Spontaneous Lorentz Breaking and Massive Gravity

TL;DR

This paper explores a theory where an extra spin-two field causes spontaneous Lorentz symmetry breaking, resulting in massive gravity with unique gravitational wave behavior and potential observable effects.

Contribution

It introduces a model with spontaneous Lorentz breaking that yields massive gravity, preserving the Weak Equivalence Principle and predicting distinctive gravitational wave phenomena.

Findings

Gravity becomes massive in the broken phase.

Gravitational waves include both massless and massive components.

Potential observable differences in graviton and photon arrival times.

Abstract

We study a theory where the presence of an extra spin-two field coupled to gravity gives rise to a phase with spontaneously broken Lorentz symmetry. In this phase gravity is massive, and the Weak Equivalence Principle is respected. The newtonian potentials are in general modified, but we identify an non-perturbative symmetry that protects them. The gravitational waves sector has a rich phenomenology: sources emit a combination of massless and massive gravitons that propagate with distinct velocities and also oscillate. Since their velocities differ from the speed of light, the time of flight difference between gravitons and photons from a common source could be measured.