Curvature perturbations from vacuum transition during inflation

TL;DR

This paper shows that vacuum transitions during inflation, involving a light scalar field, can generate large non-Gaussian features in the primordial curvature perturbation, which may be detectable.

Contribution

It introduces a numerical method to compute instanton solutions for vacuum tunnelling during inflation and analyzes their impact on non-Gaussianity in Higgs inflation.

Findings

Non-Gaussianity parameter $f_{NL}$ can reach order 10.

Vacuum transitions significantly affect curvature perturbations.

Method applicable to multi-minima scalar potentials.

Abstract

We demonstrate that in the presence of a light scalar spectator field, vacuum transitions taking place during inflation can produce large, potentially detectable non-Gaussian signatures in the primordial curvature perturbation. Such transitions are common in theories with multiple scalar fields when the potential has several minima. Our computation proceeds by numerically finding the instanton solution that describes quantum tunnelling between vacuum states in a de Sitter background, calculating its dependence on the spectator field and, thereby, its effect on the expansion of space. For a scenario with Higgs inflation, we obtain the non-Gaussianity parameter $f_\mathrm{NL} \sim O(10)$ and study its parameter dependence.