Explaining the proton radius puzzle with disformal scalars

Brax, Philippe; Burrage, Clare

Abstract

We analyze the consequences of a disformal interaction between a massless scalar and matter particles in the context of atomic physics. We focus on the displacement of the atomic energy levels that it induces, and in particular the change in the Lamb shift between the 2s and 2p states. We find that the correction to the Lamb shift depends on the mass of the fermion orbiting around the nucleus, implying a larger effect for muonic atoms. Taking the cutoff scale describing the effective scalar field theory close to the QCD scale, we find that the disformal interaction can account for the observed difference in the proton radius of muonic versus electronic hydrogen. Explaining the proton radius puzzle is only possible when the scalar field is embedded in nonlinear theories which alleviate constraints from collider and stellar physics. Short distance properties of the Galileon where nonperturbative effects in vacuum are present ensure that unitarity is preserved in high-energy particle collisions. In matter, the chameleon mechanism alleviates the constraints on disformal interactions coming from the burning rates for stellar objects. We show how to combine these two properties in a single model which renders the proposed explanation of the proton radius puzzle viable.

Citation

Brax, P., & Burrage, C. (2015). Explaining the proton radius puzzle with disformal scalars. Physical Review D, D91(4), Article 043515. https://doi.org/10.1103/PhysRevD.91.043515

• Journal Article Type: Article
• Acceptance Date: Feb 11, 2015
• Publication Date: Feb 11, 2015
• Deposit Date: Apr 20, 2017
• Publicly Available Date: Apr 20, 2017
• Journal: Physical Review D
• Print ISSN: 2470-0010
• Electronic ISSN: 2470-0029
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: D91
• Issue: 4
• Article Number: 043515
• DOI: https://doi.org/10.1103/PhysRevD.91.043515
• Public URL: https://nottingham-repository.worktribe.com/output/745097
• Publisher URL: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.91.043515
• Contract Date: Apr 20, 2017