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. 
Bhaskar Dutta, Yukihiro Mimura and R. N. Mohapatra