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Дата последнего поиска статьи во внешних источниках: 26 марта 2018 г.
Аннотация:Considering four-point correlation functions of color-singlet quark bilinears, we investigate, in the large-Nc limit of QCD, the subleading diagrams that involve, in the s-channel of meson–meson scattering amplitudes, two-quark–two-antiquark intermediate states. The latter contribute, together with gluon exchanges, to the formation, at the hadronic level, of two-meson and tetraquark intermediate states. It is shown that the two-meson contributions, which are predictable, in general, from leading-order Nc-behaviors, consistently satisfy the constraints resulting from the 1/Nc expansion procedure and thus provide a firm basis for the extraction of tetraquark properties from Nc-subleading diagrams. We find that, in general, tetraquarks, if they exist in compact form, should have narrow decay widths, of the order of Nc^{-2}. For the particular case of exotic tetraquarks, involving four different quark flavors, two different types of tetraquark are needed, each having a preferred decay channel, to satisfy the consistency constraints.