Microscopic study of the string breaking in QCD

Theory of strong decays defines in addition to decay widths also the channel coupling and the mass shifts of the levels above the decay thresholds. In the standard decay models of the (3) P (0) type the decay vertex is taken to be a phenomenological constant gamma and such a choice leads to large mass shifts of all meson levels due to real and virtual decays, the latter giving a divergent contribution. Here we show that taking the microscopic details of decay vertex into account, one obtains new string width effect coefficient, which strongly suppresses virtual decay contribution. In addition for a realistic space structure of the decay vertex of highly excited states, the decay matrix elements appear to be strongly different from those, where the constant gamma is used. From our analysis also follows that so-called flattening potential can imitate the effects of intermediate decay channels.