Black hole dynamics from instanton strings

A D-5-brane bound state with a self-dual field strength on a 4-torus is considered. In a particular case this model reproduces the D5-D1 brane bound state usually used in the string theory description of 5-dimensional black holes. In the limit where the brane dynamics decouples from the bulk the Higgs and Coulomb branches of the theory on the brane decouple. Contrasting with the usual instanton moduli space approximation to the problem the Higgs branch describes fundamental excitations of the gauge field on the brane. Upon reduction to 2-dimensions it is associated with the so-called instanton strings. Using the Born-Infeld action for the D-5-brane we determine the coupling of these strings to a minimally coupled scalar in the black hole background. The supergravity calculation of the cross section is found to agree with the D-brane absorption probability rate calculation. We consider the near horizon geometry of our black hole and elaborate on the corresponding duality with the Higgs branch of the gauge theory in the large N limit. A heuristic argument for the scaling of the effective string tension is given.Comment: 37 pages, latex. Typos corrected, SUSY field configuration argued to be valid even when DBI corrections are important and two references adde

Black Composite M-branes

We generalise all the known supersymmetric composite M-branes to the corresponding black configurations. Thermodynamical formulae is written by using the simple rules to construct these black branes.Comment: 14 pages, latex. Revised version to appear in Nuclear Physics

Conformal correlators of mixed-symmetry tensors

We generalize the embedding formalism for conformal field theories to the case of general operators with mixed symmetry. The index-free notation encoding symmetric tensors as polynomials in an auxiliary polarization vector is extended to mixed-symmetry tensors by introducing a new commuting or anticommuting polarization vector for each row or column in the Young diagram that describes the index symmetries of the tensor. We determine the tensor structures that are allowed in n-point conformal correlation functions and give an algorithm for counting them in terms of tensor product coefficients. A simple derivation of the unitarity bound for arbitrary mixed-symmetry tensors is obtained by considering the conservation condition in embedding space. We show, with an example, how the new formalism can be used to compute conformal blocks of arbitrary external fields for the exchange of any conformal primary and its descendants. The matching between the number of tensor structures in conformal field theory correlators of operators in d dimensions and massive scattering amplitudes in d+1 dimensions is also seen to carry over to mixed-symmetry tensors.Comment: 46 pages, many figures, v2: Reformulated the counting of tensor structures, new section on conserved operators, v3: fixed typo

Landau degeneracy and black hole entropy

We consider the supergravity solution describing a configuration of intersecting D-4-branes with non-vanishing worldvolume gauge fields. The entropy of such a black hole is calculated in terms of the D-branes quantised charges. The non-extreme solution is also considered and the corresponding thermodynamical quantities are calculated in terms of a D-brane/anti-D-brane system. To perform the quantum mechanical D-brane analysis we study open-strings with their ends on branes with a magnetic condensate. Applying the results to our D-brane system we managed to have a perfect agreement between the D-brane entropy counting and the corresponding semi-classical result. The Landau degeneracy of the open string states describing the excitations of the D-brane system enters in a crucial way. We also derive the near-extreme results which agree with the semi-classical calculations.Comment: 30 pages, 1 figure, latex. Minor corrections, version to appear in Nuclear Physics