On Power Law Inflation in DBI Models

TL;DR

This paper demonstrates that in string theory-based inflation models with non-canonical kinetic terms, specifically DBI scalar fields, power law inflation can be achieved with a broad class of throat geometries and potentials, extending known results.

Contribution

It shows that power law inflation is not limited to specific throat geometries or potentials but can be realized generally in DBI models with appropriate potentials.

Findings

Power law inflation occurs in DBI models with various throat geometries.

Any throat geometry admits a potential leading to power law inflation.

This generalizes the canonical exponential potential result.

Abstract

Inflationary models in string theory which identify the inflaton with an open string modulus lead to effective field theories with non-canonical kinetic terms: Dirac-Born-Infeld scalar field theories. In the case of a $D$-brane moving in an AdS throat with a quadratic scalar field potential DBI kinetic terms allow a novel realization of power law inflation. This note adresses the question of whether this behaviour is special to this particular choice of throat geometry and potential. The answer is that for any throat geometry one can explicitly find a potential which leads to power law inflation. This generalizes the well known fact that an exponential potential gives power law inflation in the case of canonical kinetic terms.