Graviton emission from the brane in the bulk in a model with extra dimension

TL;DR

This paper investigates graviton emission from a brane in a five-dimensional model, calculating its spectrum and effects on cosmology, and finds that graviton production has negligible impact on primordial nucleosynthesis.

Contribution

It provides a detailed perturbative calculation of graviton emission and its minimal influence on cosmological processes in brane-world models.

Findings

Graviton emission spectrum is computed for late cosmology.

Corrections to Einstein equations due to graviton production are small.

Primordial helium abundance is unaffected by graviton emission.

Abstract

In a model of 3-brane embedded in 5D space-time we calculate the graviton emission from the brane to the bulk. Matter is confined to the brane, gravitons produced in reactions of matter on the brane escape to the bulk. The Einstein equations which are modified by the terms due to graviton production are solved perturbatively, the leading order being that without the graviton production. In the period of late cosmology, in which in the generalized Friedmann equation the term linear in the energy density of matter in dominant, we calculate the spectrum of gravitons (of the tower of Kaluza-Klein states) and the collision integral in the Boltzmann equation. We find the energy-momentum tensor of the emitted gravitons in the bulk, and using it show that corrections due to graviton production to the leading-order terms in the Einstein equations are small, and the perturbative approach is justified. We calculate the difference of abundances of ${}^4 He$ produced in primordial nucleosynthesis in the models with and without the graviton production, and find that the difference is a very small number, much smaller than that estimated previously.