No Large Scale Curvature Perturbations during Waterfall of Hybrid
  Inflation
  In this paper the possibility of generating large scale curvature
perturbations induced from the entropic perturbations during the waterfall
phase transition of standard hybrid inflation model is studied. We show that
whether or not appreciable amounts of large scale curvature perturbations are
produced during the waterfall phase transition depend crucially on the
competition between the classical and the quantum mechanical back-reactions to
terminate inflation. If one considers only the classical evolution of the
system we show that the highly blue-tilted entropy perturbations induce highly
blue-tilted large scale curvature perturbations during the waterfall phase
transition which dominate over the original adiabatic curvature perturbations.
However, we show that the quantum back-reactions of the waterfall field
inhomogeneities produced during the phase transition dominate completely over
the classical back-reactions. The cumulative quantum back-reactions of very
small scales tachyonic modes terminate inflation very efficiently and shut off
the curvature perturbations evolution during the waterfall phase transition.
This indicates that the standard hybrid inflation model is safe under large
scale curvature perturbations during the waterfall phase transition.
