Cosmological Spacetimes from Negative Tension Brane Backgrounds

We identify a time-dependent class of metrics with potential applications tocosmology, which emerge from negative-tension branes. The cosmology is based ona general class of solutions to Einstein-dilaton-Maxwell theory, presented in{hep-th/0106120}. We argue that solutions with hyperbolic or planar symmetrydescribe the gravitational interactions of a pair of negative-tension$q$-branes. These spacetimes are static near each brane, but becometime-dependent and expanding at late epoch -- in some cases asymptoticallyapproaching flat space. We interpret this expansion as being the spacetime'sresponse to the branes' presence. The time-dependent regions provide explicitexamples of cosmological spacetimes with past horizons and no past nakedsingularities. The past horizons can be interpreted as S-branes. We prove thatthe singularities in the static regions are repulsive to time-like geodesics,extract a cosmological `bounce' interpretation, compute the explicit charge andtension of the branes, analyse the classical stability of the solution (inparticular of the horizons) and study particle production, deriving a generalexpression for Hawking's temperature as well as the associated entropy.Comment: 43 pages, 8 figures. Published versio