A Nearly Scale Invariant Spectrum of Gravitational Radiation from Global Phase Transitions

TL;DR

This paper calculates the gravitational wave spectrum from early universe global phase transitions, showing it is nearly scale invariant and potentially detectable, with amplitudes much larger than previously estimated.

Contribution

It provides an explicit calculation of the gravitational wave spectrum from global phase transitions using a large N sigma model approximation, highlighting its potential observational significance.

Findings

The spectrum is nearly scale invariant.

Amplitude can exceed naive estimates by over 3 orders of magnitude.

Transitions after inflation could dominate gravitational wave signals.

Abstract

Using a large N sigma model approximation we explicitly calculate the power spectrum of gravitational waves arising from a global phase transition in the early universe and we confirm that it is scale invariant, implying an observation of such a spectrum may not be a unique feature of inflation. Moreover, the predicted amplitude can be over 3 orders of magnitude larger than the naive dimensional estimate, implying that even a transition that occurs after inflation may dominate in Cosmic Microwave Background polarization or other gravity wave signals.