Collision of Domain Walls and Reheating of the Brane Universe

TL;DR

This paper investigates particle production during domain wall collisions in a 5D spacetime, proposing a reheating mechanism for brane cosmology that depends on collision dynamics and fundamental mass scales.

Contribution

It provides a quantitative analysis of particle production and reheating temperature in brane collision scenarios, linking microscopic parameters to cosmological outcomes.

Findings

Reheating temperature depends on coupling and collision parameters.

Particle production rate is independent of domain wall width.

Constraints on fundamental mass scale for baryogenesis are derived.

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 $\rho \approx 20 \bar{g}^4 N_b ~m_\eta^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 $m_\eta$ 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 $\omega\sim 1/d$. 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 $m_\eta \gsim 1.1\times 10^7$ GeV for $\bar{g}\sim 10^{-5}$.