Baryogenesis via relativistic bubble expansion

TL;DR

This paper introduces a new baryogenesis mechanism involving heavy particles created or gaining mass during relativistic bubble expansion in a first order phase transition, which can produce the matter-antimatter asymmetry with detectable gravitational waves.

Contribution

It proposes a novel baryogenesis process leveraging relativistic bubble expansion and heavy particle decay, with potential gravitational wave signatures, expanding beyond traditional electroweak baryogenesis models.

Findings

Mechanism works with high reheat temperatures ($\gtrsim 10^{10}$ GeV).

Supercooling allows for lower reheat temperatures ($\sim 10^{6}$ GeV).

Potential gravitational wave signals at frequencies beyond upcoming detectors.

Abstract

We present a novel baryogenesis mechanism in which the asymmetry is sourced from heavy particles which either gain their mass or are created during bubble expansion in a strong first order phase transition. These particles then decay in a CP and baryon number violating way inside the bubble. The particles are inherently out-of-equilibrium and sufficiently dilute after wall crossing so the third Sakharov condition is easily met. Washout is avoided provided the reheat temperature is sufficiently below the scale of the heavy particles. The mechanism relies on moderate supercooling and relativistic walls which -- in contrast to electroweak baryogenesis -- generically leads to a sizable gravitational wave signal, although in the simplest realisations at frequencies beyond upcoming detectors. We present a simple example model and discuss the restrictions on the parameter space for the mechanism to be successful. We find that high reheat temperatures $T_{\rm RH} \gtrsim 10^{10}$ GeV are generally preferred, whereas stronger supercooling allows for temperatures as low as $T_{\rm RH} \sim 10^{6}$ GeV, provided the vacuum energy density is sufficiently suppressed. We briefly comment on using resonantly enhanced CP violation to achieve even lower scales.