Narrow Results

We perform the first study for the bound states of colored scalar particles ϕ (“scalar quarks”) in terms of mass generation with quenched SU(3)_c lattice QCD. We investigate the bound states of ϕ, ϕ^†ϕ and ϕϕϕ (“scalar-quark hadrons”), as well as the bound states of ϕ and quarks ψ, i.e., ϕ^†ψ, ψψϕ and ϕϕψ (“chimera hadrons”). All these new-type hadrons including ϕ have a large mass of several GeV due to large quantum corrections by gluons, even for zero bare scalar-quark mass m_ϕ = 0 at a⁻¹ ~ 1GeV. We find a similar m_ψ-dependence between ϕ^†ψ and ϕϕψ, which indicates their similar structure due to the large mass of ϕ. From this study, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluons.

In the framework of the quasiparticle approach, the ground state mass of heavy pentaquarks have been investigated in diquark–diquark–antiquark picture and the higher states are investigated in the mass loaded flux tube model where two light diquarks are supposed to be linked by a flux tube to the heavy quark. The Regge trajectories for heavy pentaquarks have been studied. The Regge slope (α) of these particles have been obtained as ≈1 GeV² which indicates that the Regge trajectory follows the linearity conditions with universal value of α (~ 1 GeV²). The ground state mass of doubly charm and doubly bottom baryons like have also been investigated in quasiparticle approach. The results are found to be in reasonably good agreement with the experimental and other theoretical estimates.

The baryonic decays of J/ψ provide a new way to study the internal structure of baryons. A simple diquark model applied to the calculation of the decay cross-sections is compared with the ordinary constituent quark model. Various models also give different predictions for the rates involving the N*(1440) resonance in the final state.

QCD instantons generate non-perturbative spin- and flavor- dependent correlations between light quarks. We report on the results of a series of studies on the contribution of instantons to the electro-weak structure of light hadrons. We show that the Instanton Liquid Model can reproduce the available data on proton and pion form factors at large momentum transfer, and explain the delay of the onset of the perturbative regime in some exclusive reactions. We provide unambiguous evidence that instantons lead to the formation of a deeply bound scalar, color anti-triplet diquark, with a mass of about 450 MeV. The strong attraction in the , scalar diquark channel leads to a quantitative description of non-leptonic decays of hyperons and provides a microscopic dynamical explanation of the Δ I = 1/2 rule.

The behavior of the mesons and diquarks is studied at finite temperatures, chemical potentials and densities, notably when the color superconductivity is taken into account. The Nambu and Jona-Lasinio model complemented by a Polyakov loop (PNJL description) has been adapted in order to model them in this regime. This paper focuses on the scalar and pseudoscalar mesons and diquarks, in a three-flavor and three-color description, with the isospin symmetry and at zero strange density. An objective of this work is to underline the modifications carried out by the color superconducting regime on the used equations and on the obtained results. It has been observed that the two-flavor color-superconducting (2SC) phase affects the masses and the coupling constants of the mesons and diquarks in a non-negligible way. This observation is particularly true at high densities and low temperatures for the pions, $\eta$ and the diquarks [ud] whose color is rg. This reveals that the inclusion of the color superconductivity in the modeling is relevant to describe the mesons and diquarks near the first-order chiral phase transition.

The deep inelastic scattering of neutrinos on unpolarized nucleons is considered in a generalized parton model which takes into account quark-clustering effects, modeled by diquarks. The diquark contributions are expected to be significant at small Q² values and to vanish asymptotically, and describe phenomenologically higher twist corrections. The most general case is studied, which includes both scalar and pseudovector diquarks inside the nucleons, as well as the contribution of scalar–vector and vector–scalar transitions. The resulting scaling violations are briefly discussed.

In this contribution, we present for the first time a scenario according to which early quark deconfinement in compact stars is triggered by the Bose-Einstein condensation (BEC) of a light sexaquark (S) with a mass m_S < 2054 MeV, that has been suggested as a candidate particle to explain the baryonic dark matter in the universe. The onset of S BEC marks the maximum mass of hadronic neutron stars and it occurs when the condition for the baryon chemical potential μ_b = m_S/2 is fulfilled in the center of the star, corresponding to M_onset < 0.7M_⊙. In the gravitational field of the star the density of the BEC of S increases until a new state of the matter is attained, where each of the S-states got dissociated into a triplet of color-flavor-locked (CFL) diquark state. These diquarks are the Cooper pairs in the color superconducting CFL phase of quark matter, so that the developed scenario corresponds to a BEC–BCS transition in strongly interacting matter. For the description of the CFL phase, we develop here for the first time the three-flavor extension of the density-functional formulation of a chirally symmetric Lagrangian model of quark matter where confining properties are encoded in a divergence of the scalar self-energy at low densities and temperatures.

As an example for exclusive near threshold meson production, we investigate the production of the pseudo-scalar η meson in a microscopic meson exchange (MECM) and in a relativistic quark model, based on a gluon or instanton pair creation (RQM). We describe the baryons as covariant quark – scalar diquark systems with harmonic confinement; the excitation of intermediate baryon resonances is accounted for by meson or by colorless 2-gluon (Pomeron) exchange in the MECM and RQM, respectively. We find that both models account for the energy dependence of the total cross section near the η threshold, reflecting the dominance of the S₁₁(1535) baryon resonance. As a more stringent test we propose the recoilless excitation of the η meson in nuclei.

The quark shell model has been successful in describing properties of hadrons. Because of color the quark shell model with 3n valence quarks has many more states which are singlet in color than the nuclear shell model with n valence nucleons. However, the quark interaction has been shown to favor two quarks coupled to spin zero and isospin zero and color , called diquarks. We show that the color singlet states in the quark shell model which have the maximal number of diquarks consistent with the Pauli symmetry are in one to one correspondence with the states of the nuclear shell model. We also investigate the implications of the quark interactions on the nuclear shell model interaction.