Reducing model dependence of spectator effects in inclusive decays of heavy baryons

The dependence of the inclusive weak decay rates of heavy hadrons on light spectator quarks is considered. The analysis of a previous work relating the effects in b baryons to those in charmed baryons is extended to explicit evaluation of the matrix elements of certain four-quark operators over heavy baryons. It is shown that the usually postulated color antisymmetry of these matrix elements is significantly broken. The flavor-singlet shift of the inclusive decay rates of b baryons due to spectator effects is shown to be strongly suppressed in the leading-logarithmic approximation. Combined with the results for the flavor-nonsinglet splittings, this observation allows us to argue, in a less model-dependent way than before, that within the present understanding of spectator effects it is highly unlikely that the lifetimes of the ${\Lambda }_b$ and the $B_d$ can be split by more than 10%.