Sub-GeV U(1)(R ) gauge boson to address the proton radius discrepancy

We propose a Standard Model extension by a U(1)(R) gauge symmetry where only right-handed chiral fermions can carry a nontrivial charge. Here, we show that the simplest anomaly-free solution to accommodate the proton charge radius discrepancy takes right-handed muons, mu(R), and first generation quarks, u(R) and d(R). Consistency with the latest muon's (g - 2) measurements is achieved through an extra light scalar, which itself must lie in the tens of MeV mass range to be viable.