Configurational entropy of charged AdS black holes

When we consider charged AdS black holes in higher dimensional spacetime and a molecule number density along coexistence curves is numerically extended to higher dimensional cases. It is found that a number density difference of a small and large black holes decrease as a total dimension grows up. In particular, we find that a configurational entropy is a concave function of a reduced temperature and reaches a maximum value at a critical (second-order phase transition) point. Furthermore, the bigger a total dimension becomes, the more concave function in a configurational entropy while the more convex function in a reduced pressure.Comment: 6 pages, 4 figures, typos corrected, version to appear in PL

The Extended Thermodynamic Properties of a topological Taub-NUT/Bolt-AdS spaces

We consider higher dimensional topological Taub-NUT/Bolt-AdS solutions where a cosmological constant is treated as a pressure. The thermodynamic quantities of these solutions are explicitly calculated. Furthermore, we find these thermodynamic quantities satisfy the Clapeyron equation. In particular, a new thermodynamically stable region for the NUT solution is found by studying the Gibbs free energy. Intriguingly, we also find that like the AdS black hole case, the G-T diagram of the Bolt solution has two branches which are joined at a minimum temperature. The Bolt solution with the large radius, at the lower branch, becomes stable beyond a certain temperature while the Bolt solution with the small radius, at the upper branch, is always unstable.Comment: 7 pages, 6 figures, typos corrected, version to appear in PL

The Extended Thermodynamic Properties of Taub-NUT/Bolt-AdS spaces

We investigate the extended thermodynamic properties of higher-dimensional Taub-NUT/Bolt-AdS spaces where a cosmological constant is treated as a pressure. We find a general form for thermodynamic volumes of Taub-NUT/Bolt-AdS black holes for arbitrary dimensions. Interestingly, it is found that the Taub-NUT-AdS metric has a thermodynamically stable range when the total number of dimensions is a multiple of 4 (4, 8, 12, ...). We also explore their phase structure and find the first order phase transition holds for higher-dimensional cases.Comment: 18 pages, 5 figures, typos corrected, references added, version to appear in PL

Late Time Behaviors of an Inhomogeneous Rolling Tachyon

We study an inhomogeneous decay of an unstable D-brane in the context of Dirac-Born-Infeld~(DBI)-type effective action. We consider tachyon and electromagnetic fields with dependence of time and one spatial coordinate, and an exact solution is found under an exponentially decreasing tachyon potential, $e^{-|T|/\sqrt{2}}$, which is valid for the description of the late time behavior of an unstable D-brane. Though the obtained solution contains both time and spatial dependence, the corresponding momentum density vanishes over the entire spacetime region. The solution is governed by two parameters. One adjusts the distribution of energy density in the inhomogeneous direction, and the other interpolates between the homogeneous rolling tachyon and static configuration. As time evolves, the energy of the unstable D-brane is converted into the electric flux and tachyon matter.Comment: 17 pages, 1 figure, version to appear in PR

Configurational entropy of tachyon kinks on unstable Dp-branes

We consider tachyon effective theory with Born-Infeld electromagnetic fields and investigate the configurational entropy of the various tachyon kink solutions. We find that the configurational entropy stats at a minimum value and saturates to a maximum value as the negative pressure of pure tachyonic field increases. In particular, when an electric field is turned on and its magnitude is larger than or equal to the critical value, we find the configurational entropy has a global minimum, which is related to the predominant tachyonic states.Comment: 9 pages, 20 figures, typos corrected, added comments and references, version to appear in PL

Quasi-Normal Modes of a Natural AdS Wormhole in Einstein-Born-Infeld Gravity

We study the matter perturbations of a new AdS wormhole in (3+1)-dimensional Einstein-Born-Infeld gravity, called "natural wormhole", which does not require exotic matters. We discuss the stability of the perturbations by numerically computing the quasi-normal modes (QNMs) of a massive scalar field in the wormhole background. We investigate the dependence of quasi-normal frequencies on the mass of scalar field as well as other parameters of the wormhole. It is found that the perturbations are always stable for the wormhole geometry which has the general relativity (GR) limit when the scalar field mass m satisfies a certain, tachyonic mass bound m^2 > m^2_* with m^2_* < 0, analogous to the Breitenlohner-Freedman (BF) bound in the global-AdS space, m^2_BF = 3 Lambda/4. It is also found that the BF-like bound m^2_* shifts by the changes of the cosmological constant Lambda or angular-momentum number l, with a level crossing between the lowest complex and pure-imaginary modes for zero angular momentum l = 0. Furthermore, it is found that the unstable modes can also have oscillatory parts as well as non-oscillatory parts depending on whether the real and imaginary parts of frequencies are dependent on each other or not, contrary to arguments in the literature. For wormhole geometries which do not have the GR limit, the BF-like bound does not occur and the perturbations are stable for arbitrary tachyonic and non-tachyonic masses, up to a critical mass m^2_c > 0 where the perturbations are completely frozen.Comment: Added comments and references, Accepted in EPJ