Observable neutron–antineutron oscillations in seesaw models of neutrino mass

We show that in a large class of supersymmetric models with spontaneously broken B–L symmetry, neutron–antineutron oscillations occur at an observable level even though the scale of B–L breaking is very high, vB–L∼2×1016 GeV, as suggested by gauge coupling unification and neutrino masses. We illustrate this phenomenon in the context of a recently proposed class of seesaw models that solves the strong CP problem and the SUSY phase problem using parity symmetry. We obtain an upper limit on N–N̄ oscillation time in these models, τN–N̄⩽109–1010 s. This suggests that a modest improvement in the current limit on τN–N̄ of 0.86×108 s will either lead to the discovery of N–N̄ oscillations, or will considerably restrict the allowed parameter space of an interesting class of neutrino mass models.