Gravitational waves from first order phase transitions during inflation

TL;DR

This paper investigates the characteristics and detectability of gravitational waves generated by first order phase transitions during inflation, highlighting their potential signatures in the CMBR and future gravitational wave detectors.

Contribution

It provides a comprehensive analysis of gravitational wave production during inflationary phase transitions, emphasizing the dominant bubble collision source and the observational prospects.

Findings

Bubble collisions are the main source of gravitational waves during inflation.

Detectable signals can appear in the CMBR and with future detectors like DECIGO.

The spectrum's features depend on the transition rate and number of phase transitions.

Abstract

We study the production, spectrum and detectability of gravitational waves in models of the early Universe where first order phase transitions occur during inflation. We consider all relevant sources. The self-consistency of the scenario strongly affects the features of the waves. The spectrum appears to be mainly sourced by collisions of bubble of the new phases, while plasma dynamics (turbulence) and the primordial gauge fields connected to the physics of the transitions are generally subdominant. The amplitude and frequency dependence of the spectrum for modes that exit the horizon during inflation are different from those of the waves produced by quantum vacuum oscillations of the metric or by first order phase transitions not occurring during inflation. A moderate number of slow (but still successful) phase transitions can leave detectable marks in the CMBR, but the signal weakens rapidly for faster transitions. When the number of phase transitions is instead large, the primordial gravitational waves can be observed both in the CMBR or with LISA (marginally) and especially DECIGO. We also discuss the nucleosynthesis bound and the constraints it places on the parameters of the models.