Comments on Higher Derivative Terms for the Tachyon Action

We consider the open string tachyon action in a world-sheet sigma model approach. We present explicit calculations up to order 8 in derivatives for the bosonic string, and mimic these to order 6 for the superstring, including terms with multiple derivatives acting on the tachyon field. We reproduce lower derivative terms obtained elsewhere, and speculate on the role of the world-sheet contact terms regularizing the action for the superstring tachyon.Comment: 21 page

Chiral Symmetry Breaking in Brane Models

We discuss the chiral symmetry breaking in general intersecting Dq/Dp brane models consisting of N_c Dq-branes and a single Dp-brane with an s-dimensional intersection. There exists a QCD-like theory localized at the intersection and the Dq/Dp model gives a holographic description of it. The rotational symmetry of directions transverse to both of the Dq and Dp-branes can be identified with a chiral symmetry, which is non-Abelian for certain cases. The asymptotic distance between the Dq-branes and the Dp-brane corresponds to a quark mass. By studying the probe Dp-brane dynamics in a Dq-brane background in the near horizon and large N_c limit we find that the chiral symmetry is spontaneously broken and there appear (pseudo-)Nambu-Goldstone bosons. We also discuss the models at finite temperature.Comment: 29pages, 14figures. v2: a reference added. v3: 27pages, 12figures, two references added, discussions on s=q configurations are corrected. v4: minor change in Sec.

The String Dual of an N=(4,0){\cal N}=(4,0) Two-Dimensional Gauge Theory

We find solutions of the six-dimensional maximal supergravity by adding a perturbation of vector fields to the solution AdS${}_3$ $\times$ S${}^3$. For certain perturbations the solution represents a dual description of an ${\cal N}=(4,0)$ field theory in two dimensions by the AdS/CFT correspondence.Comment: 8 pages, no figur

A Note on Supersymmetry in Noncommutative Field Theories

We show that a solution of the type IIB supergravity representing D3-branes in the presence of a 2-form background has 16 supersymmetries by explicitly constructing the transformation parameter of unbroken supersymmetry. This solution is dual to a noncommutative Yang-Mills theory in a certain limit.Comment: 10 pages, no figure

Super Weyl Anomalies in the AdS/CFT Correspondence

Anomalies of N = (4,4) superconformal field theories coupled to a conformal supergravity background in two dimensions are computed by using the AdS/CFT correspondence. We find that Weyl, axial gauge and super Weyl transformations are anomalous, while general coordinate, local Lorentz, vector gauge and local super transformations are not. The coefficients of the anomalies show that the superconformal field theories have the central charge expected in the AdS/CFT correspondence.Comment: 16 pages, LaTeX, references added and typos correcte

Supersymmetry in the AdS/CFT Correspondence

We study how local symmetry transformations of (p, q) anti de Sitter supergravities in three dimensions act on fields on the two-dimensional boundary. The boundary transformation laws are shown to be the same as those of two-dimensional (p, q) conformal supergravities for p, q \leq 2. Weyl and super Weyl transformations are generated from three-dimensional general coordinate and super transformations.Comment: 11 pages, LaTe

Perturbations and Supersymmetries in AdS_3/CFT_2

Symmetry breaking by perturbations in the AdS/CFT correspondence is discussed. Perturbations of vector fields to the AdS_3 x S^3 solution of the six-dimensional N=(4,4) supergravity are considered. These perturbations are identified as descendents of chiral primary operators of a two-dimensional N=(4,4) CFT with conformal weight (2,2) or (1,1). We examine unbroken symmetries by the perturbations in the CFT side as well as in the supergravity side and find the same result: the N=(4,2) or N=(2,4) Poincare supersymmetry for the (2,2) perturbation and the N=(0,4) or N=(4,0) superconformal symmetry for the (1,1) perturbation.Comment: 23 pages, LaTeX, Minor change