Abstract
<title>Abstract</title> <p>Every limit on proton decay is reported as a lower bound on the proton lifetimean intrinsic constant of nature. We argue that the proton may possess no such constant. If baryon number is an exact discrete gauge symmetry, locked to the Z3 centre of colour through the embedding of baryon number as a fourth colour, then single-nucleon decay (∆B = 1) and neutronantineutron oscillation (∆B = 2) are forbidden at all scales, including by quantum gravity. The minimal genuinely allowed violation is ∆B = 3, the selection rule the electroweak sphaleron already obeys, and it cannot be carried eciently by any local operator. It is realized instead inside the cores of the Z3 baryonic vortices that the breaking U(1)B →Z3 necessarily produces, via CallanRubakov / AlfordMarch-RussellWilczek catalysis with a strong-interaction cross-section. The observable is then not a lifetime but a rate Γp = ndef σv set by the local density of baryonic defects. We derive this master relation from an explicit SU(4)cB model, prove the anomaly cancellation of the discrete remnant, construct the vortex solution and its core operator, recast existing searches as bounds on a cosmic defect ux, and identify the decisive falsiable signatures that separate this picture from every mass-scale theory of nucleon decay: the permanent absence of all ∆B = 1 modes; a dominant clustered, collinear ∆B = 3 channel; an environment-dependent rate; and a correlation with the ravitational-wave background of a cosmic-string network.</p>