Lattice simulations of axion-U(1) inflation

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 become nonlinear. This relaxes the bounds from overproduction of primordial black holes, allowing for an observable gravitational waves signal at pulsar timing array and interferometer scales. Our work establishes lattice simulations as a crucial tool to study the inflationary epoch and its predictions.

Automated summary

We present the first nonlinear lattice simulation of the axion field coupled to a U(1) gauge field during inflation, and use it to fully characterize the statistics of the primordial curvature perturbation ζ. We find that high-order statistics are crucial in describing the non-Gaussianity of ζ in the linear regime of the theory, but non-Gaussianity is suppressed in the nonlinear dynamics. This relaxation of bounds allows for an observable gravitational wave signal at pulsar timing array and interferometer scales. Our work establishes lattice simulations as a crucial tool in studying the inflationary epoch and its predictions.