Nikolai Kochelev

The physics of glueballs

Glueballs are particles whose valence degrees of freedom are gluons and therefore in their description the gauge field plays a dominant role. We review recent results in the physics of glueballs with the aim set on phenomenology and discuss the possibility of finding them in conventional hadronic experiments and in the Quark Gluon Plasma. In order to describe their properties we resort to a variety of theoretical treatments which include, lattice QCD, constituent models, AdS/QCD methods, and QCD sum rules. The review is supposed to be an informed guide to the literature. Therefore, we do not discuss in detail technical developments but refer the reader to the appropriate references.

Anomalous quark chromomagnetic moment induced by instantons

Abstract It is shown that the instanton-induced quark–gluon interaction leads to the quark anomalous chromomagnetic moment. In the instanton-liquid model for the QCD vacuum, the chromomagnetic moment is μ a =− πf /2 α s , where f is the packing fraction of instantons in the vacuum. A new mechanism for single spin asymmetries in strong interaction based on instanton-induced chromomagnetic quark-gluon interaction is proposed.

Anomalous quark chromomagnetic moment and single-spin asymmetries

Abstract We discuss a nonperturbative mechanism for the single-spin asymmetries in the strong interaction. This mechanism is based on the existence of a large anomalous quark chromomagnetic moment induced by the nontrivial topological structure of QCD vacuum. Our estimations within the instanton liquid model for QCD vacuum show that AQCM generates very large SSA on the quark level. Therefore, this mechanism can be responsible for the anomalously large SSA observed in different high energy reactions with hadrons.

Triquark correlations and pentaquarks in a QCD sum rule approach

Abstract The role of quark correlations in the description of hadron dynamics in many domains of physics, from low energy dynamics to very hot (dense) systems, is being appreciated. Strong correlations of two quarks (diquark) have been widely investigated in this respect. Recently, we have proposed a dynamical scheme to describe the Θ + pentaquark in which also three quark correlations (triquark) were instrumental in producing a low mass exotic state. We perform a study, within the QCD sum rule approach including OPE and direct instanton contributions, of triquark correlations and obtain two quasi-bound light u d s ¯ color quark clusters of 800 and 930 MeV, respectively.

The Pauli form factor of the quark induced by instantons

Abstract The non-perturbative contribution to the Pauli form factor of the quark, F 2 ( Q 2 ), is calculated within an instanton model for the QCD vacuum. It is shown that the instantons give a large negative contribution to the form factor.

Instantons and polarized structure functions

The contribution of the quark-quark and quark-gluon interaction induced by instantons to the valence quark and proton spin-dependent structure functions

On the pi pi contribution to the QCD sum rules for the light tetraquark

g_1(x,Q^2)

Pomeron fusion and central η and η′ meson production

is estimated within the instanton liquid model for QCD vacuum. It is shown, that this interaction leads to a rather large violation of the Ellis-Jaffe sum rule.

Role of anomalous chromomagnetic interaction in Pomeron and Odderon structures and in gluon distribution

We perform a QCD sum rule analysis for the f{sub 0} light tetraquark taking into account the contribution arising from the two pion intermediate state. With the interpolating currents of the different chiral combinations of scalar and pseudoscalar diquarks, it is demonstrated that the interpolating current with maximum chirality has a large coupling to the two pion state, but the current with zero chirality interacts only weekly with this state. Taking into account the form factor in the f{sub 0}-two pion vertex, it is shown that the f{sub 0} coupling to the two pion state leads to an increase of the lightest tetraquark mass by a value of about 100 MeV. The analysis of the resulting sum rule shows that the {sigma}(f{sub 0}(600))-meson state might be treated as the four-quark bound state in the instanton field which has a rather strong coupling to the two pion state.

Single Spin Asymmetries in High Energy Reactions and Nonperturbative QCD Effects

Abstract The contribution of pomeron fusion to the cross section of η and η ′ productions in double-diffractive scattering has been calculated within the Donnachie-Landshoff model of pomeron. It is shown that the double pomeron exchange mechanism does not explain the full set of the recent data of WA102 Collaboration, though it might not be inconsistent with η ′ productions.