Inflationary electroweak/particle phase transitions and new classical gravitational waves on CMB

TL;DR

This paper explores how first-order particle phase transitions during inflation could produce classical, scale-dependent gravitational waves detectable in the CMB, offering new insights into early universe physics.

Contribution

It introduces the concept of inflationary particle phase transitions as a source of classical gravitational waves affecting the CMB, distinct from primordial vacuum fluctuations.

Findings

First-order inflationary phase transitions can generate low-frequency GWs.

Bubble dynamics produce scale-dependent B-mode spectra.

Electroweak phase transitions during inflation may relate to baryogenesis.

Abstract

Particle phase transitions in the early universe including electroweak and grand unification ones are well-studied subjects. We point out that there are new possible particle phase transitions around inflation. Those new inflationary particle phase transitions, if of the first order, may yield low-frequency gravitational waves (GWs) due to bubble dynamics, leaving imprints on the cosmic microwave background (CMB). In contrast to the nearly scale-invariant primordial GWs caused by vacuum fluctuation, these bubble-generated GWs are classical and have scale dependent B-mode spectra. If decoupled from inflaton, the electroweak phase transition during inflation may serve as a mirror image of the one after reheating where the baryon asymmetry could be generated via electroweak baryogenesis (EWBG). The second new electroweak phase transition may also be the source for EWBG.