EXPONENTIAL GROWTH OF PARTICLE NUMBER FAR FROM THE PARAMETRIC RESONANCE

It is known that exponential particle creation can occur in situations which do not fall in the parametric resonance regime characterized by oscillations of the inflaton field about its minimum. Here we present a new analytical approach to exponential particle production which can occur when the inflaton is far from the minimum of its potential. Crucial for this effect is a term in the equation of motion which acts like a negative mass term, as occurs for tachyonic preheating and negative coupling particle production. Our techniques can be applied in models with a strong coupling between matter fields χ and the inflaton ϕ, or in some models in which the inflaton has a large amplitude of oscillation. On the other hand our analysis yields results which are quite model dependent. Although our analysis is general, in order to be clear we specialize, in this paper, to the model with interaction Lagrangian -g M_plϕχ².