Geometric reheating of the Universe

TL;DR

This paper investigates the process of geometric preheating after inflation, analyzing how the inflaton transfers energy to a coupled scalar field under various conditions, using lattice simulations to explore non-linear effects and reheating efficiency.

Contribution

It extends the study of geometric preheating into the non-linear regime and assesses the viability of reheating for different inflationary potentials and parameters.

Findings

Reheating efficiency depends on the inflationary scale and potential power p.

For large scales, reheating is frustrated at p=2, partial at p=4, and efficient at p=6.

Self-interactions of the scalar field can block reheating unless very weak.

Abstract

We study the post-inflationary energy transfer from the inflaton ($\phi$) into a scalar field ($\chi$) non-minimally coupled to gravity through $\xi R|\chi|^2$, considering models with inflaton potential $V_{\rm inf} \propto |\phi|^{\,p}$ around $\phi = 0$. This corresponds to the paradigm of {\it geometric preheating}, which we extend to its non-linear regime via lattice simulations. Considering $\alpha$-attractor T-model potentials as a proxy, we study the viability of proper {\it reheating} for $p=2, 4, 6$, determining whether radiation domination (RD) due to energetic dominance of $\chi$ over $\phi$, can be achieved. For large inflationary scales $\Lambda$, reheating is frustrated for $p = 2$, it can be partially achieved for $p = 4$, and it becomes very efficient for $p = 6$. Efficient reheating can be however blocked if $\chi$ sustains self-interactions (unless these are extremely feeble), or if $\Lambda$ is low enough, so that inflaton fragmentation brings the universe rapidly into RD. Whenever RD is achieved, either due to reheating or to inflaton fragmentation, we characterize the energy and time scales of the problem, as a function of $\Lambda$ and $\xi$.