Revisiting fifth forces in the Galileon model

TL;DR

The paper revisits fifth forces in Galileon models and demonstrates that the Vainshtein mechanism can dynamically suppress scalar-mediated forces near massive sources, while the Vainshtein radius $r_\star$ can be tuned over a wide range by adjusting combinations of the five Galileon operators. This parametric freedom decouples laboratory-scale gravitational tests from the far-field scalar coupling, weakening previous constraints. The analysis of the strong coupling scale shows that, inside the Vainshtein region, the effective cutoff is enhanced by background effects, and with all $c_i$ nonzero the strong coupling scale can be made arbitrarily high, extending the EFT’s validity to experimentally inaccessible regimes. Overall, the work suggests a substantially broader allowed parameter space for Galileon theories than previously thought, with implications for their ultraviolet completions and connections to higher-dimensional origins.

Abstract

A Galileon field is one which obeys a spacetime generalization of the non-relativistic Galilean invariance. Such a field may possess non-canonical kinetic terms, but ghost-free theories with a well-defined Cauchy problem exist, constructed using a finite number of relevant operators. The interactions of this scalar with matter are hidden by the Vainshtein effect, causing the Galileon to become weakly coupled near heavy sources. We revisit estimates of the fifth force mediated by a Galileon field, and show that the parameters of the model are less constrained by experiment than previously supposed.