Constraints on Shift-Symmetric Scalar-Tensor Theories with a Vainshtein Mechanism from Bounds on the Time Variation of G

TL;DR

Current observational bounds on the variation of Newton's constant G impose strong constraints on shift-symmetric scalar-tensor theories with Vainshtein screening, especially those with significant matter-scalar coupling, affecting their viability.

Contribution

This paper demonstrates that local bounds on G's variation severely restrict certain scalar-tensor theories with screening mechanisms, highlighting limitations of the Vainshtein mechanism in these models.

Findings

Local bounds on G variation constrain scalar-tensor theories.

Vainshtein screening cannot fully hide scalar effects in some models.

Large matter-scalar coupling leads to incompatible G variation.

Abstract

We show that the current bounds on the time variation of the Newton constant G can put severe constraints on many interesting scalar-tensor theories which possess a shift symmetry and a nonminimal matter-scalar coupling. This includes, in particular, Galileon-like models with a Vainshtein screening mechanism. We underline that this mechanism, if efficient to hide the effects of the scalar field at short distance and in the static approximation, can in general not alter the cosmological time evolution of the scalar field. This results in a locally measured time variation of G which is too large when the matter-scalar coupling is of order one.