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

The dependence of inclusive weak decay rates of heavy hadrons on light spectator quarks is considered. The analysis of a previous work on 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 inclusive decay rates of b baryons due to the spectator effects is shown to be strongly suppressed in the leading-log approximation. Combined with the results for the flavor non-singlet splittings, this observation allows to argue, in a less model-dependent way, than before, that within the present understanding of the spectator effects it is highly unlikely that the lifetimes of the Lambda_b and the B_d can be split by more than 10%.