DBI Inflation and Warped Black Holes

TL;DR

This paper investigates how a sharp feature in the warp factor during DBI inflation can amplify curvature perturbations through a decreasing sound speed, potentially leading to primordial black hole formation.

Contribution

It provides analytical approximations for the dynamics of DBI inflation with a warp feature and explores conditions for primordial black hole production.

Findings

Amplification of curvature perturbations via decreasing sound speed.

Analytical expressions for dynamical quantities during inflation.

Guidelines for constructing models with primordial black hole formation.

Abstract

We study a possible amplification mechanism for the curvature perturbations generated during inflation by a Dirac-Born-Infeld (DBI) inflaton in the presence of a sharp feature in the warp factor. The large growth resulting in the scalar power spectrum is a consequence of the decreasing speed of sound. We obtain analytical approximate expressions for the relevant dynamical quantities both in the slow roll phase and during the transient phase which leads to the amplification. We finally compare our approximations to the exact numerical evolution and give, in such a context, the general rules for building a viable inflationary model leading to, during the subsequent radiation dominated era, an abundant primordial black holes formation.