Massive spin-2 theories

TL;DR

This paper introduces massive spin-2 theories, discusses their non-linear completion challenges, reviews the Boulware-Deser ghost problem, and explores conditions to avoid it, highlighting the non-uniqueness of such theories.

Contribution

It provides an overview of massive spin-2 theories, examines the ghost problem, and identifies conditions under which the ghost can be avoided in truncated theories.

Findings

Boulware-Deser ghost can be avoided with non-Einsteinian derivative structures.

Massive spin-2 theories are not uniquely defined.

Circumventing no-go theorems requires specific derivative structures.

Abstract

We give an introduction to massive spin-2 theories and the problem of their non-linear completion. We review the Boulware-Deser ghost problem and two ways to circumvent classic no-go theorems. In turn, massive spin-2 theories are not uniquely defined. In the case of truncated theories, we show that the Boulware-Deser ghost may only be avoided if the derivative structure of the theory is not tuned to be Einsteinian.