Relativistic treatment of light quarks in D and B mesons and W-exchange weak decays

A relativistic bound-state equation is applied to formulate the nonspectator (or W-exchange) decay rates of D, Ds, and B mesons, and their leptonic decay constants. The nonspectator decay rates are also calculated here in the Dirac-equation limit. In this limit we show that up to a logarithm the nonspectator rate grows with heavy-quark mass like m6, faster than the spectator rate of m5. Including an analysis of experimental D, D0, and Ds decay rates shows that the enhancement of D0 decays from the nonspectator diagram is about a quarter of the contribution from the spectator diagram. The relativistically calculated weak decay constant fB is in the 260300-MeV range. Predictions are also made for nonspectator B, Bs, and Bc decay rates &2.. AE