Cosmic bubble and domain wall instabilities III: The role of oscillons in three-dimensional bubble collisions

TL;DR

This paper investigates how small initial fluctuations in bubble collisions during cosmic inflation can grow and lead to oscillon formation, breaking symmetry and producing observable gravitational wave signatures.

Contribution

It introduces the first detailed analysis of initial quantum fluctuation effects on bubble collision symmetry breaking and oscillon production using 3D simulations, including a two-field inflationary model.

Findings

Small initial perturbations grow and break SO(2,1) symmetry.

Oscillons are produced in bubble collisions with symmetry breaking.

Two-field models can produce inflation and oscillon formation simultaneously.

Abstract

We study collisions between pairs of bubbles nucleated in an ambient false vacuum. For the first time, we include the effects of small initial (quantum) fluctuations around the instanton profiles describing the most likely initial bubble profile. Past studies of this problem neglect these fluctuations and work under the assumption that the collisions posess an exact SO(2,1) symmetry. We use three-dimensional lattice simulations to demonstrate that for double-well potentials, small initial perturbations to this symmetry can be amplified as the system evolves. Initially the amplification is well-described by linear perturbation theory around the SO(2,1) background, but the onset of strong nonlinearities amongst the fluctuations quickly leads to a drastic breaking of the original SO(2,1) symmetry and the production of oscillons in the collision region. We explore several single-field models, and we find it is hard to both realize inflation inside of a bubble and produce oscillons in a collision. Finally, we extend our results to a simple two-field model. The additional freedom allowed by the second field allows us to construct viable inflationary models that allow oscillon production in collisions. The breaking of the SO(2,1) symmetry allows for a new class of observational signatures from bubble collisions that do not posess azimuthal symmetry, including the production of gravitational waves which cannot be supported by an SO(2,1) spacetime.