Gravitational waves from cosmological phase transitions

TL;DR

This paper analyzes the generation of gravitational waves during cosmological first order phase transitions, focusing on their spectrum features and implications for early universe magnetic fields.

Contribution

It provides a simple explanation of gravitational wave spectrum features and assesses the impact of electroweak phase transition gravitational waves on seed magnetic fields.

Findings

Gravitational wave spectrum exhibits a $k^3$ growth on large scales.

The peak amplitude of gravitational waves can be estimated.

Nucleosynthesis bounds limit seed magnetic fields from the electroweak transition.

Abstract

I discuss the generation of a stochastic background of gravitational waves during a first order phase transition. I present simple general arguments which explain the main features of the gravitational wave spectrum like the $k^3$ power law growth on large scales and a estimate for the peak amplitude. In the second part I concentrate on the electroweak phase transition and argue that the nucleosynthesis bound on its gravitational wave background seriously limits seed magnetic fields which may have been generated during this transition.