Heterogeneous Cosmological Phase Transitions: Seeded by Domain Walls and Junctions

TL;DR

This paper investigates how preexisting domain walls and junctions influence cosmological first-order phase transitions, revealing that junction-seeded nucleation can dominate and occur at higher temperatures than homogeneous processes.

Contribution

It introduces a detailed analysis of domain wall and junction seeded nucleation, showing their significant impact on the dynamics and completion of cosmological phase transitions.

Findings

Junction-seeded nucleation occurs at higher temperatures than homogeneous nucleation.

Larger domain-wall tension reduces the nucleation volume and critical action.

Junctions seed nucleation more efficiently than walls alone.

Abstract

Heterogeneous nucleation is central to many familiar first-order phase transitions such as the freezing of water and the solidification of metals, and it can also play a crucial role in cosmology. We examine nucleation seeded by preexisting domain walls and demonstrate its strong impact on the dynamics of cosmological phase transitions. The bubble solutions take the form of spherical caps, and the contact angle is fixed by the ratio of the domain-wall tension to the bubble-wall tension. A larger domain-wall tension, or equivalently a smaller contact angle, reduces the wall-seeded bubble volume and lowers the critical nucleation action. For theories with $\mathbb{Z}_{n\geq 3}$ symmetry, domain-wall junctions naturally appear and we find that they seed nucleation even more efficiently than the walls themselves. Using a two-scalar-field model as an illustration, we compute nucleation temperatures for both homogeneous and heterogeneous channels and show that junction-seeded nucleation occurs at a higher temperature and is the dominant mechanism that completes the first-order cosmological phase transition.