  During inflationary preheating, the energy stored in the inflaton field is
rapidly converted into excitations of other entropy fields. This stage is
characterized by exponential particle production due to parametric resonance
and is notoriously difficult to analyze using analytic methods. We develop a
detailed numerical simulation to investigate inflationary preheating when the
potential of the inflaton is a power-law function with arbitrary power index.
To achieve a successful graceful exit from a primordial inflationary phase to a
smooth, oscillatory phase during preheating, we assume the inflaton potential
reduces to a quadratic function in the infrared regime, which may be regarded
as a mass term at low energy scales. With this simplification, our numerical
method may be applied to unconventional chaotic inflation models. To
demonstrate its validity, we numerically analyze the preheating stage of
axion-monodromy inflation which is inspired by string theory. By performing
perturbation analyses, our result shows that the power spectrum of primordial
curvature perturbation can be dominated by fluctuations of entropy field rather
than those of inflaton, which can be regarded as a particular realization of
the curvaton mechanism through a preheating process.
