatial contribution, we find that the tunneling amplitude for FRW space–time (i.e. the imaginary part of the action) has both spatial and temporal contributions. In addition we study backreaction and energy conservation of the radiated particles and find that the tunneling probability and the change in entropy, , are related by the relationship , which differs from the standard result, . By regarding the whole FRW universe as an isolated adiabatic system, the change in the total entropy is zero. Then, splitting the entropy between the interior and exterior parts of the horizon , we can explain the origin of the minus sign difference with the usual result: our is for the interior region, while the standard result from black hole physics is for the exterior region.

We show that for an RSII braneworld filled with interacting viscous dark energy and dark matter, one can always rewrite the Friedmann equation in the form of the first law of thermodynamics, dE = T_hdS_h + WdV, at the apparent horizon. In addition, the generalized second law of thermodynamics can be fulfilled in a region enclosed by the apparent horizon on the brane for both constant and time-variable five-dimensional Newton's constant G₅. These results hold regardless of the specific form of the dark energy. Our study further supports the belief that in an accelerating universe with spatial curvature, the apparent horizon is a physical boundary from the thermodynamical point of view.

We describe a new code to search for signatures of cosmic strings in cosmic microwave anisotropy maps. The code implements the Canny algorithm, an edge detection algorithm designed to search for the lines of large gradients in maps. Such a gradient signature which is coherent in position-space is produced by cosmic strings via the Kaiser–Stebbins effect. We test the power of our new code to set limits on the tension of the cosmic strings by analyzing simulated data, with and without cosmic strings. We compare maps with a pure Gaussian scale-invariant power spectrum with maps which have a contribution of a distribution of cosmic strings obeying a scaling solution. The maps have angular scale and angular resolution comparable to what current and future ground-based small-scale cosmic microwave anisotropy experiments will achieve. We present tests of the codes, indicate the limits on the string tension which could be set with the current code, and describe various ways to refine the analysis. Our results indicate that when applied to the data of ongoing cosmic microwave experiments such as the South Pole Telescope project, the sensitivity of our method to the presence of cosmic strings will be more than an order of magnitude better than the limits from existing analyses.

We construct a holographic dark energy model in a braneworld setup where gravity is induced on the brane embedded in a bulk with the Gauss–Bonnet curvature term. We include possible modifications of the induced gravity and its coupling with a canonical scalar field on the brane. Through a perturbational approach to calculating the effective gravitation constant on the brane, we examine the outcome of this model as a candidate for holographic dark energy.