Chiral symmetry breaking, duality in the (Q)over-bar-q channel and b->(c)over-bar-cs decays

We address the issue of the quark-hadron duality in the spectral densities induced by the heavy-light quark currents (Q) over bar q. In the limit m(Q) --> infinity, 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 --> (c) over bar cs transition) are considered. We discuss in detail the decay pattern and obtain an independent estimate of the ''wrong''-sign D yield. (C) 1997 Elsevier Science B.V.