Effects of Fragmentation on Post-Inflationary Reheating

TL;DR

This paper investigates how the fragmentation of the inflaton condensate after inflation affects the reheating process, revealing that the impact varies depending on the decay channels and the nature of self-interactions.

Contribution

It provides a detailed analysis of the effects of condensate fragmentation on reheating, highlighting the dependence on the scalar potential shape and decay mechanisms.

Findings

Fragmentation can alter the reheating process, especially for $k \,\geq\, 4$.

Reheating via fermion decays is largely prevented by early fragmentation.

Reheating through boson decays or scatterings is less affected, with scatterings lowering the reheating temperature.

Abstract

We consider the effects of fragmentation on the post-inflationary epoch of reheating. In simple single field models of inflation, an inflaton condensate undergoes an oscillatory phase once inflationary expansion ends. The equation of state of the condensate depends on the shape of the scalar potential, $V(\phi)$, about its minimum. Assuming $V(\phi) \sim \phi^k$, the equation of state parameter is given by $w = P_\phi/\rho_\phi = (k-2)/(k+2)$. The evolution of condensate and the reheating process depend on $k$. For $k \ge 4$, inflaton self-interactions may lead to the fragmentation of the condensate and alter the reheating process. Indeed, these self-interactions lead to the production of a massless gas of inflaton particles as $w$ relaxes to 1/3. If reheating occurs before fragmentation, the effects of fragmentation are harmless. We find, however, that the effects of fragmentation depend sensitively to the specific reheating process. Reheating through the decays to fermions is largely excluded since perturbative couplings would imply that fragmentation occurs before reheating and in fact could prevent reheating from completion. Reheating through the decays to boson is relatively unaffected by fragmentation and reheating through scatterings results in a lower reheating temperature.