Relativistic treatment of light quarks inDandBmesons andW-exchange weak decays

A relativistic bound-state equation is applied to formulate the nonspectator (or W-exchange) decay rates of D, $D_s$, 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 $m^6$, faster than the spectator rate of $m^5$. Including an analysis of experimental $D^{\pm }$, $D^0$, and $D_s$ decay rates shows that the enhancement of $D^0$ decays from the nonspectator diagram is about a quarter of the contribution from the spectator diagram. The relativistically calculated weak decay constant $f_B$ is in the 260–300-MeV range. Predictions are also made for nonspectator B, $B_s$, and $B_c$ decay rates &≃2. .AE