Thermal Effects and Sudden Decay Approximation in the Curvaton Scenario
  We study the impact of a temperature-dependent curvaton decay rate on the
primordial curvature perturbation generated in the curvaton scenario. Using the
familiar sudden decay approximation, we obtain an analytical expression for the
curvature perturbation after the decay of the curvaton. We then investigate
numerically the evolution of the background and of the perturbations during the
decay. We first show that the instantaneous transfer coefficient, related to
the curvaton energy fraction at the decay, can be extended into a more general
parameter, which depends on the net transfer of the curvaton energy into
radiation energy or, equivalently, on the total entropy ratio after the
complete curvaton decay. We then compute the curvature perturbation and compare
this result with the sudden decay approximation prediction.
