Form Factor of the Two Fermions Bound State: The Case of Equal Masses and Vector Currentl

New form factor components of two relativistic with equal masses fermions bound state in the case of a vector current are obtained. Consideration is performed within the framework of the relativistic quasipotential approach on the basis of covariant Hamiltonian formulation of quantum field theory by transition to three-dimensional relativistic configurational representation in the case of two relativistic particles with equal masses and spin 1/2.

Heavy Tetraquarks in the Relativistic Quark Model

We give a review of the calculations of the masses of tetraquarks with two and four heavy quarks in the framework of the relativistic quark model based on the quasipotential approach and QCD. The diquark-antidiquark picture of heavy tetraquarks is used. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. Diquarks are considered in the colour triplet state. It is assumed that the diquark and antidiquark interact in the tetraquark as a whole and the internal structure of the diquarks is taken into account by the calculated form factor of the diquark-gluon interaction. All parameters of the model are kept fixed from our previous calculations of meson and baryon properties. A detailed comparison of the obtained predictions for heavy tetraquark masses with available experimental data is given. Many candidates for tetraquarks are found. It is argued that the structures in the di-J/ψ mass spectrum observed recently by the LHCb collaboration can be interpreted as ccc¯c¯ tetraquarks.

On Threshold Resummation S-Factor for a System of Two Relativistic Spinor Particles with Arbitrary Masses

We present a new threshold resummation S-factor obtained for a composite system of two relativistic spin 1/2 particles of arbitrary masses interacting via a Coulomb-like chromodynamical potential. The analysis is performed in the framework of a relativistic quasipotential approach in the Hamiltonian formulation of the quantum field theory in the relativistic configuration representation. The pseudoscalar, vector, and pseudovector systems are considered. The difference in the behavior of the S-factor for these cases is discussed. A connection between the new and the previously obtained S-factors for spinless particles of arbitrary masses and relativistic spinor particles of equal masses is established.

Semileptonic Decays of Heavy Baryons in the Relativistic Quark Model

Semileptonic and rare semileptonic decays of heavy baryons are studied in the framework of the relativistic quark model based on the quark-diquark picture, quasipotential approach, and quantum chromodynamics (QCD). The form factors parametrizing the matrix elements of the weak transitions are calculated in the whole accessible kinematical range with the comprehensive account of the relativistic effects. The obtained results for the branching ratios and other observables agree well with the available experimental data.