New twist to preheating - art. no. 043510

Metric perturbations typically strengthen field resonances during preheatin g. in contrast we present a model in which the super-Hubble field resonance s are completely suppressed when metric perturbations are included. The mod el is the nonminimal Fakir-Unruh scenario which is exactly solvable in the long-wavelength limit when metric perturbations are included, but exhibits exponential growth of super-Hubble modes in their absence. This gravitation ally enhanced integrability is exceptional, both for its rarity and for the power with which it illustrates the importance of including metric perturb ations in consistent studies of preheating. We conjecture a no-go result-th ere exists no single-field model with growth of cosmologically relevant met ric perturbations during preheating.