# Accelerating the Universe with Gravitational Waves

## TL;DR

This paper investigates how primordial gravitational waves influence the universe's expansion, revealing they can mimic dark energy during matter domination and act as a relativistic fluid during radiation domination.

## Contribution

It provides a detailed calculation of gravitational wave backreaction effects on cosmic expansion, highlighting their potential role as dark energy.

## Key findings

- Backreaction acts as a relativistic fluid during radiation domination.
- A small dark energy component with w=-8/9 emerges during matter domination.
- Primordial gravitational waves can significantly impact cosmic evolution.

## 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.