ar X iv : h ep - p h / 04 11 16 4 v 2 7 D ec 2 00 5 Chaotic dynamics in preheating after inflation

We study chaotic dynamics in preheating after inflation in which an inflaton φ is coupled to another scalar field χ through an interaction (1/2)gφχ. We first estimate the size of the quasihomogeneous field χ at the beginning of reheating for large-field inflaton potentials V (φ) = V0φ n by evaluating the amplitude of the χ fluctuations on scales larger than the Hubble radius at the end of inflation. Parametric excitations of the field χ during preheating can give rise to chaos between two dynamical scalar fields. For the quartic potential (n = 4, V0 = λ/4) chaos actually occurs for g/λ < O(10) in a linear regime before which the backreaction of created particles becomes important. This analysis is supported by several different criteria for the existence of chaos. For the quadratic potential (n = 2) the signature of chaos is not found by the time at which the backreaction begins to work, similar to the case of the quartic potential with g/λ ≫ 1.