DECAY CONSTANTS AND MIXING PARAMETERS IN A RELATIVISTIC MODEL FOR A Q(Q)OVER-BAR SYSTEM

We extend our recent work, in which the Dirac equation with a ''(asymp totically free) Coulomb + (Lorentz scalar gamma(0) sigma r) linear'' p otential is used to obtain the light quark wave function for q (Q) ove r bar mesons in the limit m(Q)-->infinity to estimate the decay consta nt f(P) and the mixing parameter B of the pseudoscalar mesons. We comp are our results for the evolution of f(P) and B with the meson mass M( P), to the nonrelativistic formulas for these quantities and show that there is a significant correction in the subasymptotic region. For si gma=0.14 GeV-2 and Lambda(<(MS)over bar>)=0.240 GeV we obtain f(D)=0.3 71, f(DS)=0.442, f(B)=0.301, f(Bs)=0.368 GeV, and B-D=0.88, B-Ds=0.89, B-B=0.95, B-Bs=0.96, and B-K=0.60.