Inflation and preheating in nonoscillatory models - art. no. 103505

We study inflationary models in which the effective potential of the inflat on field does not have a minimum, but rather gradually decreases at large p hi. In such models the inflaton field does not oscillate after inflation, a nd its effective mass becomes vanishingly small, so the standard theory of reheating based on the decay of the oscillating inflaton field does not app ly. For a long time the only mechanism of reheating in such nonoscillatory (NO) models was based on gravitational particle production in an expanding universe. This mechanism is very inefficient. We will show that it may lead to cosmological problems associated with large isocurvature fluctuations a nd overproduction of dangerous relies such as gravitinos and moduli fields. We also note that the setting of initial conditions for the stage of rehea ting in these models should be reconsidered. All of these problems can be r esolved in the context of the recently proposed scenario of instant preheat ing if there exists an interaction g(2)phi(2)chi(2) of the inflaton field p hi with another scalar field chi. We show that the mechanism of instant pre heating in NO models is much more efficient than the usual mechanism of gra vitational particle production even if the coupling constant g(2) is extrem ely small, 10(-14) much less than g(2) much less than 1. [S0556-2821(99)083 18-6].