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, Nc,; 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 Nc; 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/N2c and that internal consistency requires all the members of the first species to exist pairwise, distinguishable by their favoured two-ordinary-meson decay channels.
Highlights
For obvious reasons, with the mesonic and simpler case of tetraquarks, we approach this issue by investigating the manifestation of tetraquark mesons as intermediate states in scattering reactions of two ordinary mesons into two ordinary mesons in form of contributions of poles to the associated scattering amplitudes [1,2,3,4,5,6]
We tackle this task in two steps: First, we attempt to formulate rigorous criteria that allow us to isolate the contributions of Feynman diagrams capable of developing a pole interpretable as being related to a compact tetraquark meson; we shall refer to the members of this class of Feynman diagrams potentially of interest to us as the tetraquark-friendly, or tetraquark-phile, ones
In order to establish the contribution of a tetraquark T of mass mT viewed as bound state of four quarks (q)i of masses mi, i = 1, . . . , 4, to the s channel of the scattering of two appropriate ordinary mesons, of momenta p and q, we search for a corresponding pole in four-point correlation functions of quark-bilinear operators ji j ≡ qi q j interpolating the incoming and outgoing mesons Mi j, with decay constants fMij : 0| ji j|Mi j ≡ fMij 0
Summary
The multiquark hadrons, such as tetraquarks (mesonic bound states of two antiquarks and two quarks) and pentaquarks (baryonic bound states of four quarks and one antiquark), form, from both the theoretical and the experimental points of view, one of the most challenging riddles in hadron phenomenology. For obvious reasons, with the mesonic and simpler case of tetraquarks, we approach this issue by investigating the manifestation of tetraquark mesons as intermediate states in scattering reactions of two ordinary mesons into two ordinary mesons in form of contributions of (narrow-width) poles to the associated scattering amplitudes [1,2,3,4,5,6]. We invoke QCD in some well-defined disguise, to gain qualitative access to principal features of selected variants of tetraquarks discriminated basically by the flavour of their quark and antiquark constituents
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
