Notes on SU(3) Structures in Type IIB Supergravity

We study solutions of type IIB supergravity with an SU(3) structure group and four dimensional Poincare invariance and present relations among the bosonic fields which follow from the supersymmetry variations. We make explicit some results which also follow from the more general case of an SU(2) structure and give some short comments applicable to general supersymmetric solutions. We also provide simplified relations appropriate for duals of gauge theory renormalization group flows, and use these to derive the supergravity solution for a bound state of (p,q)5-branes and D3-branes.Comment: 14p, JHEP3.cls, v2 typos corrected, refs adde

Towards A Nonsingular Tachyonic Big Crunch

We discuss an effective field theory background containing the gravitational field, the dilaton and a closed string tachyon, and couple this background to a gas of fundamental strings and D strings. Allowing for the possibility of a non-vanishing dilaton potential of Casimir type, we demonstrate the possibility of obtaining a nonsingular, static tachyon condensate phase with fixed dilaton. The time reversal of our solution provides a candidate effective field theory description of a Hagedorn phase of string gas cosmology with fixed dilaton.Comment: 7 pages, two references adde

Backreaction in Closed String Tachyon Condensation

We consider backreaction due to production of massless strings in the background of a condensing closed string tachyon. Working in the region of weak tachyon, we find the modified equations of motion for massless strings with conformal perturbation theory. We solve for the positive and negative frequency modes and estimate the backreaction on the background dilaton. In large (supercritical) dimensions, we find that the backreaction can be significant in a large region of spacetime. We work with the bosonic string, but we expect these results to carry over into the heterotic case.Comment: 15 pg, 2 figures; v2. corrected eq of motion (does not substantially change conclusions), other minor changes; v3. minor changes, to be published in JHE