Preheating of the nonminimally coupled inflaton field

TL;DR

This paper studies how nonminimal coupling of the inflaton field to spacetime curvature affects preheating, revealing that strong negative coupling enhances resonance and energy transfer during the reheating phase.

Contribution

It demonstrates the impact of nonminimal coupling on preheating dynamics, especially how negative coupling broadens resonance bands and enhances particle production.

Findings

Negative nonminimal coupling delays inflaton evolution.

Resonance bands become wider with stronger coupling.

Efficient energy transfer occurs for coupling 0.

Abstract

We investigate preheating of an inflaton field $\phi$ coupled nonminimally to a spacetime curvature. In the case of a self-coupling inflaton potential $V(\phi)=\lambda \phi^4/4$, the dynamics of preheating changes by the effect of the negative $\xi$. We find that the nonminimal coupling works in two ways. First, since the initial value of inflaton field for reheating becomes smaller with the increase of $|\xi|$, the evolution of the inflaton quanta is delayed for fixed $\lambda$. Second, the oscillation of the inflaton field is modified and the nonadiabatic change around $\phi=0$ occurs significantly. That makes the resonant band of the fluctuation field wider. Especially for strong coupling regimes $|\xi| \gg 1$, the growth of the inflaton flutuation is dominated by the resonance due to the nonminimal coupling, which leads to the significant enhancement of low momentum modes. Although the final variance of the inflaton fluctuation does notchange significantly compared with the minimally coupled case, we have found that the energy transfer from the homogeneous inflaton to created particles efficiently occurs for $\xi<-60$.