De Sitter braneworld and gravitational waves

TL;DR

This paper explores a braneworld model with multiple scalar fields and an infinite extra dimension, demonstrating a de Sitter solution for early universe inflation and analyzing gravitational wave modes, including massless and massive gravitons.

Contribution

It introduces a multi-scalar field braneworld model with a de Sitter background and analyzes the spectrum of gravitational waves, including conditions for localizable massive modes.

Findings

Massless graviton mode is localizable on the brane.

Massive modes form a continuous spectrum with a mass gap.

Gravitational wave evolution differs significantly between massless and massive modes.

Abstract

We study the braneworld theory constructed by multi scalar fields. The model contains a smooth and infinitely large extra dimension, allowing the background fields propagating in it. We give a de Sitter solution for the four-dimensional cosmology as a good approximation to the early universe inflation. We show that the graviton has a localizable massless mode, and a series of continuous massive modes, separated by a mass gap. There could be a normalizable massive mode, depending on the background solution. The gravitational waves of massless mode evolve the same as the four dimensional theory, while that of the massive modes evolve greatly different from the massless mode.