Modern Physics Letters A

For the D-branes on the SL(2,R) WZW model we present a particular choice of outer automorphism for the gluing condition of currents that leads to a special AdS₂ brane configuration. This configuration is shown to be a static solution in the cylindrical coordinates, and a nonstatic solution in the Poincaré coordinates to the nonlinear equation of motion for the Dirac–Born–Infeld action of a D-string. The generalization of it gives a family of nonstatic AdS₂ brane solutions. They are demonstrated to transform to each other under the isometry group of AdS₃ space–time.

We analyze the relation between the Lagrangian and Hamiltonian BRST symmetry generators for a recently proposed two-dimensional symmetry. In particular it is shown that this symmetry may be obtained from a canonical transformation in the ghost sector in a gauge-independent way.

The n-instanton contribution to the Seiberg–Witten prepotential of N = 2 supersymmetric d = 4 Yang–Mills theory is represented as the integral of the exponential of an equivariantly exact form. Integrating out an overall scale and a U(1) angle the integral is rewritten as (4n - 3)-fold product of a closed two-form. This two-form is, formally, a representative of the Euler class of the instanton moduli space viewed as a principal U(1) bundle, because its pullback under bundle projection is the exterior derivative of an angular one-form.

By using the so-called Information Metric on the moduli space of an anti-self-dual (ASD) Instanton in a self-dual (SD) noncommutative background, we investigate the geometry of moduli space. The metric is evaluated perturbatively in noncommutativity parameter and we show that by putting a cutoff in the location of instanton in the definition of Information Metric we can recover the five-dimensional space–time in the presence of a B-field. This result shows that the noncommutative YM-Instanton Moduli corresponds to D-Instanton Moduli in the gravity side where the radial and transverse location of D-Instanton correspond to YM-Instanton size and location, respectively. The match is shown in the first order of noncommutativity parameter.

We study string-loop corrections to magnetic black hole. Four-dimensional theory is obtained by compactification of the heterotic string theory on the manifold K3×T² or on a suitable orbifold yielding N=1 supersymmetry in 6D. The resulting 4D theory has N=2 local supersymmetry. Prepotential of this theory receives only one-string-loop correction. The tree-level gauge couplings are proportional to the inverse effective string coupling and decrease at small distances from the center of magnetic black hole, so that loop corrections to the gauge couplings are important in this region. We solve the system of Killing spinor equations (conditions for the supersymmetry variations of the fermions to vanish) and Maxwell equations. At the string-tree level, we reproduce the magnetic black hole solution which can also be obtained by solving the system of the Einstein–Maxwell equations and the equations of motion for the moduli. String-loop corrections to the tree-level solution are calculated in the first order in string coupling. The resulting corrections to the metric and dilaton are large at small distances from the center of the black hole. Possible smearing of the singularity at the origin by quantum corrections is discussed.