Collision of Domain Walls and Reheating of the Brane Universe

Abstract

We study a particle production at the collision of two domain walls in 5-dimensional Minkowski spacetime. This may provide the reheating mechanism of an ekpyrotic (or cyclic) brane universe, in which two BPS branes collide and evolve into a hot big bang universe. We evaluate a production rate of particles confined to the domain wall. The energy density of created particles is given as $ρ\approx 20 \bar{g}^4 N_b ~m_η^4 $ where $\bar{g}$ is a coupling constant of particles to a domain-wall scalar field, $N_b $ is the number of bounces at the collision and $m_η$ is a fundamental mass scale of the domain wall. It does not depend on the width $d$ of the domain wall, although the typical energy scale of created particles is given by $ω\sim 1/d$. The reheating temperature is evaluated as $T_{\rm R}\approx 0.88 ~ \bar{g} ~ N_b^{1/4}$. In order to have the baryogenesis at the electro-weak energy scale, the fundamental mass scale is constrained as $m_η\gsim 1.1\times 10^7$ GeV for $\bar{g}\sim 10^{-5}$.