Brane-Antibrane Inflation in Orbifold and Orientifold Models

TL;DR

This paper explores how brane-antibrane systems in string theory can naturally lead to cosmic inflation, with the radion or dilaton acting as the inflaton, and discusses mechanisms for ending inflation and reheating.

Contribution

It demonstrates that in realistic orbifold and orientifold models, brane-antibrane attraction induces inflation with favorable slow-roll conditions and links inflationary parameters to the string scale.

Findings

Inflation driven by radion or dilaton fields in brane-antibrane systems.

Conditions for slow-roll inflation are more generic with fixed branes.

Relations established between inflation parameters and the string scale.

Abstract

We analyse the cosmological implications of brane-antibrane systems in string-theoretic orbifold and orientifold models. In a class of realistic models, consistency conditions require branes and antibranes to be stuck at different fixed points, and so their mutual attraction generates a potential for one of the radii of the underlying torus or the 4D string dilaton. Assuming that all other moduli have been fixed by string effects, we find that this potential leads naturally to a period of cosmic inflation with the radion or dilaton field as the inflaton. The slow-roll conditions are satisfied more generically than if the branes were free to move within the space. The appearance of tachyon fields at certain points in moduli space indicates the onset of phase transitions to different non-BPS brane systems, providing ways of ending inflation and reheating the corresponding observable brane universe. In each case we find relations between the inflationary parameters and the string scale to get the correct spectrum of density perturbations. In some examples the small numbers required as inputs are no smaller than 0.01, and are the same small quantities which are required to explain the gauge hierarchy.