Massive and modified gravity as self-gravitating media

TL;DR

This paper develops an effective field theory framework for self-gravitating media, unifying descriptions of dark energy and modified gravity through internal symmetries and scalar fields, with implications for large-distance gravitational modifications.

Contribution

It introduces a unified EFT approach for self-gravitating media, linking massive gravity, dark energy, and modified gravity via internal symmetries and scalar fields.

Findings

Massive gravity emerges as a medium propagating in spacetime.

Internal symmetries classify different media like superfluids and solids.

The dark sector can be viewed as a self-gravitating medium with specific thermodynamic properties.

Abstract

We study the effective field theory that describes the low-energy physics of self-gravitating media. The field content consists of four derivatively coupled scalar fields that can be identified with the internal comoving coordinates of the medium. Imposing SO(3) internal spatial invariance, the theory describes supersolids. Stronger symmetry requirements lead to superfluids, solids and perfect fluids, at lowest order in derivatives. In the unitary gauge, massive gravity emerges, being thus the result of a continuous medium propagating in spacetime. Our results can be used to explore systematically the effects and signatures of modifying gravity consistently at large distances. The dark sector is then described as a self-gravitating medium with dynamical and thermodynamic properties dictated by internal symmetries. These results indicate that the divide between dark energy and modified gravity, at large distance scales, is simply a gauge choice.