We show that off-mass-shell effects arising from the internal structure of
the proton provide a new proton polarization mechanism in the Lamb shift,
proportional to the lepton mass to the fourth power. This effect is capable of
resolving the current puzzle regarding the difference in the proton radius
extracted from muonic compared with electronic hydrogen. These off-mass-shell
effects could be probed in several other experiments.Comment: 6 pages, 1 figure. This revised version contains various
clarification
