Cause of Disparity between the Results for the $n\bar{n}$ Transition   Problem
  We show that there is a double counting in the standard model of $n\bar{n}$ mixing in the medium, resulting in full cancellation of leading terms. The direct calculation of $n\bar{n}$ transition, annihilation is performed. For lower limit on the free-space $n\bar{n}$ oscillation time we get $\tau_{min} \sim 10^{31}y$. 
V.I.Nazaruk