The quark axial vector coupling and heavy meson decays

Form factors and decay widths for D∗ → Dγ and D∗ → Dπ decays are estimated in a relativistic constituent quark model. Relativistic corrections due to light quarks are found to be substantial and to suppress the vector and axial vector form factors. The CLEO experimental value of Dγ0 ≡ Γ(D∗0 → D0γ)Γ(D∗0 → D0π0) = 0.572 ± 0.057 ± 0.081 is used to determine the quark axial vector coupling gA, which is found to be 0.6-0.8 for mu = (350-200) MeV correspondingly, as compared with the chiral model result gA = 0.8−0.9. The heavy meson-pion strong coupling g is found to be 0.4-0.6, much smaller than g = 1 which is expected in the large NC and nonrelativistic limit, but consistent with some heavy hadron chiral theory and QCD sum rule results.