Asad Naqvi

Open strings from N = 4 super Yang-Mills

Exploiting insights on strings moving in pp-wave backgrounds, we show how open strings emerge from N = 4 SU(M) Yang-Mills theory as fluctuations around certain states carrying R-charge of order M. These states are dual to spherical D3-branes of AdS_5 x S^5 and we reproduce the spectrum of small fluctuations of these states from Yang Mills theory. When G such D3-branes coincide, the expected G^2 light degrees of freedom emerge. The open strings running between the branes can be quantized easily in a Penrose limit of the spacetime. Taking the corresponding large charge limit of the Yang-Mills theory, we reproduce the open string worldsheets and their spectra from field theory degrees of freedom.

On marginal deformations in superstring field theory

We use level truncated superstring field theory to obtain the effective potential for the Wilson line marginal deformation parameter which corresponds to the constant vacuum expectation value of the U(1) gauge field on the D-brane in a particular direction. We present results for both the BPS and the non-BPS D-brane. In the case of non-BPS D-brane the effective potential has branches corresponding to the extrema of the tachyon potential. In the branch with vanishing tachyon vev (M-branch), the effective potential becomes flatter as the level of the approximation is increased. The branch which corresponds to the stable vacuum after the tachyon has condensed (V-branch) exists only for a finite range of values of marginal deformation parameter. We use our results to find the mass of the gauge field in the stable tachyonic vacuum. We find this mass to be of a non-zero value which seems to stabilize as the level approximation is improved.

Coulomb branch of N=2 supersymmetric product group theories from branes

We determine the low-energy description of N=2 supersymmetric {Pi}{sub i} SU(k{sub i}) gauge theories with bifundamental and fundamental matter based on M-theory five-brane configurations. The dependence on moduli and scales of the coefficients in the nonhyperelliptic Seiberg-Witten curves for these theories are determined by considering various field theory and brane limits. A peculiarity in the interpretation of these curves for the vanishing {beta}-function case is noted. {copyright} {ital 1998} {ital The American Physical Society}

Marginal deformations from branes

We study brane configurations for four dimensional = 1 supersymmetric gauge theories with quartic superpotentials which flow in the infrared to manifolds of interacting superconformal fixed points. We enumerate finite = 2 theories, from which a large class of marginal = 1 theories descend. We give the brane descriptions of these theories in Type IIA and Type IIB string theory. The Type IIB descriptions are in terms of D3 branes in orientifold and generalized conifold backgrounds. We calculate the Weyl and Euler anomalies in these theories, and find that they are equal in elliptic models and unequal in a large class of finite = 2 and marginal = 1 non-elliptic theories.

Propagators for massive symmetric tensor and p-forms in AdSd+1

We construct propagators in euclidean AdSd+1 space-time for massive p-forms and massive symmetric tensors.

Towards a topological G(2) string

We define new topological theories related to sigma models whose tar- get space is a 7 dimensional manifold of G2 holonomy. We show how to define the topological twist and identify the BRST operator and the physical states. Correlation functions at genus zero are computed and related to Hitchins topological action for three-forms. We con- jecture that one can extend this definition to all genus and construct a seven-dimensional topological string theory. In contrast to the four- dimensional case, it does not seem to compute terms in the low-energy effective action in three dimensions.