Chiral symmetry breaking, duality in the overlineQq channel and b → overlinecs decays

We address the issue of the quark-hadron duality in the spectral densities induced by the heavy-light quark currents overlineQq . In the limit m_Q → ∞, m_q → 0 we observe an enhancement of the physical spectral density compared to the quark one in the scalar and axial channels, due to the Goldstone meson contributions. This may imply that the scale where duality sets in is higher in these channels than in the vector (pseudoscalar) case. Implications for the non-leptonic decays of B mesons (the b → overlineccs transition) are considered. We discuss in detail the decay pattern and obtain an independent estimate of the "wrong"-sign D yield.