Spectator Effects in Inclusive Decays of Beauty Hadrons
  We evaluate the matrix elements of the four-quark operators which contribute to the lifetimes of $B$-mesons and the $\Lambda_b$-baryon. We find that the spectator effects are not responsible for the discrepancy between the theoretical prediction and experimental measurement of the ratio of lifetimes $\tau(\Lambda_b)/\tau(B)$. 
Massimo Di Pierro and Chris T. Sachrajda