Coupling the inflaton to an expanding aether

TL;DR

This paper explores a Lorentz-violating inflation model where a scalar inflaton is coupled to an Einstein-aether field, analyzing stability, energy conditions, and inflation dynamics.

Contribution

It introduces a new coupling between the inflaton and aether expansion, detailing conditions for stability and viable inflation within this framework.

Findings

Conditions for stability and positive energy are satisfied.

The inflaton-aether coupling influences slow-roll inflation dynamics.

The model allows for a natural end to inflation despite the coupling.

Abstract

We consider a Lorentz-violating theory of inflation consisting of Einstein-aether theory with a scalar inflaton coupled bilinearly to the expansion of the aether. We determine the conditions for linearized stability, positive energy, and vanishing of preferred-frame post-Newtonian parameters, and find that all these conditions can be met. In homogeneous and isotropic cosmology, the inflaton-aether expansion coupling leads to a driving force on the inflaton that is proportional to the Hubble parameter. This force affects the slow-roll dynamics, but still allows for a natural end to inflation.