Exclusive diffractive electroproduction of dijets in collinear factorization

Exclusive electroproduction of hard dijets can be described within the collinear factorization. This process has clear experimental signature and provides one with an interesting alternative venue to test QCD description of hard diffractive processes and extract information on generalized nucleon parton distributions. In this work we present detailed leading-order QCD calculations of the relevant cross sections, including longitudinal momentum fraction distribution of the dijets and their azimuthal angle dependence.Comment: 11 pages, 14 Postscript figures, uses revtex4.st

Heavy-to-light form factors in the quark model with heavy propagators

We calculate the heavy-to-light form factors in the relativistic quark model with heavy infrapropagators. Their q^2-dependence in the physical region is defined by two parameters: the "infrared" parameter \nu characterizing the infrared behavior of the heavy quark and the mass difference of the heavy meson and heavy quark E=m_H-M_Q. It is found that the values of the D\to K(K^*) and D\to \pi(\rho) form factors at q^2=0 are in excellent agreement with the available experimental data and other approaches whereas these values for B\to \pi(\rho) transitions are found to be larger than those of several other models. The obtained form factors are used to calculate the widths of the semileptonic decays of B and D mesons. The comparison of our results with the available experimental data and other approaches is givenComment: 15 pages, 3 eps figures. New references are added, corrected some typos. To appear in Few-Body System

Electroproduction of Soft Pions at Large Momentum Transfers

We consider pion electroproduction on a proton target close to threshold for Q^2 in the region 1-10 GeV^2. The momentum transfer dependence of the S-wave multipoles at threshold, E_{0+} and L_{0+}, is calculated using light-cone sum rules.Comment: 8 pages, 3 figures; Invited talk at the workshop on Exclusive Reactions at High Momentum Transfer, 21-24 May 2007, Newport News, Virginia, U.S.A. and International Conference on hadron Physics TROIA'07, 30 Aug. - 3 Sept. 2007, Canakkale, Turke

Diffractive jets production in pp-collisions

We consider the exclusive diffractive dissociation of a proton into three jets with large transverse momenta in the double-logarithmic approximation of perturbative QCD. This process is sensitive to the proton unintegrated gluon distribution at small x and to the proton light-cone distribution amplitudes. According to our estimates, an observation of such processes in the early runs at LHC is feasible for jet transverse momenta of the order of 5 GeV.Comment: Presented at International Workshop on Diffraction in High-Energy Physics, La Londe-les-Maures, France, September 9 - 14, 200

Multiple Ionization Bursts in Laser-Driven Hydrogen Molecular Ion

Theoretical study on H$_2^+$ in an intense infrared laser field on the attosecond time-scale reveals that the molecular ion shows multiple bursts of ionization within a half-cycle of the laser field oscillation, in contrast to the widely accepted tunnel ionization picture for an atom. These bursts are found to be induced by transient localization of the electron at one of the nuclei, and a relation between the time instants of the localization and the vector potential of the laser light is derived. Furthermore, an experimental scheme is proposed to probe the localization dynamics by an extreme ultraviolet laser pulse.Comment: 5 pages, 4 figure

Towards the theory of coherent hard dijet production on hadrons and nuclei

We carry out a detailed calculation of the cross section of pion diffraction dissociation into two jets with large transverse momenta, originating from a hard gluon exchange between the pion constituents. Both the quark and the gluon contribution are considered and in the latter case we present calculations both in covariant and in axial gauges. We find that the standard collinear factorization does not hold in this reaction. The structure of non-factorizable contributions is discussed and the results are compared with the experimental data. Our conclusion is that the existing theoretical uncertainties do not allow, for the time being, for a quantitative extraction of the pion distribution amplitude.Comment: 45 pages, latex, 17 figures, final version to appear in Nuclear Physics

Group expansions for impurities in superconductors

A new method is proposed for practical calculation of the effective interaction between impurity scatterers in superconductors, based on algebraic properties of related Nambu matrices for Green functions. In particular, we show that the density of states within the s-wave gap can have a non-zero contribution (impossible either in Born and in T-matrix approximation) from non-magnetic impurities with concentration $c \ll 1$, beginning from $\sim c^{3}$ order.Comment: 5 pages, 1 figur