Nonlocal quark model beyond mean field and QCD phase transition

A nonlocal chiral quark model is consistently extended beyond mean field using a strict 1/Nc expansion scheme. The parameters of the nonlocal model are refitted to the physical values of the pion mass and the weak pion decay constant. The size of the 1/Nc correction to the quark condensate is carefully studied in the nonlocal and the usual local Nambu-Jona-Lasinio models. It is found that even the sign of the corrections can be different. This can be attributed to the mesonic cut-off of the local model. It is also found that the 1/Nc corrections lead to a lowering of the temperature of the chiral phase transition in comparison with the mean-field result. On the other hand, near the phase transition the 1/Nc expansion breaks down and a non-perturbative scheme for the inclusion of mesonic correlations is needed in order to describe the phase transition point.Comment: 4 pages, 4 figures, talk at the 3rd Joint International Hadron Structure'09 Conference, Tatranska Strba (Slovak Republic), Aug. 30-Sept. 3, 200

Off-diagonal quark distribution functions of the pion within an effective single instanton approximation

We develop a relativistic quark model for pion structure, which incorporates the non-trivial structure of the vacuum of Quantum Chromodynamics as modelled by instantons. Pions are boundstates of quarks and the strong quark-pion vertex is determined from an instanton induced effective lagrangian. The interaction of the constituents of the pion with the external electromagnetic field is introduced in gauge invariant form. The parameters of the model, i.e., effective instanton radius and constituent quark masses, are obtained from the vacuum expectation values of the lowest dimensional quark and gluon operators and the low-energy observables of the pion. We apply the formalism to the calculation of the pion form factor by means of the isovector nonforward parton distributions and find agreement with the experimental data.Comment: LaTeX; altered version; references and figures added. Published: paper has been accepted for publication in Nucl. Phys.

Non-minimal Wu-Yang monopole

We discuss new exact spherically symmetric static solutions to non-minimally extended Einstein-Yang-Mills equations. The obtained solution to the Yang-Mills subsystem is interpreted as a non-minimal Wu-Yang monopole solution. We focus on the analysis of two classes of the exact solutions to the gravitational field equations. Solutions of the first class belong to the Reissner-Nordstr{\"o}m type, i.e., they are characterized by horizons and by the singularity at the point of origin. The solutions of the second class are regular ones. The horizons and singularities of a new type, the non-minimal ones, are indicated.Comment: 10 pages, no figures, typos correcte

π+\pi^+ and π0\pi^0 Polarizabilities from {γγ→ππ\gamma\gamma\rightarrow\pi\pi} Data on the Base of S-Matrix Approach

We suggest the most model-independent and simple description of the $\gamma\gamma\rightarrow\pi\pi$ process near threshold in framework of S-matrix approach. The amplitudes contain the pion polarizabilities and rather restricted information about $\pi \pi$ interaction. Application of these formulae for description of MARK-II \cite{M2} and Crystal Ball \cite{CB} data gives: $(\alpha-\beta)^{C}=(6.0\pm 1.2)\cdot 10^{-42} {\rm cm}^{3}$, $(\alpha-\beta)^{N}=(-1.4\pm 2.1)\cdot 10^{-42} cm^3$ (in units system $e^2 = 4 \pi \alpha$) at the experimental values of $\pi \pi$ scattering lengths. Both values are compartible with current algebra predictions.Comment: LaTeX, 14 pages plus 6 figures (not included, available upon request) , ISU-IAP.Th93-03, Irkuts

Non-Abelian Magnetized Blackholes and Unstable Attractors

Fluctuations of non-Abelian gauge fields in a background magnetic flux contain tachyonic modes and hence the background is unstable. We extend these results to the cases where the background flux is coupled to Einstein gravity and show that the corresponding spherically symmetric geometries, which in the absence of a cosmological constant are of the form of Reissner-Nordstrom blackholes or the AdS_2xS^2, are also unstable. We discuss the relevance of these instabilities to several places in string theory including various string compactifications and the attractor mechanism. Our results for the latter imply that the attractor mechanism shown to work for the extremal Abelian charged blackholes, cannot be applied in a straightforward way to the extremal non-Abelian colored blackholes.Comment: 23 pages, 3 .eps figures; v2: Stability of minimal charge blackhole emphasized, Refs adde

Finite-size effects on the chiral phase diagram of four-fermion models in four dimensions

We study the size dependence of the dynamical symmetry breaking in the four-dimensional Nambu-Jona-Lasinio model. We show that the presence of boundaries reduces the chiral breaking region, and this effect is strengthened for a larger number of compactified dimensions. A critical value for the length of the compactified dimensions exists, below which the dynamical symmetry breaking is not possible. Considering finite temperature and chemical potential, the chiral phase structure for the system with compactified dimensions is obtained. A gradual decreasing of the chiral breaking region with increasing of chemical potential is found. Also, at fixed chemical potential, the decreasing of the size of the system changes the order of the chiral phase transition.Comment: LATEX 14 pages 2 figure

Network-Centric Control Technology of Data Transfer by Network Communications

Рассмотрен вопрос необходимости проведения компьютерного моделирования современных сетевых коммуникаций и использования новых моделей и интеллектуального управления в целях повышения безопасности и качества работы сети передачи данных и связи, особенно в сложных условиях.The purpose. The project is based on applied research in the field of highspeed cycles control systems for net-centric dynamic application processes with spatially-distributed interrelated functional components. Thus it provides functional and temporal combination of internal resources of net-centric distributed control systems with objects and technological processes on the basis of shared use of dynamics models working in an accelerated time scale into a single space-time net-centric complex.Мета роботи — дослідити фундаментальні основи та принципи побудови нових перспективних систем контролю передачі інформаційно-комунікаційних даних в мережі на основі застосування мережецентричних технологій, що дозволить істотно розширити перелік вирішуваних в реальному масштабі часу задач розподіленого керування швидкісними циклами прикладних процесів та підвищити якість, надійність та безпеку роботи мережевих систем взагалі

Stability of Driven Josephson Vortex Lattice in Layered Superconductors Revisited

We analytically study stability of sliding lattice of Josephson vortices driven by a transport current in the stack direction in strong in-plane magnetic field. In contrast to recent findings we obtain that there are no diverse configurations of stable vortex lattices, and, hence, the stable sliding vortex lattice can not be selected by boundary conditions. We find that only the triangular (rhombic) lattice can be stable, its stability being limited by a critical velocity value. At higher velocities there are no simple stable lattices with single flux line per unit cell. Oblique sliding lattices are found to be never stable. Instability of such lattices is revealed beyond the linear approximation in perturbations of the lattice.Comment: 11 pages, 2 figures, RevTeX 4, Submitted to Phys. Rev.