Robustness of kinetic screening against matter coupling

TL;DR

This paper examines the robustness of kinetic screening mechanisms in scalar-tensor gravity theories with matter couplings, finding that kinetic screening generally dominates over scalarization and can be modulated by kinetic couplings, with potential astrophysical implications.

Contribution

It demonstrates that kinetic screening remains effective against matter couplings and introduces a method to weaken screening via fine-tuning kinetic couplings, revealing new testable signatures.

Findings

Kinetic screening dominates over scalarization in neutron stars.

Kinetic matter couplings enhance scalar gradient suppression.

Fine-tuning kinetic couplings can weaken screening effects.

Abstract

We investigate neutron star solutions in scalar-tensor theories of gravity with first-order derivative self-interactions in the action and in the matter coupling. We assess the robustness of the kinetic screening mechanism present in these theories against general conformal couplings to matter. The latter include ones leading to the classical Damour-Esposito-Far\`ese scalarization, as well as ones depending on the kinetic term of the scalar field. We find that kinetic screening always prevails over scalarization, and that kinetic couplings with matter enhance the suppression of scalar gradients inside the star even more, without relying on the non-linear regime. Fine tuning the kinetic coupling with the derivative self-interactions in the action allows one to partially cancel the latter, resulting in a weakening of kinetic screening inside the star. This effect represents a novel way to break screening mechanisms inside matter sources, and provides new signatures that might be testable with astrophysical observations.