| Abstract: | In 2010 the proton charge radius was extracted for the first time from
muonic hydrogen, a bound state of a muon and a proton. The value
obtained was five standard deviations away from the regular hydrogen
extraction. Taken at face value, this might be an indication of a new
force in nature coupling to muons, but not to electrons. It also forces
us to reexamine our understanding of the structure of the proton.
This "proton radius puzzle" can be viewed as the latest chapter in a
100+ year old adventure: how hydrogen spectroscopy keeps pushing the
boundaries of science. I will briefly review this history and describe
an ongoing theoretical research effort to address this puzzle. In
particular, I will present a reevaluation of the proton structure
effects, correcting 40 years of such calculations, and the development
of new effective field theory tools. |
