0000000000504659
AUTHOR
Nikolai Kochelev
Gluonic components of the pion and the transition form factor gamma*gamma* -> pi(0)
We propose an effective lagrangian for the coupling of the neutral pion with gluons whose strength is determined by a low energy theorem. We calculate the contribution of the gluonic components arising from this interaction to the pion transition form factor γ∗γ∗→π0 using the instanton liquid model to describe the QCD vacuum. We find that this contribution is large and might explain the anomalous behavior of the form factor at large virtuality of one of the photons, a feature which was recently discovered by the BaBar Collaboration.
DIS structure functions and the double-spin asymmetry inρ0electroproduction within a Regge approach
The proton, neutron and deuteron structure functions ${F}_{2}{(x,Q}^{2})$ and ${g}_{1}{(x,Q}^{2}),$ measured at intermediate ${Q}^{2},$ are analyzed within a Regge approach. This analysis serves to fix the parameters of this scheme which are then used to calculate, in a unified Regge approach, the properties of ${\ensuremath{\rho}}^{0}$ meson electroproduction on the proton and the deuteron. In this way, the double-spin asymmetry observed at HERMES in ${\ensuremath{\rho}}^{0}$ electroproduction on the proton can be related to the anomalous behavior of the flavor-singlet part of the spin-dependent structure function ${g}_{1}{(x,Q}^{2})$ at small x.
Instantons and the delta I = 1/2 rule
The instanton induced interaction leads to a significant enhancement of the A0 weak amplitude determining the ΔI=1/2 rule, through the contribution of operators with dimension d=9, as we show in the weak K→ππ decay.
New anomalous trajectory in Regge theory
We show that a new Regge trajectory with \alpha_{f_1} (0) \approx 1 and slope \alpha_{f_1}'(0) \approx 0 explains the features of hadron-hadron scattering and photoproduction of the rho and phi mesons at large energy and momentum transfer. This trajectory with quantum numbers P = C = +1 and odd signature can be considered as a natural partner of the Pomeron which has even signature. The odd signature of the new exchange leads to contributions to the spin-dependent cross sections, which do not vanish at large energy. The links between the anomalous properties of this trajectory, the axial anomaly and the flavor singlet axial vector f_1 (1285) meson are discussed.
Mechanism for the double-spin asymmetry in electromagnetic rho production at HERMES
We calculate the contribution of meson and pomeron exchanges to the double-spin asymmetry in $\rho$-meson electromagnetic production at HERMES energies. We show that the observed double-spin asymmetries, which are large, can be explained by the interference between the natural parity $f_2$-secondary Reggeon and the unnatural parity anomalous $f_1$ exchanges.
Triquark correlations and pentaquarks in a QCD sum rule approach
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 $\Theta^+$ 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 $ud\bar{s}$ color quark clusters of 800 MeV and 930 MeV respectively.
Non-perturbative QCD effects in $\eta_c$ and $\eta_b$ decays into baryons and WIMP scattering off nuclei
In this work we estimate the helicity suppressed decay rates of $\eta_b$ resonances into baryon pairs due to instanton-induced effects by rescaling the corresponding partial widths of the experimentally measured branching ratios for the $\eta_c(1S) \to p\bar{p}$ and $\eta_c(1S) \to \Lambda\bar(\Lambda)$ decay modes. Thus we point out that both $\eta_b(1S) \to p\bar{p}$ and $\eta_b(1S) \to \Lambda\bar(\Lambda)$ channels could be detected at a Super B factory and LHC experiments. Furthermore, we examine related instanton-induced effects on WIMP scattering off nuclei concluding, albeit with large uncertainties, that they might enhance the spin-dependent cross section for a light pseudoscalar H…
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.
DIS structure functions and the double-spin asymmetry in rho(0) electroproduction within a Regge approach
The proton, neutron and deuteron structure functions F2(x,Q2) and g1(x,Q2), measured at intermediate Q2, are analyzed within a Regge approach. This analysis serves to fix the parameters of this scheme which are then used to calculate, in a unified Regge approach, the properties of ρ0 meson electroproduction on the proton and the deuteron. In this way, the double-spin asymmetry observed at HERMES in ρ0 electroproduction on the proton, can be related to the anomalous behavior of the flavor-singlet part of the spin-dependent structure function g1(x,Q2) at small x.
Instantons and eta meson production near threshold in NN collisions
An enhancement for the $\eta$ production in proton-neutron collisions as compared with that in proton-proton scattering has been recently observed. We present a calculation for the production cross section, in proton-neutron collisions near threshold, within instanton model for the QCD vacuum and show that a specific flavor dependent nonperturbative quark-gluon interaction related to instantons is able to explain the observed enhancement.
New Anomalous Exchange in Regge Phenomenology and Hard Diffraction
A new mechanism for hard diffraction based on the anomalous $f_1$ trajectory exchange, which we identify as the odd signature partner of the Pomeron, is suggested. We calculate the contribution of the $f_1$ exchange to elastic and dissociative electromagnetic production of vector mesons and show that it gives a dominant contribution to the differential cross sections at large momentum transfers.
QCD sum rule analysis of the pentaquark
We perform a QCD sum rule calculation to determine the mass and the parity of the lowest lying pentaquark state. We include operators up to dimension $d=13$ in the OPE and the direct instanton contributions. We find evidence for a positive parity state. The contribution from operators of dimension $d>5$ is instrumental in determining the parity of the state and achieving the convergence of the sum rule.