No Large Scale Curvature Perturbations during Waterfall of Hybrid Inflation

TL;DR

This paper investigates whether large scale curvature perturbations are generated during the waterfall phase of hybrid inflation, concluding that quantum back-reactions prevent significant large scale perturbations, ensuring the model's safety.

Contribution

It demonstrates that quantum back-reactions dominate classical effects, preventing large scale curvature perturbations during the waterfall phase of hybrid inflation.

Findings

Quantum back-reactions shut off curvature perturbation growth.

Classical entropy perturbations induce blue-tilted curvature perturbations.

Hybrid inflation remains safe from large scale perturbations during waterfall.

Abstract

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.