Modified Gravity via Spontaneous Symmetry Breaking

TL;DR

This paper develops effective field theories where gravity is altered through spontaneous Lorentz symmetry breaking, leading to additional graviton modes and potential large-scale cosmological effects, while remaining consistent with known gravity tests.

Contribution

It introduces a gravitational Higgs-like mechanism with spontaneous Lorentz symmetry breaking, resulting in modified gravity theories free of discontinuities and compatible with experiments.

Findings

Presence of multiple graviton modes with positive norm

Absence of van Dam-Veltman-Zakharov discontinuity

Potential implications for large-scale cosmology

Abstract

We construct effective field theories in which gravity is modified via spontaneous breaking of local Lorentz invariance. This is a gravitational analogue of the Higgs mechanism. These theories possess additional graviton modes and modified dispersion relations. They are manifestly well-behaved in the UV and free of discontinuities of the van Dam-Veltman-Zakharov type, ensuring compatibility with standard tests of gravity. They may have important phenomenological effects on large distance scales, offering an alternative to dark energy. For the case in which the symmetry is broken by a vector field with the wrong sign mass term, we identify four massless graviton modes (all with positive-definite norm for a suitable choice of a parameter) and show the absence of the discontinuity.