Measuring the Inflaton Coupling in the CMB
  We study the conditions under which simple relations between the inflaton
couplings and CMB observables can be established. The crucial criterion is to
avoid feedback effects during reheating, which tend to introduce a complicated
dependence of the CMB observables on a large number of microphysical parameters
that prohibits the derivation of meaningful constraints on any individual one
of them. We find that the inflaton coupling can be "measured" with cosmological
data when the effective potential during reheating can be approximated by a
parabola, and when the coupling constants are smaller than an upper bound that
it determined by the ratios between the inflaton mass and the Planck mass or
the scale of inflation. The power at which these ratios appear is determined by
the power at which the inflaton appears in a given interaction term, and the
value of the upper bound is largely independent of the type of produced
particle. Our results show that next generation CMB observatories may be able
to constrain the inflaton couplings for various types of interactions,
providing an important clue to understand how a given model of inflation may be
embedded into a more fundamental microphysical theory of nature.
