Volume Modulus Inflation and the Gravitino Mass Problem

TL;DR

This paper discusses the constraints on the Hubble constant during inflation in large volume compactification models, proposing a new class where inflation can occur at much higher energy scales than the gravitino mass.

Contribution

It introduces a novel class of models allowing inflation at scales far above the gravitino mass, addressing the traditional H <~ m_{3/2} constraint.

Findings

In large volume models, H <~ m_{3/2}^{3/2} constraint is typical.

Proposes models where inflation occurs far from the present vacuum.

A toy model illustrating the scenario is discussed.

Abstract

The Hubble constant during the last stages of inflation in a broad class of models based on the KKLT mechanism should be smaller than the gravitino mass, H <~ m_{3/2}. We point out that in the models with large volume of compactification the corresponding constraint typically is even stronger, H <~ m_{3/2}^{3/2}, in Planck units. In order to address this problem, we propose a class of models with large volume of compactification where inflation may occur exponentially far away from the present vacuum state. In these models, the Hubble constant during inflation can be many orders of magnitude greater than the gravitino mass. We introduce a toy model describing this scenario, and discuss its strengths and weaknesses.