Chiral symmetry breaking, duality in the $\overline{Q}q$ channel and $b \to \overline{c}cs$ decays

We address the issue of the quark-hadron duality in the spectral densities induced by the heavy-light quark currents anti-Q q. In the limit m_Q ->oo, 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 in these channels is higher than in the vector (pseudoscalar) case. Implications for the nonleptonic decays of B mesons (the b -> anti-c cs transition) are considered.