  We study the development of entropy fluctuations in brane inflation in a
warped throat, including the brane-antibrane tachyon as the waterfall field. We
find that there is a period at the end of inflation during which the entropy
mode associated with the tachyon field increases exponentially. In turn, the
induced entropy seeds a contribution to the curvature fluctuation on
cosmological scales which grows rapidly and could exceed the primordial
curvature perturbation. We identify parameter values for which in the absence
of back-reaction the induced curvature fluctuations are larger than the
primordial adiabatic ones. In the specific model we study, however,
back-reaction limits the growth of the entropy fluctuations. We discuss
situations in which back-reaction effects are less constraining. The lesson of
our investigation is that the study of the development of entropy fluctuations
at the end of the period of inflation can lead to constraints on models of
brane inflation and suggests that the curvaton mechanism may contribute
significantly to the spectrum of cosmological perturbations.
