Fluctuations along supersymmetric flat directions during Inflation

TL;DR

This paper investigates how scalar field fluctuations during inflation are affected by gauge and Yukawa couplings, revealing that non-flat directions can suppress fluctuations along flat directions, challenging previous assumptions.

Contribution

It provides a numerical analysis of field fluctuations during inflation in supersymmetric models, showing the impact of gauge and Yukawa couplings on flat direction fluctuations.

Findings

Fluctuations along non-flat directions can suppress flat direction fluctuations.

The usual linear growth of <φ^2> with e-folds can be violated.

Results suggest revising cosmological models assuming free flat direction fluctuations.

Abstract

We consider a set of scalar fields, consisting of a single flat direction and one or several non-flat directions. We take our cue from the MSSM, considering separately D-flat and F-flat directions, but our results apply to any supersymmetric scenario containing flat directions. We study the field fluctuations during pure de Sitter Inflation, following the evolution of the infrared modes by numerically solving the appropriate Langevin equations. We demonstrate that for the Standard Model U(1), SU(2) or SU(3) gauge couplings, as well as for large enough Yukawa couplings, the fluctuations along the non-flat directions effectively block the fluctuations along the flat directions. The usual expected behaviour <{\phi}^2> \propto N, with N the number of efolds, may be strongly violated, depending on the coupling strengths. As a consequence, those cosmological considerations, which are derived assuming that during inflation flat directions fluctuate freely, should be revised.