  In a previous work we showed that large nongaussianities and
nonscale-invariant distortions in the CMB power spectrum can be generated in
hybrid inflation models, due to the contributions of the tachyon (waterfall)
field to the second order curvature perturbation. Here we clarify, correct, and
extend those results. We show that large nongaussianity occurs only when the
tachyon remains light throughout inflation, whereas n=4 contamination to the
spectrum is the dominant effect when the tachyon is heavy. We find constraints
on the parameters of warped-throat brane-antibrane inflation from
nongaussianity. For F-term and D-term inflation models from supergravity, we
obtain nontrivial constraints from the spectral distortion effect. We also
establish that our analysis applies to complex tachyon fields.
