Probing Exotic Phases Via Stochastic Gravitational Wave Spectra

TL;DR

This paper explores how stochastic gravitational wave backgrounds from the early universe can reveal exotic phases, like phase transitions, through spectral distortions detectable by future GW observatories.

Contribution

It demonstrates that changes in the universe's equation of state due to massive particles can produce observable features in GW spectra, using a specific phase transition model as an example.

Findings

Massive particles cause a 20% dip in GW spectrum.

Future GW detectors could observe these spectral distortions.

Spectral features can probe early universe phase transitions.

Abstract

Stochastic backgrounds of gravitational waves (GWs) from the pre-BBN era offer a unique opportunity to probe the universe beyond what has already been achieved with the Cosmic Microwave Background (CMB). If the source is short in duration, the low frequency tail of the resulting GW spectrum follows a universal frequency scaling dependent on the equation of state of the universe when modes enter the horizon. We demonstrate that the distortion of the equation of state due to massive particles becoming non-relativistic can lead to an observable dip in the GW spectrum. To illustrate this effect, we consider a first order chiral symmetry breaking phase transition in the weak-confined Standard Model (WCSM). The model features a large number of pions and mostly elementary fermions with masses just below the critical temperature for the phase transition. These states lead to a 20$\%$ dip in the GW power. We find potential sensitivity to the distortions in the spectrum to future GW detectors such as LISA, DECIGO, BBO, and $\mu$Ares.