Inflation with Massive Vector Fields

TL;DR

This paper explores how massive vector fields coupled to the inflaton can influence inflationary dynamics, potentially leading to observable non-Gaussianities in the cosmic microwave background.

Contribution

It introduces a model considering all renormalizable couplings with shift symmetry, analyzing the interactions of decomposed vector modes with the inflaton.

Findings

Massive vector fields can naturally couple to the inflaton.

The scalar mode interacts with the inflaton, while the divergence-free vector mode decouples.

The model predicts a level of non-Gaussianity around order one, with some parameter regions showing larger effects.

Abstract

We investigate the coupling between the inflaton and massive vector fields. All renormalizable couplings with shift symmetry of the inflaton are considered. The massive vector can be decomposed into a scalar mode and a divergence-free vector mode. We show that the former naturally interacts with the inflaton and the latter decouples at tree level. The model in general predicts $f_{NL}^\mathrm{equil} = \mathcal{O}(1)$, while in some regions of the parameter space large non-Gaussianity can arise.