Volume Stabilization and the Origin of the Inflaton Shift Symmetry in String Theory

TL;DR

This paper identifies a class of string theory inflation models where a shift symmetry naturally arises from the mathematical structure of the theory, aiding in volume stabilization and potential flatness.

Contribution

It demonstrates how the shift symmetry in certain string models originates from the coset space symmetry and special geometry, linking mathematical structure to inflationary potential.

Findings

Shift symmetry linked to coset space properties.

Type IIB on K3xT^2/Z exhibits specific symmetry groups.

Absence of prepotential influences the construction.

Abstract

The main problem of inflation in string theory is finding the models with a flat potential, consistent with stabilization of the volume of the compactified space. This can be achieved in the theories where the potential has (an approximate) shift symmetry in the inflaton direction. We will identify a class of models where the shift symmetry uniquely follows from the underlying mathematical structure of the theory. It is related to the symmetry properties of the corresponding coset space and the period matrix of special geometry, which shows how the gauge coupling depends on the volume and the position of the branes. In particular, for type IIB string theory on K3xT^2/Z with D3 or D7 moduli belonging to vector multiplets, the shift symmetry is a part of SO(2,2+n) symmetry of the coset space [SU(1,1)/ U(1)]x[SO(2,2+n)/(SO(2)x SO(2+n)]. The absence of a prepotential, specific for the stringy version of supergravity, plays a prominent role in this construction, which may provide a viable mechanism for the accelerated expansion and inflation in the early universe.