Non-perturbative approach for scalar particle production in Higgs-$R^2$ inflation

TL;DR

This paper studies how scalar particles are produced during Higgs-$R^2$ inflation, especially focusing on non-perturbative effects and the influence of mass and coupling on production rates.

Contribution

It provides a detailed non-perturbative analysis of scalar particle production in Higgs-$R^2$ inflation, including numerical solutions and the impact of different couplings and masses.

Findings

Particle production occurs for light particles with conformal coupling.

Massive particles with $m_\chi > M/2$ are also produced.

Non-perturbative effects significantly influence particle densities.

Abstract

We investigate the non-perturbative production of scalar particles within the Higgs-$R^2$ inflation model, focusing on a massive spectator field that interacts gravitationally via a non-minimal coupling to the Ricci scalar $R$. By transforming the model to the Einstein frame, where direct couplings between inflationary dynamics and the spectator field emerge, we analyze both perturbative and non-perturbative particle production. We solve the spectator field equation numerically, using the Bogolyubov transformation, to calculate the comoving particle density. Our findings indicate that particle production occurs for light particles with conformal coupling and for masses $m_\chi > M/2$ in the minimally coupled scenario.