Constraints on variations in inflaton decay rate from modulated
  preheating
  Modulated (p)reheating is thought to be an alternative mechanism for
producing super-horizon curvature perturbations in CMB. But large
non-gaussianity and iso-curvature perturbations produced by this mechanism rule
out its acceptability as the sole process responsible for generating CMB
perturbations. We explore the situation where CMB perturbations are mostly
generated by usual quantum fluctuations of inflaton during inflation, but a
modulated coupling constant between inflaton and a secondary scalar affects the
preheating process and produces some extra curvature perturbations. If the
modulating scalar field is considered to be a dark matter candidate, coupling
constant between the fields has to be unnaturally fine tuned in order to keep
the local-form non-gaussianity and the amplitude of iso-curvature perturbations
within observational limit; otherwise parameters of the models have to be
tightly constrained. Those constraints imply that the curvature perturbations
generated by modulated preheating should be less than 15% of the total observed
CMB perturbations. On the other hand if the modulating scalar field is not a
dark matter candidate, parameters of the models could not be constrained, but
the constraints on the maximum amount of the curvature perturbations coming
from modulated preheating remain valid.
