A quark loop model for heavy mesons

I consider a model based on a quark–meson interaction Lagrangian. The transition amplitudes are evaluated by computing diagrams in which heavy and light mesons are attached to quark loops. The light chiral symmetry relations and the heavy quark spin-flavour symmetry dictated by the heavy quark effective theory are implemented. The model allows to compute the decay form factors and therefore can give predictions for the decay rates, the invariant mass spectra and the asymmetries. INTRODUCTION The increasing number of available data on heavy meson processes demands theoretical predictions for these processes to be compared with experiment. I consider a simple model, based on an effective constituent quark-meson Lagrangian containing both light and heavy degrees of freedom, constrained by the known symmetries of QCD in the limit mQ → ∞ and the light chiral symmetry relations. I write a Lagrangian at the mesonquark level [1]. This allows to deduce from a small number of parameters the heavy meson couplings and form factors, with a considerable reduction in the number of free parameters with respect to the Lagrangian written in terms of meson fields only [2]. The part of the quark-meson effective Lagrangian involving heavy and light quarks and heavy mesons is: