Nonthermal phase transitions after inflation.

At the rst stage of reheating after in ation, parametric resonance may rapidly transfer most of the energy of an in aton eld to the energy of other bosons. We show that quantum uctuations of scalar and vector elds produced at this stage are much greater than they would be in a state of thermal equilibrium. This leads to cosmological phase transitions of a new type, which may result in a copious production of topological defects and in a secondary stage of in ation after reheating.