On the coupling of heavy mesons to pions in QCD

We compute the strong coupling constant $g_{P^* P \pi}$, with $P$ and $P^*$ respectively pseudoscalar and vector heavy mesons by using the QCD sum rules approach. Our computation is based on the evaluation of the time ordered product of currents between the vacuum and the soft pion state. The so-called parasitic terms are taken into account and give a contribution to the sum rule of the same order of the lowest lying state, while higher dimension non perturbative terms have small numerical effects. The infinite heavy quark mass limit is also examined.