Statistical entropy of near-extremal and fundamental black p-branes

The problem of asymptotic density of quantum states of fundamental extended objects is revised in detail. We argue that in the near-extremal regime the fundamental $p$-brane approach can yield a microscopic interpretation of the black hole entropy. The asymptotic behavior of partition functions, associated with the $p$-branes, and the near-extremal entropy of five-dimensional black holes are explicitly calculated.Comment: 15 pages, LateX file.Minor changes,refs added, version to appear in Progr.Theor.Phy

Aharonov-Bohm effect in circular carbon nanotubes

We study the interference of interacting electrons in toroidal single-wall carbon nanotubes coupled to metallic electrodes by tunnel junctions. The dc conductance shows resonant features as a function of the gate voltage and the magnetic field. The conductance pattern is determined by the interaction parameter, which in turn can be cross-checked against the exponents governing the transport at high temperatures. The coordinate dependence of the conductance reflects electron correlations in one-dimensional space.Comment: 2 pages, contributed paper to LT-22, style file phbauth.cls is include

Running surface couplings

We discuss the renormalization group improved effective action and running surface couplings in curved spacetime with boundary. Using scalar self-interacting theory as an example, we study the influence of the boundary effects to effective equations of motion in spherical cap and the relevance of surface running couplings to quantum cosmology and symmetry breaking phenomenon. Running surface couplings in the asymptotically free SU(2) gauge theory are found.Comment: 11 pages, Latex fil

The Renormalization Group and the Effective Potential in a Curved Spacetime with Torsion

The renormalization group method is employed to study the effective potential in curved spacetime with torsion. The renormalization-group improved effective potential corresponding to a massless gauge theory in such a spacetime is found and in this way a generalization of Coleman-Weinberg's approach corresponding to flat space is obtained. A method which works with the renormalization group equation for two-loop effective potential calculations in torsionful spacetime is developed. The effective potential for the conformal factor in the conformal dynamics of quantum gravity with torsion is thereby calculated explicitly. Finally, torsion-induced phase transitions are discussed.Comment: 16 pages, LaTeX file, figures available from the author

HIGH TEMPERATURE EXPANSION OF STRING FREE ENERGY IN HYPERBOLIC SPACE

The high temperature behaviour of the open bosonic string free energy in the space $S^1 \otimes H^N$ with vanishingly small curvature is investigated. The leading term of the high temperature expansion of the one-loop free energy, near the Hagedorn instability, is obtained. The problem of infrared regularization of thermodynamical quantities is pointed out. For minimally coupling quantum fields related to the normal modes of strings, the results are similar to the ones valid for Rindler space. In the lower mass string states regime a connection with the quantum corrections to the black hole entropy is outlined.Comment: 7 pages, latex file, no figures

Fermionic Casimir densities in anti-de Sitter spacetime

The fermionic condensate and vacuum expectation value of the energy-momentum tensor, for a massive fermionic field on the background of anti-de Sitter spacetime, in the geometry of two parallel boundaries with bag boundary conditions, are investigated. Vacuum expectation values, expressed as series involving the eigenvalues of the radial quantum number, are neatly decomposed into boundary-free, single-boundary-induced, and second-boundary-induced parts, with the help of the generalized Abel-Plana summation formula. In this way, the renormalization procedure is very conveniently reduced to the one corresponding to boundary-free AdS spacetime. The boundary-induced contributions to the fermionic condensate and to the vacuum expectation value of the energy density are proven to be everywhere negative. The vacuum expectation values are exponentially suppressed at distances from the boundaries much larger than the curvature radius of the AdS space. Near the boundaries, effects related with the curvature of the background spacetime are shown to be subdominant and, to leading order, all known results for boundaries in the Minkowski bulk are recovered. Zeta function techniques are successfully used for the evaluation of the total vacuum energy in the region between the boundaries. It is proven that the resulting interaction forces between them are attractive and that, for large separations, they also decay exponentially. Finally, our results are extended and explicitly translated to fermionic Casimir densities in braneworld scenarios of Randall-Sundrum type.Comment: 22 pages, 2 figure