Thermodynamic Curvature of the BTZ Black Hole

Some thermodynamic properties of the Ba\~nados-Teitelboim-Zanelli (BTZ) black hole are studied to get the effective dimension of its corresponding statistical model. For this purpose, we make use of the geometrical approach to the thermodynamics: Considering the black hole as a thermodynamic system with two thermodynamic variables (the mass $M$ and the angular momemtum $J$), we obtain two-dimensional Riemannian thermodynamic geometry described by positive definite Ruppeiner metric. From the thermodynamic curvature we find that the extremal limit is the critical point. The effective spatial dimension of the statistical system corresponding to the near-extremal BTZ black holes is one. Far from the extremal point, the effective dimension becomes less than one, which leads to one possible speculation on the underlying structure for the corresponding statistical model.Comment: 19 pages, LaTeX with revtex macro, 4 figures in eps file

Holography: 2-D or not 2-D?

As was recently pointed out by Cadoni, a certain class of two-dimensional gravitational theories will exhibit (black hole) thermodynamic behavior that is reminiscent of a free field theory. In the current letter, a direct correspondence is established between these two-dimensional models and the strongly curved regime of (arbitrary-dimensional) anti-de Sitter gravity. On this basis, we go on to speculatively argue that two-dimensional gravity may ultimatley be utilized for identifying and perhaps even understanding holographic dualities.Comment: 8 pages, Revtex; (v2) references and footnote added; (v3) discussion on page 5 revise

Entropic force and its cosmological implications

We investigate a possibility of realizing the entropic force into the cosmology. A main issue is how the holographic screen is implemented in the Newtonian cosmology. Contrary to the relativistic realization of Friedmann equations, we do not clarify the connection between Newtonian cosmology and entropic force because there is no way of implementing the holographic screen in the Newtonian cosmology.Comment: 16 pages, no figures, version "Accepted for publication in Astrophysics & Space Science

Black holes in the Einstein -Gauss-Bonnet theory and the geometry of their thermodynamics-II

In the present work we study (i) charged black hole in Einstein-Gauss-Bonnet (EGB) theory, known as Einstein-Maxwell-Gauss-Bonnet (EMGB) black hole and (ii) black hole in EGB gravity with Yang-Mills field. The thermodynamic geometry of these two black hole solutions has been investigated, using the modified entropy in Gauss-Bonnet theory.Comment: 7 page

Brane Cosmology in the Background of D-Brane with NS B Field

We study the cosmological evolution of the four-dimensional universe on the probe D3-brane in geodesic motion in the curved background of the source Dp-brane with non-zero NS B field. The Friedman equations describing the expansion of the brane universe are obtained and analyzed for various limits. We elaborate on corrections to the cosmological evolution due to nonzero NS B field.Comment: 13 pages, LaTeX, revised version with minor corrections to appear in Phys. Rev.

Parity and Time Reversal in the Spin-Rotation Interaction

A recently reported discrepancy between experimental and theoretical values of the muon's g-2 factor is interpreted as due to small violations of the conservation of P and T in the spin-rotation coupling. The experiments place an upper limit on these violations and on the weight change of spinning gyroscopes.Comment: 3 page

The Gregory-Laflamme instability for the D2-D0 bound state

The D2-D0 bound state exhibits a Gregory-Laflamme instability when it is sufficiently non-extremal. If there are no D0-branes, the requisite non-extremality is finite. When most of the extremal mass comes from D0-branes, the requisite non-extremality is very small. The location of the threshhold for the instability is determined using a local thermodynamic analysis which is then checked against a numerical analysis of the linearized equations of motion. The thermodynamic analysis reveals an instability of non-commutative field theory at finite temperature, which may occur only at very long wavelengths as the decoupling limit is approached.Comment: 19 pages, Latex2e. v2: two refs added. v3: clearer exposition in section

Hawking-Page Phase Transition of black Dp-branes and R-charged black holes with an IR Cutoff

We show that the confinement-deconfinement phase transition of supersymmetric Yang-Mills theories with 16 supercharges in various dimensions can be realized through the Hawking-Page phase transition between the near horizon geometries of black Dp-branes and BPS Dp-branes by removing a small radius region in the geometry in order to realize a confinement phase, which generalizes the Herzog's discussion for the holographic hard-wall AdS/QCD model. Removing a small radius region in the gravitational dual corresponds to introducing an IR cutoff in the dual field theory. We also discuss the Hawking-Page phase transition between thermal $AdS_5$, $AdS_4$, $AdS_7$ spaces and R-charged AdS black holes coming from the spherical reduction of the decoupling limit of rotating D3-, M2-, and M5- branes in type IIB supergravity and 11 dimensional supergravity in grand canonical ensembles, where the IR cutoff also plays a crucial role in the existence of the phase transition.Comment: 34 pages, 18 figures, JHEP3, v2, references added, v3, some explanations adde

Light-like noncommutativity and duality from open strings/branes

In this paper we perform some non-trivial tests for the recently obtained open membrane/D-brane metrics and `generalized' noncommutativity parameters using Dp/NS5/M5-branes which have been deformed by light-like fields. The results obtained give further evidence that these open membrane/D-brane metrics and `generalized' noncommutativity parameters are correct. Further, we use the open brane data and supergravity duals to obtain more information about non-gravitational theories with light-like noncommutativity, or `generalized' light-like noncommutativity. In particular, we investigate various duality relations (strong coupling limits). In the light-like case we also comment on the relation between open membrane data (open membrane metric etc.) in six dimensions and open string data in five dimensions. Finally, we investigate the strong coupling limit (high energy limit) of five dimensional NCYM with \Theta^{12}=\Theta^{34}. In particular, we find that this NCYM theory can be UV completed by a DLCQ compactification of M-theory.Comment: 24 pages, Latex. v2:Comments and references added. v3:Version published in JHE

Scalar-Tensor Theory of Gravity and Generalized Second Law of Thermodynamics on the Event Horizon

In blackhole physics, the second law of thermodynamics is generally valid whether the blackhole is a static or a non-static one. Considering the universe as a thermodynamical system the second law of blackhole dynamics extends to the non-negativity of the sum of the entropy of the matter and the horizon, known as generalized second law of thermodynamics(GSLT). Here, we have assumed the universe to be bounded by the event-horizon or filled with perfect fluid and holographic dark energy in two cases. Thus considering entropy to be an arbitrary function of the area of the event-horizon, we have tried to find the conditions and the restrictions over the scalar field and equation of state for the validity of the GSLT and both in quintessence-era and in phantom-era in scalar tensor theory.Comment: 8 page