Scalar instabilities in bimetric gravity: The Vainshtein mechanism and structure formation

TL;DR

This paper examines how scalar instabilities in bimetric gravity influence cosmic structure formation, focusing on the Vainshtein mechanism's role in restoring general relativity and constraining the instability onset redshift.

Contribution

It provides observational constraints on scalar instabilities in bimetric gravity, especially the redshift below which these instabilities are suppressed, for the minimal beta_1-model.

Findings

Early time instabilities have negligible impact on observed structures.

Constraints suggest instabilities are ruled out below redshift z_i ≈ 0.5.

Potential to test or rule out the minimal beta_1-model with future data.

Abstract

We investigate the observational consequences of scalar instabilities in bimetric theory, under the assumption that the Vainshtein mechanism restores general relativity within a certain distance from gravitational sources. We argue that early time instabilities have a negligible impact on observed structures. Assuming that the instabilities affect sub-horizon density fluctuations, we constrain the redshift, z_i, below which instabilities are ruled out. For the "minimal" beta_1-model, observational constraints are close to the theoretical expectations of z_i = 0.5, potentially allowing the model to be ruled in or out with a more detailed study, possibly including secondary cosmic microwave background constraints.