Simulating first-order phase transition during inflation

TL;DR

This paper proposes a novel first-order phase transition mechanism during Starobinsky inflation at the GUT scale, using a dynamic potential barrier to control bubble nucleation, and confirms its effectiveness through lattice simulations and gravitational wave predictions.

Contribution

It introduces a new model of first-order phase transition during inflation with a dynamic potential barrier, enabling controlled bubble nucleation at the end of inflation.

Findings

Successful simulation of GUT-scale FoPT during Starobinsky inflation

Reproduction of analytical gravitational wave spectrum with oscillation features

Demonstration of controlled bubble nucleation timing during inflation

Abstract

Ending the inflation by vacuum decay is considered infeasible due to the graceful exit problem. Even if considering an alternative field other than the inflaton to realize a first-order phase transition (FoPT) during inflation, it is usually challenging for concrete model building, as bubble nucleations might not be fast and dense enough to successfully end the inflation. In this work, we propose a FoPT at the grand-unification-theory (GUT) scale within the Starobinsky inflation. The key construction is an exponentially evolving potential barrier dynamically controlled by the rolling inflaton, so that almost no bubble is nucleated during the early inflationary era, but with massive bubble nucleations near the end of inflation. With lattice numerical simulations, we have successfully tested this GUT-FoPT during Starobinsky inflation, and the resulting gravitational-wave energy density spectrum reproduces previous analytical estimation with a distinctive oscillation feature at high frequencies.