We study the weak-decay constants for the heavy pseudoscalar mesons, D, Ds, B and Bs. For this purpose, we employ the extended nonlocal chiral-quark model (ExNLChQM), motivated by the heavy-quark effective field theory as well as the instanton-vacuum configuration. In addition to the heavy-quark symmetry and the nonlocal interactions between quarks and pseudoscalar mesons in ExNLChQM, a correction for the strange-quark content inside Ds and Bs is also taken into account and found to be crucial to reproduce the empirical values. From those numerical results, we obtain fD, Ds, B, Bs = (207.53, 262.56, 208.13, 262.39) MeV , which are in good agreement with experimental data and other theoretical estimations. Using those numerical results, we estimate the CKM matrix elements and the Cabibbo angle with the various mesonic and leptonic heavy-meson decay channels, resulting in (|Vcd|, |Vcs|, |Vub|, |Vtd|/|Vts|) = (0.224, 0.968, <5.395×10-3, 0.215) and θC = 12.36° which are well compatible with available data.
Heavy-meson decay constants from QCD sum rules