Inflation after preheating

Preheating after inflation may lead to non-thermal phase transitions with s ymmetry restoration. These phase transitions may occur even if the total en ergy density of fluctuations produced during reheating is relatively small as compared with the vacuum energy in the state with restored symmetry. As a result, in some inflationary models one encounters a secondary, non-therm al stage of inflation due to symmetry restoration after preheating. We revi ew the theory of non-thermal phase transitions and make a prediction about the expansion factor during the secondary inflationary stage. We then prese nt the results of lattice simulations which verify these predictions, and d iscuss possible implications of our results for the theory of formation of topological defects during non-thermal phase transitions.