Compact Exotic Tetraquark Mesons in Large-N_c QCD

¹ Institute for High Energy Physics, Austrian Academy of Sciences, Nikolsdorfergasse 18, A-1050 Vienna, Austria
² D. V. Skobeltsyn Institute of Nuclear Physics, M. V. Lomonosov Moscow State University, 119991, Moscow, Russia
³ Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria
⁴ Institut de Physique Nucléaire, CNRS-IN2P3, Université Paris-Sud, Université Paris-Saclay, 91406 Orsay Cedex, France

^* e-mail: Wolfgang.Lucha@oeaw.ac.at
^** e-mail: dmitri_melikhov@gmx.de
^*** e-mail: sazdjian@ipno.in2p3.fr

Published online: 31 October 2018

Abstract

We embark on systematic explorations of the behaviour of tetraquark mesons, i.e., colour-singlet bound states of two quarks and two antiquarks, in the (idealized) limit of a large number of colour degrees of freedom, N_c,; of quantum chromodynamics, QCD. Considering the scattering of two ordinary mesons into two ordinary mesons, we start off with formulating a set of selection criteria that should enable us to unambiguously single out precisely those contributions to all encountered scattering amplitudes that potentially will develop tetraquark poles. Assuming that tetraquark mesons do exist and, if so, emerge in the contributions compatible with our criteria at largest admissible order of N_c; we deduce, for the categories of tetraquarks that exhibit either four or only two different open quark flavours, that the decay rates of these tetraquark types are, at least, of order 1/N²_c and that internal consistency requires all the members of the first species to exist pairwise, distinguishable by their favoured two-ordinary-meson decay channels.