Inflation and Brane Gases

TL;DR

This work introduces a string-inspired mechanism for bulk inflation driven by a gas of co-dimension one branes that are out of thermal equilibrium, with inflation occurring after the dilaton is stabilized. The key result is that a $d$-dimensional bulk experiences power-law inflation when $d=p+1$, with a finite duration set by the brane correlation length crossing the Hubble radius, and a potential e-folding count ${\cal N}$ that depends on fundamental scales. A central challenge is generating scale-invariant adiabatic perturbations and avoiding domain-wall overabundance and reheating problems, which the authors partially address by proposing stabilized embedded branes in Type IIB theory as a plausible route. The proposal also aims to connect with broader string cosmology ideas such as hierarchies of spatial dimensions and brane winding, offering a concrete, testable framework that ties early-universe inflation to intrinsic stringy brane dynamics, while signaling the need for further work on perturbations and post-inflation evolution.

Abstract

We investigate a new way of realizing a period of cosmological inflation in the context of brane gas cosmology. It is argued that a gas of co-dimension one branes, out of thermal equilibrium with the rest of the matter, has an equation of state which can - after stabilization of the dilaton - lead to power-law inflation of the bulk. The most promising implementation of this mechanism might be in Type IIB superstring theory, with inflation of the three large spatial dimensions triggered by ``stabilized embedded 2-branes''. Possible applications and problems with this proposal are discussed.