Tunneling between de Sitter and anti de Sitter black holes in a noncommutative D3-brane formalism

We obtain dS and AdS generalized Reissner-Nordstrom like black hole geometries in a curved D3-brane frame-work, underlying a noncommutative gauge theory on the brane-world. The noncommutative scaling limit is explored to investigate a possible tunneling of an AdS vacuum in string theory to dS vacuum in its low energy gravity theory. The Hagedorn transition is invoked into its self-dual gauge theory to decouple the gauge nonlinearity from the dS geometry, which in turn is shown to describe a pure dS vacuum.Comment: 7-page

Generalized Dirichlet Branes and Zero-modes

We investigate the effective dynamics of an arbitrary Dirichlet p-brane, in a path-integral formalism, by incorporating the massless excitations of closed string modes in open bosonic string theory. It is shown that the closed string background fields in the bosonic sector of type II theories induce invariant extrinsic curvature on the world-volume. In addition, the curvature can be seen to be associated with a divergence at the boundary of string world-sheet. The re-normalization of the collective coordinates, next to leading order in its derivative expansion, is performed to handle the divergence and the effective dynamics is encoded in Dirac-Born-Infeld action. Furthermore, the collective dynamics is generalized to include appropriate fermionic partners in type I super-string theory. The role of string modes is reviewed in terms of the collective coordinates and the gauge theory on the world-volume is argued to be non-local in presence of the U(1) invariant field strength.Comment: LaTex, 20 pages, v2: minor changes and added references v3:typos corrected, some statements are clarified in the context of zero-mode

Hidden Isometry in a Chiral Gauged WZW Model

It is shown that the asymmetric chiral gauging of the WZW models give rise to consistent string backgrounds. The target space structure of the ${[{SL(2,\Re)/ {SO(1,1)}}]}_L \bigotimes {[{SL(2,\Re)/U(1)}]}_R$ model is analyzed and the presence of a hidden isometry in this background is demonstrated. A nonlinear coordinate transformation is obtained which transforms the asymmetric model to the symmetric one, analyzed recently by two of the present authors.Comment: 11 pages, IP/BBSR/92-67, IISC/CTS/92-

Quintessence and effective AdS brane geometries

A geometric torsion dynamics leading to an effective curvature in a second order formalism on a D4-brane is revisited with a renewed interest. We obtain two effective $AdS_4$ brane geometries on a vacuum created pair of $(D{\bar D})_3$-brane. One of them is shown to describe an AdS Schwarzschild spinning black hole and the other is shown to describe a spinning black hole bound state. It is argued that a D-instanton in a vacuum created anti D3-brane within a pair may describe a quintessence. It may seen to incorporate a varying vacuum energy density in a brane universe. We consider the effective curvature scalar on $S^1\times S^1$ to analyze torsion-less geometries on a vacuum created pair of $(D{\bar D})_2$-brane. The emergent $AdS_3$ brane is shown to describe a Schwarzschild and a Reissner-Nordstrom (RN) geometries in presence of extra dimension(s).Comment: 20 pages, expanded discussion and added referenc