Graviton Emission into Non-Z_2 Symmetric Brane World Spacetimes

TL;DR

This paper models graviton emission in non-Z_2 symmetric brane worlds using an AdS-Vaidya approximation, revealing complex effects on dark radiation and potential universe collapse.

Contribution

It derives evolution equations for graviton emission in non-Z_2 symmetric brane worlds and analyzes the impact on dark radiation and universe stability.

Findings

Graviton emission generally reduces non-Z_2 symmetry.

Dark radiation can increase, decrease, or become negative due to asymmetry.

Negative dark radiation can lead to brane universe collapse.

Abstract

The equations for the evolution of a homogeneous brane world that emits gravitons at early times, and into a non-Z_2 symmetric bulk, are derived using an AdS-Vaidya spacetime approximation. The behaviour of the black hole mass parameters either side of the brane is analysed, and it is found that in general graviton emission leads to a decrease in the non-Z_2 symmetry. However, the behaviour of the dark radiation term in the Friedmann equation is more complex: it is shown that this term can increase or decrease due to the non-Z_2 symmetry, and can become negative in some cases, leading to H=0 and the brane universe collapsing. Constraints on the initial (nonzero) sizes of the mass parameters are therefore derived.