NONTHERMAL PHASE-TRANSITIONS AFTER INFLATION

At the first stage of reheating after inflation, parametric resonance may rapidly transfer most of the energy of an inflaton field phi to th e energy of other bosons. We show that quantum fluctuations of scalar and vector fields produced at this stage ar much greater than they wou ld be in a state of thermal equilibrium. This leads to cosmological ph ase transitions of a new type, which may result in a copious productio n of topological defects and in a secondary stage of inflation after r eheating.