General relativistic effects in preheating

General relativistic effects in the form of metric perturbations are usuall y neglected in the preheating era that follows inflation. We argue that in realistic multi-field models these effects are in fact crucial, and the ful ly coupled system of metric and quantum field fluctuations needs to be cons idered. Metric perturbations are resonantly amplified, breaking the scale-i nvariance of the primordial spectrum, and in turn stimulate scalar field re sonances via gravitational rescattering. This non-gravitationally dominated nonlinear growth of gravitational fluctuations may have significant effect s on the Doppler peaks in the cosmic background radiation, primordial black hole formation, gravitational waves and nonthermal symmetry restoration. ( C) 1999 Elsevier Science B.V. All rights reserved.