We study chaotic dynamics in preheating after inflation in which an inflaton φ is coupled to another scalar field χ through an interaction. We first estimate the size of the quasi-homogeneous field χ at the beginning of reheating for large-field inflaton potentials V(φ) ≤ V 0φn 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 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 g2/λ ≫ 1.
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