Effects of Light Fields During Inflation

TL;DR

This paper investigates how light fields during inflation can generate primordial perturbations, providing criteria to distinguish their significance, with applications to D-brane inflation models and effects from extra modes.

Contribution

It introduces criteria to determine when light fields influence inflationary perturbations and applies these to specific string-inspired inflation models.

Findings

Light fields can source significant curvature perturbations during inflation.

Criteria are established to identify impactful light fields in multi-field scenarios.

Applications to D-brane inflation models demonstrate the relevance of extra modes.

Abstract

In the inflationary universe, there can be light fields other than the inflaton. We explore a possibility that such light fields source the primordial perturbations, while minimally affecting the inflaton dynamics. We show that during inflation, fluctuations of the light fields can be converted to adiabatic curvature perturbations, which accumulate and become significant by the end of the inflationary era. An additional goal of this work is to distinguish between light fields which can/cannot be ignored during inflation. Such criteria become useful for examining cosmological scenarios with multiple fields. As concrete examples, our results are applied to D-brane inflation models. We consider effects from KK modes (oscillation modes) of wrapped branes in monodromy-driven large-field models, and angular directions of throat geometries in warped D-brane inflation.