Entropy Fluctuations in Brane Inflation Models

TL;DR

This paper investigates how entropy fluctuations develop in brane inflation models, especially focusing on the tachyon field, and explores their impact on cosmological perturbations and model constraints.

Contribution

It analyzes the exponential growth of entropy modes during the end of inflation and assesses back-reaction effects on curvature fluctuation contributions in brane inflation.

Findings

Entropy mode associated with tachyon increases exponentially at inflation's end.

Induced entropy fluctuations can surpass primordial curvature perturbations.

Back-reaction limits the growth of entropy fluctuations in specific models.

Abstract

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.