Prediction — rₚ BCT Letter 12: The Proton Charge Radius from BCT Void Geometry — Resolving the Proton Radius Puzzle

The proton charge radius has been the subject of intense debate since 2010, when muonic hydrogen spectroscopy yielded rp = 0.8409±0.0004 fm—4% smaller than the then-accepted CODATA value of 0.8768 ± 0.0069 fm from electronic measurements. This "proton radius puzzle" prompted extensive experimental and theoretical work. The current CODATA 2018 recommended value is rp = 0.8414± 0.0019 fm, converging toward the muonic result. We derive the proton charge radius from the void geometry of the Body-Centred Tetragonal (BCT) vacuum lattice with zero free parameters: rp = (√ 12/mρ)(1 + κpα0) = 0.8386 fm, where κp = roct/rtet × (1 − α0) = 1.829 is the BCT proton anomalous magnetic moment and α0 = 0.0074081 is the crystal coupling. The error is −0.33% from the CODATA value. BCT naturally produces the smaller radius consistent with muonic hydrogen, supporting the resolution of the proton radius puzzle in favour of the muonic measurement. The derivation chain ΛQCD → fπ → mρ + κp → rp contains no fitted hadronic parameters.