Cosmological Spacetimes from Negative Tension Brane Backgrounds

TL;DR

The paper addresses cosmologies sourced by negative-tension branes within Einstein-dilaton-Maxwell theory, constructing explicit time-dependent spacetimes with horizons that separate static near-brane regions from expanding cosmological interiors. It develops both a simple Schwarzschild-like seed and a general dilaton-generalized Maxwell-Einstein solution framework, characterized by harmonic functions h_± and charges Q, describing a pair of oppositely charged, negative-tension q-branes. The work analyzes horizon structure, charges and tensions, geodesic behavior, stability, particle production, and Hawking-like thermodynamics, and demonstrates that the asymptotic regions can be flat while the near-horizon region exhibits a universal geometry. These models provide tractable, horizon-containing cosmologies with potential links to S-branes and orientifold-like negative-tension objects, offering insights into early-universe dynamics and causal structure in the presence of negative tension.

Abstract

We identify a time-dependent class of metrics with potential applications to cosmology, which emerge from negative-tension branes. The cosmology is based on a general class of solutions to Einstein-dilaton-Maxwell theory, presented in {hep-th/0106120}. We argue that solutions with hyperbolic or planar symmetry describe the gravitational interactions of a pair of negative-tension $q$-branes. These spacetimes are static near each brane, but become time-dependent and expanding at late epoch -- in some cases asymptotically approaching flat space. We interpret this expansion as being the spacetime's response to the branes' presence. The time-dependent regions provide explicit examples of cosmological spacetimes with past horizons and no past naked singularities. The past horizons can be interpreted as S-branes. We prove that the singularities in the static regions are repulsive to time-like geodesics, extract a cosmological `bounce' interpretation, compute the explicit charge and tension of the branes, analyse the classical stability of the solution (in particular of the horizons) and study particle production, deriving a general expression for Hawking's temperature as well as the associated entropy.