Beyond Amplitudes' Positivity and the Fate of Massive Gravity

TL;DR

This paper extends positivity bounds to constrain effective field theories like Galileon and massive gravity, showing that experimental and theoretical limits challenge their viability in describing gravitational phenomena.

Contribution

It introduces new bounds beyond traditional positivity constraints, impacting the viability of massive gravity and Galileon theories in explaining gravity.

Findings

Massive gravity is either ruled out or incompatible with fifth-force tests.

Galileon theories require symmetry-breaking terms at most one-loop suppressed.

Theoretical bounds restrict the parameter space of these models.

Abstract

We constrain effective field theories by going beyond the familiar positivity bounds that follow from unitarity, analyticity, and crossing symmetry of the scattering amplitudes. As interesting examples, we discuss the implications of the bounds for the Galileon and ghost-free massive gravity. The combination of our theoretical bounds with the experimental constraints on the graviton mass implies that the latter is either ruled out or unable to describe gravitational phenomena, let alone to consistently implement the Vainshtein mechanism, down to the relevant scales of fifth-force experiments, where general relativity has been successfully tested. We also show that the Galileon theory must contain symmetry-breaking terms that are at most one-loop suppressed compared to the symmetry-preserving ones. We comment as well on other interesting applications of our bounds.