Accelerating the Universe with Gravitational Waves

Abstract

Inflation generically produces primordial gravitational waves with a red spectral tilt. In this paper we calculate the backreaction produced by these gravitational waves on the expansion of the universe. We find that in radiation domination the backreaction acts as a relativistic fluid, while in matter domination a small dark energy emerges with an equation of state w=-8/9.

Comments: 18 pages, 4 figures. Replaced with version published by JCAP - some discussion and references added concerning second-order gravitational waves, typeset in JHEP style