Precise Determination of {$f_{P_s}/f_P$}} {\bf and Measurement of the ``Perturbative'' Pole Mass from {$f_P$}}

Abstract

We present a compact analytic two-loop expression of the $SU(3{)}_f$ breaking effects on the ratio of the pseudoscalar decay constants $R_P\equiv f_{P_S}/f_P$ ($P\equiv D,B$), from which, we extract the precise values : $R_D=1.15\pm .04$, $R_B=1.16\pm .05$, where the errors are mainly due to the uncalculated ${\alpha }_s^2$-corrections. We also scan carefully the $M_c$ (resp. $M_b$) mass dependence of $f_D$ (resp. $f_B$) in view of precise measurements of the ``perturbative'' c and b pole quark masses from the future data of the decay constants $f_P$.

Comments: {{\bf \bf 9 pages, CERN-TH 7094/93 (published in Phys. Lett. B322 (1994) 247 )