Observable Neutron Antineutron Oscillation in High Scale Seesaw Models

We discuss a realistic high scale ($v_{BL}\sim 10^{12}$ GeV) supersymmetric seesaw model based on the gauge group $SU(2)_L\times SU(2)_R\times SU(4)_c$ where neutron-anti-neutron oscillation can occur at an observable rate. This is contrary to the naive dimensional arguments which say that $\tau_{N-\bar{N}}\propto v_{BL}^5$ and is therefore unobservable if the seesaw scale $v_{BL}\geq 10^{5}$ GeV. Two reasons for the enhanced rate in our model are: (i) accidental global symmetries which keep some of the diquark Higgs masses at the weak scale and (ii) a new supersymmetric contribution from a lower dimensional operator. The net result is that $\tau_{N-\bar{N}}\propto v_{BL}^2 v^3_{wk}$ rather than $v^5_{BL}$, causing the enhancement. The model can also explain the origin of matter via leptogenesis and is testable at LHC where the light diquark states can be produced.