Nonlinear interactions for massive spin-2 fields

TL;DR

This paper introduces ghost-free nonlinear theories for massive spin-2 fields, focusing on bimetric theory, its structure, solutions, and applications to cosmology, highlighting the connection to general relativity.

Contribution

It provides a comprehensive review of ghost-free nonlinear massive spin-2 theories, especially bimetric theory, including its solutions, spectrum, and cosmological relevance.

Findings

Bimetric theory admits maximally symmetric solutions.

The mass spectrum of bimetric theory is characterized.

The theory approaches general relativity in a specific parameter limit.

Abstract

We give a basic introduction to ghost-free nonlinear theories involving massive spin-2 fields, focussing on bimetric theory. After motivating the construction of such models from field theoretical considerations, we review the linear theories for massive and massless spin-2 fluctuations propagating on maximally symmetric backgrounds. The structure of general nonlinear spin-2 interactions is explained before we specialise to the ghost-free case. We review the maximally symmetric solutions of bimetric theory, its mass spectrum and the parameter limit which brings the theory close to general relativity. Finally we discuss applications of bimetric theory to cosmology with particular emphasis on the role of the general relativity limit.