How deep can a cosmic void be? Voids-informed theoretical bounds in Galileon gravity

TL;DR

This paper introduces a void-based test for Galileon gravity theories, linking void dynamics to cosmic expansion to set bounds on void depths, thus aiding in assessing model viability.

Contribution

It establishes a new viability condition for Galileon models based on cosmic voids, connecting non-linear void dynamics with the universe's expansion history.

Findings

Approximately 60% of the parameter space is excluded by the new criterion.

Most problematic models fail by redshift z ≲ 10.

Void-based constraints serve as complementary filters for modified gravity models.

Abstract

We establish a void-based consistency test for Galileon scalar-tensor theories. We show that the previously reported unphysical breakdown of the predicted Newtonian force in certain Galileon models is controlled by a single condition linking non-linear void dynamics to the cosmic expansion history. This connection yields a redshift-dependent upper bound on the allowed depth of voids and promotes this requirement to a new viability condition, complementary to standard stability criteria. As an example, we apply this void-based criterion to a linear parameterization in the scale factor constrained by theoretical and observational bounds; we find that $\sim 60\%$ of the parameter space is excluded, with most problematic models failing by $z\lesssim 10$. These results position cosmic voids as sharp, complementary and theory-informed filters for viable modified gravity, enabling more informed priors and parameter-space choices in future cosmological inference.