Hide and Seek: Screened Scalar Fields in Hydrogen and Muonium

TL;DR

This paper investigates how screened scalar fields affect hydrogen-like systems, revealing that muonium experiments can provide sensitive tests for these theories, especially in parameter regions not constrained by previous low-energy experiments.

Contribution

The study computes energy level perturbations caused by screened scalar fields and demonstrates that muonium experiments are highly sensitive probes for these fields, surpassing previous bounds.

Findings

Hydrogen spectroscopy yields weaker bounds when screening is considered.

Muonium experiments are more sensitive to screened scalar fields.

Significant unexplored parameter space remains for chameleon models.

Abstract

We compute bounds on screened scalar field theories from hydrogen-like systems. New light scalar fields generically have a direct coupling to matter. Such a coupling is strongly constrained by myriad experimental measurements. However, certain theories possess a {\it screening mechanism} that allows the effects of this coupling to weaken dynamically, and to evade many such bounds. We compute the perturbations to the energy levels of hydrogen-like systems due to screened scalar fields. We then use this result in two ways. First, we compute bounds from hydrogen spectroscopy, finding significantly weaker bounds than have been reported before as screening effects were overlooked. Second, we show that muonium is an intrinsically much more sensitive probe of screened scalar fields. For chameleon models, muonium experiments probe a large part of the parameter space that is as yet unexplored by low energy physics and has so far only been tested by high-energy particle physics experiments.