Extracting infrared QCD coupling from meson spectrum

. In the framework of the Bethe-Salpeter formalism used in previous papers to evaluate the quarkonium spectrum, here we reverse the point of view to extract an “experimental” running coupling a exps ( Q 2 ) in the infrared (IR) region from the data. The values so obtained agree within the erros with the Shirkov-Solovtsov analytic coupling for 200 MeV < Q < 1.2 GeV, thus giving a very satisfactory unifying description of high and low energy phenomena. Below 1 GeV however a exps ( Q 2 ) seems to vanish as Q → 0. The paper is based on a work in progress in collaboration with D. V. Shirkov.