Evolution of gravitational waves from inflationary brane-world : numerical study of high-energy effects

TL;DR

This paper numerically investigates how high-energy effects in brane-world cosmology influence gravitational wave evolution after inflation, revealing suppression due to Kaluza-Klein mode excitation and comparing results with low-energy approximations.

Contribution

It provides a quantitative numerical analysis of high-energy effects on gravitational waves in brane-world models, highlighting the impact of KK modes on wave amplitude.

Findings

KK modes cause suppression of gravitational wave amplitude

KK modes escape into the bulk, reducing on-brane GW signals

Numerical results agree with low-energy semi-analytic predictions

Abstract

We study the evolution of gravitational waves(GWs) after inflation in a brane-world cosmology embedded in five-dimensional anti-de Sitter spacetime. Contrary to the standard four-dimensional results, the GWs at the high-energy regime in brane-world model suffer from the effects of the non-standard cosmological expansion and the excitation of the Kaluza-Klein modes(KK-modes), which can affect the amplitude of stochastic gravitational wave background significantly. To investigate these two high-energy effects quantitatively, we numerically solve the wave equation of the GWs in the radiation dominated epoch at relatively low-energy scales. We show that the resultant GWs is suppressed by the excitation of the KK modes. The created KK modes are rather soft and escape away from the brane to the bulk gravitational field. The results are also compared to the semi-analytic prediction from the low-energy approximation and the evolved amplitude of GWs on the brane reasonably matches the numerical simulations.