Hide and Seek: Screened Scalar Fields in Hydrogen and Muonium

Understand

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.