Preheating of the nonminimally coupled inflaton field

We investigate preheating of an inflaton field (Formula presented) coupled nonminimally to a spacetime curvature by the method of Hartree approximations. In the case of a self-coupling inflaton potential (Formula presented) the dynamics of preheating changes by the effect of the negative (Formula presented) We find that the nonminimal coupling works in two ways. First, since the initial value of the inflaton field for reheating becomes smaller with the increase of (Formula presented) the evolution of the inflaton quanta is delayed for fixed (Formula presented) Second, the oscillation of the inflaton field is modified and the nonadiabatic change around (Formula presented) occurs significantly. That makes the resonant band of the fluctuation field wider. Especially for strong coupling regimes (Formula presented) the growth of the inflaton fluctuation is dominated by the resonance due to the nonminimal coupling, which leads to a significant enhancement of low momentum modes. Although the final variance of the inflaton fluctuation does not change significantly compared with the minimally coupled case, we have found that the energy transfer from the homogeneous inflaton to created particles efficiently occurs for (Formula presented)