119231146
Asymptotically Flat Radiating Solutions in Third Order Lovelock Gravity
In this paper, we present an exact spherically symmetric solution of third order Lovelock gravity in n dimensions which describes the gravitational collapse of a null dust fluid. This solution is asymptotically (anti-)de Sitter or flat depending on the choice of the cosmological constant. Using the asymptotically flat solution for n{>=}7 with a power-law form of the mass as a function of the null coordinate, we present a model for a gravitational collapse in which a null dust fluid radially injects into an initially flat and empty region. It is found that a naked singularity is inevitably formed whose strength is different for the n=7 and n{>=}8 cases. In the n=7 case, the limiting focusing condition for the strength of curvature singularity is satisfied. But for n{>=}8, the strength of curvature singularity depends on the rate of increase of mass of the spacetime. These considerations show that the third order Lovelock term weakens the strength of the curvature singularity.
123162229
Generalized uncertainty principle, modified dispersion relation and Reissner–Nordström black hole tunneling radiation
Abstract The Parikh–Kraus–Wilczek tunneling proposal of black hole tunneling radiation is considered. Reissner–Nordstrom black hole thermodynamics is studied according to the generalized uncertainty principle and the modified dispersion relation analysis. It is shown that entropy, temperature and the original Parikh–Kraus–Wilczek calculation of the black hole tunneling probability receive new corrections. The results of these two alternative approaches are identical if one uses the suitable expansion coefficients.
119433688
Thermodynamics of rotating charged black strings and (A)dS / CFT correspondence
We use the anti\char21{}de Sitter (AdS) conformal field theory correspondence to calculate the conserved charges and the Euclidean actions of the charged rotating black string in four dimensions both in the canonical and the grand-canonical ensemble. The four-dimensional solution of the Einstein-Maxwell equations with a positive cosmological constant is introduced, and its conserved quantities and actions for fixed charge and fixed electric potential are calculated. We also study the thermodynamics of the asymptotically AdS black strings and perform a stability analysis both in the canonical and the grand-canonical ensembles. We find that the asymptotically AdS black string in the canonical ensemble is locally stable, while in the grand-canonical ensemble it is stable only for a part of the phase space.
120694400
Instanton effects on extracting the nucleon parton distributions
In considering the nucleon parton distributions at low energy values, the non-perturbative effects will have an important role. It is usual to assume for the related vacuum a structure and attribute it a back ground field. It is very like to the situation which we have for Bohm-Aharnov effect when an electron moved in a region where there is not any magnetic field (vacuum). In this case we can attribute to the related vacuum a back ground field which is in fact the gauge field of electrodynamics force. The fluctuations which exist with respect to the concerned vacuum in QCD can appear as instantons and will effect on then nucleon parton distributions especially at low Bjorken-x values. A comparison between the proton structures when we consider the instanton effect with respect to the usual one, indicates the non-perturbative effect on extracting these functions. Considering this effect will yield a better result for the F 2 p structure function.
123206943
Hawking Effect with Generalized Uncertainty Principle and Modified Dispersion Relations in de Sitter-Schwarzschild Black Hole
Although the tunneling approach is well established for black hole’s radiation, much works have been done to support the extension of this approach to more general settings. In This letter the Parikh-Kraus-Wilczek tunneling proposal of black hole’s tunneling radiation has been considered. The de Sitter-Schwarzschild black hole’s thermodynamics has been studied based on both, the generalized uncertainty principle and the modified dispersion relations analysis. It is shown that entropy, temperature and the original Parikh-Kraus-Wilczek calculations of the black hole’s tunneling probability receive new corrections. The results of these two alternative approaches are identical if one uses the suitable expansion coefficients.
119193740
Surface terms of quasitopological gravity and thermodynamics of charged rotating black branes
We introduce the surface term for quasitopological gravity in order to make the variational principle of the action well defined. We also introduce the charged black branes of quasitopological gravity and calculate the finite action through the use of the counterterm method. Then we compute the thermodynamic quantities of the black brane solution by use of Gibbs free energy and investigate the first law of thermodynamics by introducing a Smarr-type formula. Finally, we generalize our solutions to the case of rotating charged solutions.
118016384
Constraint structure and Hamiltonian treatment of Nappi-Witten model
We investigate the Hamiltonian analysis of Nappi-Witten model (WZW action based on non semi simple gauge group) and find a time dependent non-commutativity by canonical quantization. Our procedure is based on constraint analysis of the model in two parts. A first class analysis is used for gauge fixing the original model following by a second class analysis in which the boundary condition are treated as Dirac constraints. We find the reduced phase space by imposing our second class constraints on the variables in an extended Fourier space.
116202352
Simplifying the algebra of first class constraints, SO(3) as an example
1539587
Noncommutative Geometry and Classical Orbits of Particles in a Central Force Potential
We investigate the effect of the noncommutative geometry on the classical orbits of particles in a central force potential The relation is implemented through the modified commutation relations [xi,xj] = iθij. Comparison with observations places severe constraints on the value of the noncommutativity parameter.
11749680
The Decay of singlet scalar dark matter to unparticle and photon
We consider the unparticle physics introduced by Georgi and show that if the standard model is extended to include a singlet scalar as a dark matter candidate, there is a channel which leads to its decay to photon and unparticle. We calculate the decay rate for this new channel and find a lower bound on unparticle physics scale by demanding the stability of this candidate of the dark matter.