Improved Upper Limits on Baryon-Number Violating Dinucleon Decays to Dileptons

We consider effects of $n-bar n$ oscillations and resultant matter instability due to dinucleons decays. We point out that existing upper bounds on the rates for the dinucleon decays $nn to 2pi^0$, $nn to pi^+pi^-$, and $np to pi^+pi^0$ imply upper bounds on the rates for dinucleon decays to dileptons $nn to e^+ e^-$, $nn to mu^+mu^-$, $nn to u_ell bar u_ell$, and $np to ell^+ u_ell$, where $ell=e, mu, tau$. We present estimates for these upper bounds. Our bounds are substantially stronger than corresponding limits from direct searches.