On graviton production in braneworld cosmology

TL;DR

This paper investigates graviton production in a five-dimensional braneworld model, demonstrating that massive modes decouple and the four-dimensional graviton behaves as expected in a low-energy, radiation-dominated universe.

Contribution

It shows that in a braneworld cosmology, massive Kaluza-Klein modes decouple and the four-dimensional graviton remains unaffected by the brane's motion at late times.

Findings

Massive Kaluza-Klein modes do not get generated.

The four-dimensional graviton obeys standard equations at low energy.

Massive modes decouple as the regulator brane moves to infinity.

Abstract

We study braneworlds in a five dimensional bulk, where cosmological expansion is mimicked by motion through AdS$_5$. We show that the five dimensional graviton reduces to the four dimensional one in the late time approximation of such braneworlds. Inserting a fixed regulator brane far from the physical brane, we investigate quantum graviton production due to the motion of the brane. We show that the massive Kaluza-Klein modes decouple completely from the massless mode and they are not generated at all in the limit where the regulator brane position goes to infinity. In the low energy limit, the massless four dimensional graviton obeys the usual 4d equation and is therefore also not generated in a radiation-dominated universe.