Non-Critical Strings in Robertson-Walker Space Time

I consider a D+1 dimensional nonlinear $\sigma$ model based on a possible interpretation of the Liouville field as a physical time. The Weyl invariance of this theory gives us restrictions for the background fields and the parameters of the theory, e.g.\ for trivial background one obtains the known regions for the dimension of the space-time ($\leq$1 or $\geq$25). For a Robertson-Walker space time a special solution of these equations is discussed.Comment: 9 page

Quantum Corrections for a Cosmological String Solution

We investigate quantum corrections for a cosmological solution of the string effective action. Starting point is a classical solution containing an antisymmetric tensor field, a dilaton and a modulus field which has singularities in the scalar fields. As a first step we quantize the scalar fields near the singularity with the result that the singularities disappear and that in general non-perturbative quantum corrections form a potential in the scalar fields.Comment: talk presented at PASCOS 94, 11 Pages, 2 figures, Latex, epsf.tex, SLAC--PUB--664

Creation of a scalar potential in 2D dilaton gravity

We investigate quantum corrections of the 2-d dilaton gravity near the singularity. Our motivation comes from a s-wave reduced cosmological solution which is classically singular in the scalar fields (dilaton and moduli). As result we find, that the singularity disappears and a dilaton/moduli potential is created.Comment: talk presented at MG 7, 4 Pages, latex, SLAC-PUB-667

Supersymmetric Intersecting D6-Branes and Fluxes in Massive Type IIA String Theory

We study N=1 supersymmetric four-dimensional solutions of massive Type IIA supergravity with intersecting D6-branes in the presence NS-NS three-form fluxes. We derive N=1 supersymmetry conditions for the D6-brane and flux configurations in an internal manifold X6 and derive the intrinsic torsion (or SU(3)-structure) related to the fluxes. In the absence of fluxes, N=1 supersymmetry implies that D6-branes wrap supersymmetric three-cycles of X6 that intersect at angles of SU(3) rotations and the geometry is deformed by SU(3)-structures. The presence of fluxes breaks the SU(3) structures to SU(2) and the D6-branes intersect at angles of SU(2) rotations; non-zero mass parameter corresponds to D8-branes which are orthogonal to the common cycle of all D6-branes. The anomaly inflow indicates that the gauge theory on intersecting (massive) D6-branes is not chiral

Topological Objects in 5D Maxwell Einstein Supergravity

In this letter is shown that it is possible to obtain scalar hypersurfaces in 5D N=2 SUGRA where the allowed regions with positive definite scalar metric have a non-trivial topology. This situation may aid in the construction of domain wall solutions which confine gravity to 4 dimensions.Comment: 8 pages, 8 figures, accepted in PLB, reference adde

Singular 7-manifolds with G(2) holonomy and intersecting 6-branes

A 7-manifold with G(2) holonomy can be constructed as a R-3 bundle over a quaternionic space. We consider a quaternionic base space which is singular and its metric depends on three parameters, where one of them corresponds to an interpolation between S-4 and CP2 or its non-compact analogs. This 4d Einstein space has four isometrics and the fixed point set of a generic Killing vector is discussed. When embedded into M-theory the compactification over a given Killing vector gives intersecting 6-branes as IIA configuration and we argue that membrane instantons may resolve the curvature singularit