Preheating in derivatively coupled inflation models

Abstract

We study preheating in theories where the inflaton couples derivatively to scalar and gaugefields. Such couplings may dominate in, for example, models of natural inflation, inwhich the flatness of the inflaton potential is related to an approximate shiftsymmetry of the inflaton. We compare our results with previously studied models withnon-derivative couplings. For sufficiently heavy scalar matter, parametric resonanceis ineffective in reheating the universe, because the couplings of the inflaton tomatter are very weak. If scalar matter fields are light, derivative couplings lead tolong-wavelength instabilities that drive matter fields to non-zero expectation values. Inthis case however, long-wavelength fluctuations of the light scalar are producedduring inflation, leading to a host of cosmological problems. In contrast, axion-likecouplings of the inflaton to a gauge field do not lead to production of long-wavelengthfluctuations during inflation. However, again because of the weakness of the couplingsto the inflaton, parametric resonance is not effective in producing gauge fieldquanta.