Lattice Simulations of Axion-U(1) Inflation

TL;DR

This paper introduces the first nonlinear lattice simulation of axion-U(1) inflation, revealing how non-Gaussianity evolves and impacts primordial black hole bounds and gravitational wave signals.

Contribution

It demonstrates the importance of high-order statistics in linear regimes and the suppression of non-Gaussianity in nonlinear dynamics, establishing lattice simulations as a key tool for inflation studies.

Findings

High-order statistics are essential in the linear regime.

Non-Gaussianity is suppressed during nonlinear evolution.

Results relax bounds on primordial black hole overproduction.

Abstract

We present the first nonlinear lattice simulation of an axion field coupled to a U(1) gauge field during inflation. We use it to fully characterize the statistics of the primordial curvature perturbation {\zeta}. We find high-order statistics to be essential in describing non-Gaussianity of {\zeta} in the linear regime of the theory. On the contrary, non-Gaussianity is suppressed when the dynamics becomes nonlinear. This relaxes bounds from overproduction of primordial black holes, allowing for an observable gravitational waves signal at pulsar timing array and interferometers scales. Our work establishes lattice simulations as a crucial tool to study the inflationary epoch and its predictions.