INFLATON DECAY AND HEAVY-PARTICLE PRODUCTION WITH NEGATIVE COUPLING

We study the decay of the inflaton in a general Z(2)xZ(2) symmetric tw o scalar theory. Since the dynamics of the system is dominated by stat es with large occupation numbers which admit a semiclassical descripti on, the decay can be studied by solving the classical equations of mot ion on the lattice. Of particular interest is the case when the cross coupling between the inflaton and the second scalar field is negative, which is naturally allowed in many realistic models. While the inflat on decays via parametric resonance in the positive coupling cast: we f ind that fur negative coupling there is a new mechanism of particle pr oduction which we call negative coupling instability. Because of this new mechanism the variances of the fields grow significantly larger be fore the production is shut off by the back reaction of the created pa rticles which could have important consequences for symmetry restorati on by nonthermal phase transitions. We also find that heavy particles are produced much more efficiently with negative coupling, which is of prime importance for GUT baryogenesis. Using a simple toy model for b aryogenesis and the results of our lattice simulations we show that fo r natural values of the cross coupling enough 10(14) GeV bosons are cr eated to produce a baryon to entropy ratio consistent with observation . This is to be contrasted with the situation for positive coupling, w here the value of the cross coupling required to produce such massive particles is technically unnatural. In addition to our numerical resul ts we obtain analytical estimates for the maximum variances of the fie lds in atr expanding universe for all cases of interest: massive and m assless inflaton, positive and negative cross coupling, with and witho ut significant self-interactions for the second field. [S0556-2821(97) 05722-6].