Bimetric Starobinsky model

TL;DR

This paper explores a bimetric extension of the Starobinsky inflation model, demonstrating that inflationary predictions remain consistent and viable dark matter scenarios persist within this generalized framework.

Contribution

It introduces a bimetric version of the Starobinsky model, maintaining inflationary behavior and dark matter interpretation while satisfying bimetric consistency conditions.

Findings

Inflationary behavior remains intact in the bimetric generalization.

The model preserves the interpretation of the massive spin-2 particle as dark matter.

All bimetric consistency requirements are satisfied in the generalized model.

Abstract

The bimetric theory of gravity is an extension of general relativity that describes a massive spin-$2$ particle in addition to the standard massless graviton. The theory is based on two dynamical metric tensors with their interactions constrained by requiring the absence of the so-called Boulware-Deser ghost. It has been realized that the quantum interactions of matter fields with gravity are bound to generate modifications to the standard Einstein-Hilbert action such as quadratic curvature terms. Such a quadratic Ricci scalar term is present in the so-called Starobinsky model which has been proven to be rather robust in its inflationary predictions. In the present article we study a generalization of the Starobinsky model within the bimetric theory and find that its inflationary behavior stays intact while keeping all consistency requirements of the bimetric framework. The interpretation of the massive spin-2 particle as dark matter remains a viable scenario, as in standard bigravity.