Suppression of parametric resonance and the viability of tachyonic preheating after multifield inflation

We investigate the feasibility of explosive particle production via parametric resonance or tachyonic preheating in multifield inflationary models by means of lattice simulations. We observe a strong suppression of resonances in the presence of four-leg interactions between the inflaton fields and a scalar matter field, leading to insufficient preheating when more than two inflatons couple to the same matter field. This suppression is caused by a dephasing of the inflatons that increases the effective mass of the matter field. Including three-leg interactions leads to tachyonic preheating, which is not suppressed by an increase in the number of fields. If four-leg interactions are subdominant, we observe a slight enhancement of tachyonic preheating. Thus, in order for preheating after multifield inflation to be efficient, one needs to ensure that three-leg interactions are present. If no tachyonic contributions exist, we expect the old theory of reheating to be applicable.