Reheating the universe after multi-field inflation

Abstract

We study in detail (p)reheating after multi-field inflation models with a particularfocus on N-flation. We consider a variety of different couplings between the inflatonsand the matter sector, including both quartic and trilinear interactions with a lightscalar field. We show that the presence of multiple oscillating inflatons makes parametricresonance inefficient in the case of the quartic interactions. Moreover, perturbative processesdo not permit a complete decay of the inflaton for this coupling. In order to recover the hot bigbang, we must instead consider trilinear couplings. In this case we show that strong nonperturbativepreheating is possible via multi-field tachyonic resonance. In addition, late-time perturbative effects do permita complete decay of the condensate. We also study the production of gauge fields for several prototype couplings, finding similar results to the trilinear scalar coupling. During the course of our analysiswe develop the mathematical theory of the quasi-periodic Mathieu equation, the multi-field generalizationof the Floquet theory familiar from preheating after single field inflation. We also elaborate on the theory ofperturbative decays of a classical inflaton condensate, which is applicable in single-field models also.