A Note on the Hitchin System in a Background B-field

The space of solutions to the Hitchin equations on the dual torus with punctures determines the Higgs branch of certain impurity theories. An alternative description of this Higgs branch is provided, in terms of the proper deformation of Hitchin system with deformation parameter given by a $B$-field. For the dual torus minus the singular points we construct explicit solutions to the B-deformed Hitchin equations by reducing them to principal chiral model equations and then using deformation quantization methods.Comment: 10 pages, harvmac file, no figures, added reference

N=2 String Geometry and the Heavenly Equations

In this paper we survey some of the relations between Plebanski description of self-dual gravity through the heavenly equations and the physics (and mathematics) of N=2 Strings. In particular we focus on the correspondence between the infinite hierarchy in the ground ring structure of BRST operators and its associated Boyer-Plebanski construction of infinite conserved quantities in self-dual gravity. We comment on ``Mirror Symmetry'' in these models and the large-N duality between topological N=4 gauge theories in two dimensions and topological gravity in four dimensions. Finally D-branes in this context are briefly outlined.Comment: 19+1 pages, 3 figures, corrected types, added references and comments,to appear in the proceedings of the conference: Topics in Mathematical Physics, General Relativity, and Cosmology, On the Occasion of the 75th Birthday of Jerzy F. Plebanski (2002). September 17-20, 2002; Cinvestav, Mexico Cit

Self-dual gravity via Hitchin's equations

In this work half-flat metrics are obtained from Hitchin's equations. The SU$(\infty)$ Hitchin's equations are obtained and as a consequence of them, the Husain-Park equation is found. Considering that the gauge group is SU$(2)$, some solutions associated to Liouville, sinh-Gordon and Painlev\'e III equations are taken and, through Moyal deformations, solutions of the SU$(\infty)$ Hitchin's equations are obtained. From these solutions, hamiltonian vector fields are determined, which in turn are used to construct the half-flat metrics. Following an approach of Dunajski, Mason and Woodhouse, it is also possible to construct half-flat metrics on ${\cal M} \times\mathbb{CP}^{1}$.Comment: 27+1 pages, no figure

Gauged WZW Models Via Equivariant Cohomology

The problem of computing systematically the gauge invariant extension of WZW term through equivariant cohomology is addressed. The analysis done by Witten in the two-dimensional case is extended to the four-dimensional ones. While Cartan's model is used to find the anomaly cancelation condition. It is shown that the Weil model is more appropriated to find the gauge invariant extension of the WZW term. In the process we point out that Weil's and Cartan's models are also useful to stress some connections with the abelian anomaly.Comment: 10 pages, no figure

Remarks on Noncommutative Solitons

In the first part of this work we consider an unstable non-BPS Dp-\bar{Dp}-brane pair in Type II superstring theory. Turning on a background NS-NS B-field (constant and nonzero along two spatial directions), we show that the tachyon responsible for the unstability has a complex GMS solitonic solution, which is interpreted as the low energy remnant of the resulting D(p-2)-brane. In the second part, we apply these results to construct the noncommutative soliton analogous of Witten's superconducting string. This is done by considering the complex GMS soliton arising from the D3-\bar{D3}-brane annihilation in Type IIB superstring theory. In the presence of left-handed fermions, we apply the Weyl-Wigner-Moyal correspondence and the bosonization technique to show that this object behaves like a superconducting wire.Comment: 24+1 pages, harvmac file, no figures, corrected typos, major clarification

Lectures on Strings, D-branes and Gauge Theories

In these lectures we review the basic ideas of perturbative and non-perturbative string theory. On the non-perturbative side we give an introduction to D-branes and string duality. The elementary concepts of non-BPS branes and noncommutative gauge theories are also discussed.Comment: 37+1 pages, LaTeX file, no figure

On the Berezin Description of Kahler Quotients

We survey geometric quantization of finite dimensional affine Kahler manifolds. Its corresponding prequantization and the Berezin's deformation quantization formulation, as proposed by Cahen et al., is used to quantize their corresponding Kahler quotients. Equivariant formalism greatly facilitates the description.Comment: 10 pages, latex file, no figures, minor clarifications and misprints corrected, contribution to the Proceedings of the First Mexican Meeting on Mathematical and Experimental Physics, Mexico Cit

A Reduced Model of Noncommutative S-brane Spectrum

CFT construction of S-branes describing the rolling and bouncing tachyons is analyzed in the context of a $\theta$-noncommutative deformation of minisuperspace. Half s-brane and s-brane in the noncommutative minisuperspace are analyzed and exact analytic solutions, involving the noncommutative parameter $\theta$ and compatible with the boundary conditions at infinity, are found. Comparison with the usual commutative minisuperspace is finally performed.Comment: 19 pages, latex, 2 eps figures; v2/v3 references adde

A q-deformed Version of the Heavenly Equations

Using a $q$-deformed Moyal algebra associated with the group of area preserving diffeomorphisms of th two-dimensional torus $T^2$, sdiff$_q (T^2)$, a $q$-deformed version for the Heavenly equations is given. Finally, the two-dimensional chiral version of Self-dual gravity in this $q$-deformed context is briefly discussed.Comment: 18 pages. LaTex, no figures, extended and corrected versio

Radiation Damping of a Yang-Mills Particle Revisited

The problem of a color-charged point particle interacting with a four dimensional Yang-Mills gauge theory is revisited. The radiation damping is obtained inspired in the Dirac's computation. The difficulties in the non-abelian case were solved by using an ansatz for the Li\'enard-Wiechert potentials, already used in the literature for finding solutions to the Yang-Mills equations. Three non-trivial examples of radiation damping for the non-abelian particle are discussed in detail.Comment: 33 pages, no figures, typos corrected, references adde