The nucleons were considered as point-like particles when they were first isolated in the 30’s and later on they were found to have extended structure in the 50’s. The quark model suggested the nucleons as composite systems of more basic constituents of quarks and the lepton nucleon deep elastic scattering experiments in the latter 60’s confirmed the quarkparton structure of nucleons and led to...

We perform an analysis of semi-inclusive production of charm (D-mesons) in neutral current (NC) and charged current (CC) deep inelastic scattering (DIS) at full O(α s). Our calculation is based on the heavy quark scheme developed by Aivazis, Collins, Olness and Tung (ACOT) where we include anO(α s) calculation of quark scattering contributions for general masses and couplings. We review the rel...

The electromagnetic interaction with quarks is investigated through a relativis-tic, electromagnetic gauge-invariant treatment. Gluon dressing of the quark-photon vertex and the quark self-energy functions is described by the inhomogeneous Bethe-Salpeter equation in the ladder approximation and the Schwinger-Dyson equation in the rainbow approximation respectively. Results for the calculation o...

The partial restoration of chiral symmetry in nuclear medium is investigated in a model independent way by exploiting operator relations in QCD. An exact sum rule is derived for the quark condensate valid for all density. This sum rule is simplified at low density to a new relation 〈q̄q〉∗/〈q̄q〉 = (F t π/Fπ)Z ∗1/2 π with the in-medium quark condensate 〈q̄q〉 ∗, in-medium pion decay constant F t π an...

In the presence of a large parameter, such as mass or energy, leading behavior of individual Feynman diagrams often get cancelled in the sum. This is known to happen in large-Nc QCD in the presence of a baryon, and also in the case of high-energy electron-electron as well as quark-quark scatterings. We present an exact combinatorial formula, involving multiple commutators of the vertices, which...

We report on an attempt to describe hard exclusive photoproduction of J/Ψ mesons, i.e. the reaction γp → J/Ψp, by means of a modified version of the hard-scattering approach, in which the proton is treated as a quark-diquark rather than a three-quark system. In order to improve the applicability of the model at momentum transfers of only a few GeV we take into account constituent-mass effects i...

We assess transport properties of heavy quarks in the Quark-Gluon Plasma (QGP) that show a strong non-perturbative behavior. A T-matrix approach based on a potential taken from lattice QCD hints at the presence of heavy-quark (HQ) resonant scattering with an increasing strength as the temperature, T , reaches the critical temperature, Tc ' 170 MeV for deconfinement from above. The implementatio...

Hadron spectra measured at intermediate transverse momenta, pT=2-6GeV, in 200AGeV Au-Au collisions at the Relativistic Heavy-Ion Collider (RHIC) have revealed a surprisingly large baryon-tomeson ratio ~1 and a so-called constituent quark-number scaling (CQNS) of the elliptic flow, v2(pT). Both phenomena are rather naturally explained within quark coalescence models (QCMs), where constituent qua...

A new mechanism for single spin asymmetries in strong interaction is proposed. It is based on instanton–induced nonperturbative chromomagnetic quark–gluon interaction. We estimate the contribution of this interaction to single spin asymmetry in quark–quark scattering. It is shown, that interference between quark spin–flip amplitude induced by instantons and spin–nonflip amplitude, which is rela...

Using a Lagrangian which contains quarks as elementary degrees of freedom and mesons as bound states, a transport formalism is developed, which allows for a dynamical transition from a quark plasma to a state, where quarks are bound into hadrons. Simultaneous transport equations for both particle species are derived in a systematic and consistent fashion. For the mesons a formalism is used whic...