A heatwave affair: mixed Higgs-$R^2$ preheating on the lattice

TL;DR

This paper uses lattice simulations to study nonlinear preheating in Higgs-$R^2$ inflation, revealing detailed dynamics and potential observational signatures that distinguish it from other inflation models.

Contribution

First nonlinear lattice study of preheating in $R^2$-like Higgs inflation, analyzing dynamics and observational implications.

Findings

Preheating begins with tachyonic Higgs boson production.

Scattering processes follow initial tachyonic production.

Predictions align with Planck data, but future 21 cm experiments could distinguish models.

Abstract

We use lattice methods to perform the first nonlinear study of preheating in $R^2$-healed Higgs inflation for "$R^2$-like" parameters $1.1\times 10^9$ and $1.8\times 10^9$ where the curvature-squared coupling $\beta$ and nonminimal coupling $\xi$ of the Higgs field contribute similarly to the CMB scalar perturbations. Preheating occurs first through tachyonic production of Higgs bosons, and later scattering off the homogeneous inflaton field. We generalise our results to "Higgs-like" parameters with smaller $\beta$, where observables saturate the bound of instantaneous preheating. All predictions for the spectral index and tensor-to-scalar ratio lie within the $1\sigma$ region of measurements by the Planck satellite, but a future ground-based experiment optimised for 21 cm tomography may be able to discriminate the mixed Higgs-curvature inflation from the pure Higgs and $R^2$ theories.