Nonmesonic weak decay of $\Lambda$ hypernuclei within a nuclear matter   framework
  The nonmesonic weak decay of $\Lambda$ hypernuclei is studied using nuclear matter. We have developed a formalism which gives a microscopic interpretation of the process of emission of particles originated in this decay. More specifically, our scheme provides a unified treatment of $\Gamma(\Lambda N \to NN$) and $N_{N}$ ($N_{NN}$), the $\Lambda$ non-mesonic weak decay widths and the number of emitted particles (pair of particles) of kind $N$ ($NN$), respectively. We have also evaluated for the first time the quantum interference terms between the $n$- and $p$-induced weak decay amplitudes. Explicit expressions for $N_{N}$ and $N_{NN}$ are shown within the ring approximation. Using the local density approximation together with the ring approximation, we report results for the decay of the $^{12}_{\Lambda}C$ hypernucleus. We have obtained values for the ratio $N_{n}/N_{p}$ ($N_{nn}/N_{np}$) in the range $1.4-1.6$ ($0.2-0.3$), where no energy threshold have been employed. The $n$- and $p$-induced interference terms modify in less than $\sim 3 %$ these results. 
E. Bauer