A particle's perspective on screening mechanisms

TL;DR

This paper investigates the theoretical foundations of screening mechanisms in scalar-tensor theories, especially Brans-Dicke models, highlighting the role of the Standard Model and scale symmetries in modulating fifth forces and gravitational constants.

Contribution

It provides a field theory perspective on screening mechanisms, emphasizing the influence of the Standard Model and Higgs mechanism on their effectiveness in scalar-tensor theories.

Findings

Screening mechanisms depend on sectors obtaining mass via the Higgs mechanism.

Certain regions of parameter space exhibit spatially varying gravitational constants.

Over-screening can occur when screening effects surpass fifth force suppression.

Abstract

Screening mechanisms are a natural method for suppressing long-range forces in scalar-tensor theories as they link the local background density to their strength. Focusing on Brans-Dicke theories, those including a non-minimal coupling between a scalar degree of freedom and the Ricci scalar, we study the origin of these screening mechanisms from a field theory perspective, considering the influence of the Standard Model on the mechanisms. Additionally, we further consider the role of scale symmetries on screening, demonstrating that only certain sectors, those obtaining their mass via the Higgs mechanism, contribute to screening the fifth forces. This has significant implications for baryons, which obtain most of their mass from the gluon's binding energy. Given that the Planck mass is related to the vacuum expectation value of the non-minimally coupled field, we find an extensive region of the parameter space where screening mechanisms create a spatially dependent gravitational constant. We say that the field over-screens when this effect is more significant than the fifth forces suppressed by screening mechanisms, as we illustrate for the chameleon and symmetron models.