Screening the fifth force in the Horndeski's most general scalar-tensor theories

TL;DR

This paper investigates how the Vainshtein screening mechanism operates in the most general scalar-tensor theories with second-order equations, clarifying conditions for fifth force suppression in various models.

Contribution

It derives general field equations for screening in scalar-tensor theories and applies them to specific models like Galileons, elucidating conditions for effective fifth force suppression.

Findings

Vainshtein mechanism can suppress fifth force in various models.

Conditions for screening depend on the dominance of kinetic terms.

Solutions connect interior and exterior fields in spherically symmetric bodies.

Abstract

We study how the Vainshtein mechanism operates in the most general scalar-tensor theories with second-order equations of motion. The field equations of motion, which can be also applicable to most of other screening scenarios proposed in literature, are generally derived in a spherically symmetric space-time with a matter source. In the presence of a field coupling to the Ricci scalar, we clarify conditions under which the Vainshtein mechanism is at work in a weak gravitational background. We also obtain the solutions of the field equation inside a spherically symmetric body and show how they can be connected to exterior solutions that accommodate the Vainshtein mechanism. We apply our general results to a number of concrete models such as the covariant/extended Galileons and the DBI Galileons with Gauss-Bonnet and other terms. In these models the fifth force can be suppressed to be compatible with solar-system constraints, provided that non-linear field kinetic terms coupled to the Einstein tensor do not dominate over other non-linear field self-interactions.