Arvind Rajaraman

Tachyon condensation in noncommutative gauge theory

Abstract We show that the decay of the D 2 – D 2 system with large worldvolume magnetic fields can be described in noncommutative gauge theory. Tachyon condensation in this system describes the annihilation of D 2 – D 2 into D 0 -branes. From the (2+1) -dimensional point of view, this is the decay of a nonabelian magnetic flux into vortices. The semiclassical approximation is valid over a long period of the decay. Our analysis allows us to clarify earlier results in the literature related to tachyon condensation and noncommutative gauge theory.

Green-Schwarz string action on AdS 3 × S 3 with Ramond-Ramond charge

We derive the classical kappa-symmetric Type IIB string action on AdS(3) x S(3) by employing the SU(1,1|2)^2 algebra. We then gauge fix kappa-symmetry in the background adapted Killing spinor gauge and present the action in a very simple form.

Noncommutative gauge theory, divergences and closed strings

We study the renormalization of non-commutative gauge theories with matter. As in the scalar field theory cases, there are logarithmic infrared divergences resulting from integrating out high momentum modes. In order to reproduce the correct infrared behaviour, the wilsonian effective action has to include certain ``closed string modes with prescribed couplings. In the case of quiver gauge theories, realized in string theory on orbifolds, we identify the required modes with a set of twisted sector fields. These closed string modes have exactly the prescribed couplings to correct the wilsonian effective action. This provides a concrete origin for the appearance of closed string modes in noncommutative field theories.

Boundary states for D-branes in AdS 3 space

We construct boundary states representing D-strings in

Orientifold points in M theory

AdS_3

D-branes on asymmetric orbifolds

. These wrap twisted conjugacy classes of SL(2,R), and the boundary states are therefore based on continuous representations only. We check Cardys condition and find a consistent open string spectrum. The open string spectrum on all the D-branes is the same.

On the quantization of the GS string on AdS5×S5

We identify the lift to M theory of the four types of orientifold points, and show that they involve a chiral fermion on an orbifold fixed circle. From this lift, we compute the number of normalizable ground states for the SO(N) and Sp(N) supersymmetric quantum mechanics with sixteen supercharges. The results agree with known results obtained by the mass deformation method. The mass of the orientifold is identified with the Casimir energy.

Supergravity solutions for localised brane intersections

Abstract We construct D-brane states on an asymmetric orbifold of type IIA on a four-torus, which is modded out by T -duality. We find explicit boundary states charged under the twisted sector gauge fields. Unlike other cases, the boundary states involve an explicit dependence on the twist fields. The D-brane spectrum is consistent with the model being equivalent to type IIA on a four-torus.

Supergravity Duals for N = 2 Gauge Theories

Abstract We discuss the quantization of the Green-Schwarz string action on AdS5×S5. We construct consistent, globally well-defined, gauge fixing choices for kappa symmetry and worldsheet diffeomorphism invariance. We then proceed to quantize the theory in a perturbation series in the inverse radius of curvature, in a background field expansion. We discuss vertex operators and correlation functions.

D-branes in linear dilaton backgrounds

We present a general method for constructing supergravity solutions for intersecting branes. The solutions are written in terms of a single function, which is the solution to a nonlinear differential equation. We illustrate this procedure in detail for the case of M2-branes ending on M5-branes. We also present supergravity solutions for strings ending on Dp-branes. Unlike previous results in the literature, these branes are completely localized.