Dynamical Approach to Decays of XYZ States

We review the existing results on the exotic XYZ states and their decays obtained within the confined covariant quark model. This dynamical approach is based on a non-local Lagrangian of hadrons with quarks, has built-in quark confinement, and is suited well for the description of different multiquark states, including the four quark ones. We focus our analysis on the various decay modes of five exotic states, X ( 3872 ) , Z c ( 3900 ) , Y ( 4260 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) , aiming to clarify their internal quark structures. By considering mostly branching fractions and decay widths using the molecular-type or the tetraquark-type interpolating currents, conclusions about the nature of these particles are drawn: the molecular structure is favored for Z c ( 3900 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) and the tetraquark for X ( 3872 ) and Y ( 4260 ) .

Quark model calculations of transition form factors at high photon virtualities

We present calculations of γ*N → N* transition form factors, where N is the nucleon and N* is a nucleon resonance, based on a covariant quark model. Our main focus is at high photon virtualities (large Q2) where the valence quark degrees of freedom dominate the contributions to the transition form factors and helicity amplitudes. In that regime, the quark model estimates can be compared with the available data, particularly with the Jefferson Lab data at intermediate and large momentum transfer (Q2 > 2 GeV2). The main focus is on the Δ(1232)3/2+, N(1440)1/2+, N(1535)1/2- and N(1520)3/2- resonances, but estimates for other higher mass resonances are also discussed.

Dalitz Decays of Unflavored Mesons in the Poincaré Covariant Quark Model

The procedure for obtaining the radiative decay constants of pseudoscalar and vector unflavored mesons in the point-form of PiQM is presented. Based on the obtained earlier parameters of the model for light (u, d, s) quarks, we obtain the remaining parameters from the experiments on the V → Py and P → Vy decays. As a result, the mixing angles for pseudoscalar and vector mesons and the behavior of the V → Pℓ+ℓ− decay constant are obtained in agreement with modern experimental data.

Poincaré-covariant quark model of electroweak light mesons decays

The procedure for obtaining the radiative decay constants of pseudoscalar and vector unflavored mesons in point–form of Poincaré-invariant quantum mechanics is presented. In the course of the work the authors determine the remaining parameters from V → Pγ and P → Vγ experimental decay value, using the obtained earlier parameters of the model for light (u, d and s) quarks. As a result, the mixing angles for pseudoscalar and vector meson sector were obtained taking into account gluonium content for η – η′ meson sector.