Decay Constants of Heavy-Light Mesons from QCD

We summarize our recently improved results for the pseudoscalar [1, 2], vector and B-c [3] meson decay constants from QCD spectral sum rules where N2LO circle plus estimate of the N3LO PT circle plus d <= 6 condensates have been included in the SVZ expansion. The "optimal results" based on stability criteria with respect to the variations of the Laplace/Moments sum rule variables, QCD continuum threshold and subtraction constant mu are compared with recent sum rules and lattice calculations. To understand the "apparent tension" between some recent results, we present in Section 8 a novel extraction of for f(B*)/f(B) from heavy quark effective theory (HQET) sum rules by including the normalization factor (M-b/M-B)(2) relating the pseudoscalar to the universal HQET correlators for finite b-quark and B-meson masses. We obtain f(B*)/f(B) = 1.025(16) in good agreement with 1.016(16) from spectral sum rules (SR) in full QCD [3]. We complete the paper by including new improved estimates of the scalar, axial and B-c* meson decay constants (Sections 11-13). For further phenomenological uses, we attempt to extract a Global Average of the sum rules and lattice determinations which are summarized in Tables 2-6. We do not found any deviation of these SM results from the present data.