Superconducting phase transition in the Nambu - Jona-Lasinio model

The Nambu - Bogoliubov - de Gennes method is applied to the problem of superconducting QCD. The effective quark-quark interaction is described within the framework of the Nambu - Jona-Lasinio model. The details of the phase diagram are given as a function of the strength of the quark-quark coupling constant $G^{\prime}$. It is find that there is no superconducting phase transition when one uses the relation between the coupling constants $G^{\prime}$ and $G$ of the Nambu - Jona-Lasinio model which follows from the Fierz transformation. However, for other values of $G^{\prime}$ one can find a rich phase structure containing both the chiral and the superconducting phase transitions.Comment: 7 pages, 3 figure

Evidence of strong higher twist effects in diffractive DIS at HERA at moderate Q2

We study a twist decomposition of diffractive structure functions in the diffractive deep inelastic scattering (DDIS) at HERA. At low Q2 and at large energy the data exhibit a strong excess, up to about 100%, above the twist 2 NLO DGLAP description. The excess in consistent with higher twist effects. It is found, that complementing the DGLAP fit by twist 4 and 6 components of the GBW saturation model leads to a good description of data at low Q2. We conclude that the DDIS at HERA provides the first, strong evidence of higher twist effects in DIS.Comment: 4 pages, 2 PDF figure

Coexistence of pion condensation and color superconductivity in two flavor quark matter

We show that the superconducting 2SC phase at high density and normal chiraly broken quark phase at low density is separated by the mixed non-uniform phase along the baryon density line.Comment: Change of the title. Journal-ref adda

Evidence for breakdown of the DGLAP description in diffractive DIS at HERA

HERA data on diffractive DIS show deviations from twist 2 DGLAP predictions below $Q^2\sim 5$ GeV$^2$ at low pomeron $\xi$, which may reach up to 100%. These deviations are consistent with higher twists effects extracted from the saturation model. It is a first direct evidence for the higher twists in DIS. This finding affects determination of the diffractive parton densities that are used for the predictions at the LHC.Comment: 5 pages, 2 figures, Based on the talk presented at the conference Deep-Inelastic Scattering and Related Subjects (DIS2012), Bonn, 201

Isgur - Wise Functions for Confined Light Quarks in a Colour Electric Potential

We explore the influence on the Isgur-Wise function of the colour electric potential between heavy and light quarks in mesons. It is shown that in bag models, its inclusion tends to restore light quark flavour symmetry relative to the MIT bag predictions, and that relative to this model it flattens the Isgur-Wise function. Results compare very well with observations.Comment: 9 pages, 1 figure (available upon request), Latex, TPJU - 4/9

Exclusive ηc\eta_c photo- and electroproduction at HERA as a possible probe of the odderon singularity in QCD

Theory and phenomenology of the eta_c photo- and electroproduction is developed from the point of view of probing the odderon singularity in QCD which corresponds to the three gluon exchange mechanism. This mechanism leads to the cross-sections which are independent of W^2 for the exchange of three non-interacting gluons or exhibit increase with increasing W^2 (or 1/x) for the odderon intercept above unity. The \eta_c electroproduction in the three gluon exchange mechanism is shown to be entirely controlled by the transversely polarised virtual photons. The magnitude of the eta_c photoproduction cross-section is estimated to be around 11-45pb. The t-dependence of the differential cross-section is also discussed.Comment: 9 pages, LaTeX, uses epsfig.sty; Numerical error corrected. A factor of 1/3 missing in amplitude in Eq.(8) added. Obtained gamma p -> eta_c p cross-section smaller by a factor of 9 than in the original version of the paper. Figures 4 and 5 changed accordingl

Meson bound states in multiflavour massive Schwinger model

The problem of meson bound states with $N_f$ massive fermions in two dimensional quantum electrodynamics is discussed. We speculate about the spectrum of the lightest particles by means of the effective semiclassical description. In particular, the systems of fundamental fermions with $SU(2)$ and $SU(3)$ flavour symmetries broken by massive terms are investigated.Comment: 16 page