A phenomenological interpretation of open charm production at HERA in terms of the semi-hard approach

In the framework of the semi-hard (k_t-factorization) approach, we analyze the various charm production processes in the kinematic region covered by the HERA experiments.Comment: DESY 02-017, LUNFD6/(NFFL--7209) 200

Unconventional magnetoresistance in long InSb nanowires

Magnetoresistance in long correlated nanowires of degenerate semiconductor InSb in asbestos matrix (wire diameter of around 5 nm, length 0.1 - 1 mm) is studied over temperature range 2.3 - 300 K. At zero magnetic field the electric conduction $G$ and the current-voltage characteristics of such wires obey the power laws $G\propto T^\alpha$, $I\propto V^\beta$, expected for one-dimensional electron systems. The effect of magnetic field corresponds to a 20% growth of the exponents $\alpha$, $\beta$ at H=10 T. The observed magnetoresistance is caused by the magnetic-field-induced breaking of the spin-charge separation and represents a novel mechanism of magnetoresistance.Comment: To be published in JETP Letters, vol. 77 (2003

Strong-Pinning Effects in Low-Temperature Creep: Charge-Density Waves in TaS_3

Nonlinear conduction in the quasi-one dimensional conductor o-TaS_3 has been studied in the low-temperature region down to 30 mK. It was found that at temperatures below a few Kelvins the current-voltage (I-V) characteristics consist of several branches. The temperature evolution of the I-V curve proceeds through sequential freezing-out of the branches. The origin of each branch is attributed to a particular strong pinning impurity type. Similar behavior is expected for other physical systems with collective transport (spin-density waves, Wigner crystals, vortex lattices in type-II superconductors etc.) in the presence of strong pinning centers.Comment: 11 pages, 3 ps figures, Revtex, To be published in Phys. Rev. Letters (1997

Elliptic Schlesinger system and Painlev{\'e} VI

We construct an elliptic generalization of the Schlesinger system (ESS) with positions of marked points on an elliptic curve and its modular parameter as independent variables (the parameters in the moduli space of the complex structure). ESS is a non-autonomous Hamiltonian system with pair-wise commuting Hamiltonians. The system is bihamiltonian with respect to the linear and the quadratic Poisson brackets. The latter are the multi-color generalization of the Sklyanin-Feigin-Odeskii classical algebras. We give the Lax form of the ESS. The Lax matrix defines a connection of a flat bundle of degree one over the elliptic curve with first order poles at the marked points. The ESS is the monodromy independence condition on the complex structure for the linear systems related to the flat bundle. The case of four points for a special initial data is reduced to the Painlev{\'e} VI equation in the form of the Zhukovsky-Volterra gyrostat, proposed in our previous paper.Comment: 16 pages; Dedicated to the centenary of the publication of the Painleve VI equation in the Comptes Rendus de l'Academie des Sciences de Paris by Richard Fuchs in 190

Region of Excessive Flux of PeV Cosmic Rays in the Direction Toward Pulsars PSR J1840+5640 and LAT PSR J1836+5925

An analysis of arrival directions of extensive air showers (EAS) registered with the EAS MSU and EAS-1000 prototype arrays has revealed a region of excessive flux of PeV cosmic rays in the direction toward pulsars PSR J1840+5640 and LAT PSR J1836+5925 at significance level up to 4.5sigma. The first of the pulsars was discovered almost 30 years ago and is a well-studied old radio pulsar located at the distance of 1.7pc from the Solar system. The second pulsar belongs to a new type of pulsars, discovered by the space gamma-ray observatory Fermi, pulsations of which are not observed in optical and radio wavelengths but only in the gamma-ray range of energies (gamma-ray-only pulsars). In our opinion, the existence of the region of excessive flux of cosmic rays registered with two different arrays provides a strong evidence that isolated pulsars can give a noticeable contribution to the flux of Galactic cosmic rays in the PeV energy range.Comment: 14 pages; v.2: a few remarks to match a version accepted for Astronomy Letters added. They can be found by redefining the \NEW command in the preamble of the LaTeX fil

Charm photoproduction at HERA: kt-factorization versus experimental data

We calculate the cross section of charm photoproduction at HERA collider in the framework of the kt-factorization QCD approach. Our analysis cover the inclusive charm production as well as charm and associated jet production processes. Both photon-gluon and gluon-gluon fusion mechanisms are taken into account. The unintegrated gluon densities in a proton and in a photon obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription are used. Our theoretical results are compared with the recent experimental data taken by the H1 and ZEUS collaborations at HERA. Special attention is put on the specific angular correlations which can provide unique information about non-collinear gluon evolution dynamics.Comment: 33 pages, 15 figures, 2 table

Prompt photon photoproduction at HERA in the k_T-factorization approach

We present calculations of the prompt photon photoproduction at HERA collider in the k_T-factorization approach. Both direct and resolved contributions are taken into account. The conservative error analisys is performed. The unintegrated parton densities in a proton and in a photon are determined using the Kimber-Martin-Ryskin prescription. We investigate both inclusive and associated with jet prompt photon photoproduction rates. In particular, we study the angular correlations between produced photon and hadronic jet in the transverse momentum plane which can provide a unique information about non-collinear evolution dynamics. We compare our theoretical predictions with recent experimental data taken by the H1 and ZEUS collaborations.Comment: 34 pages, 18 figure

Impurity-induced stabilization of Luttinger liquid in quasi-one-dimensional conductors

It is shown theoretically that the Luttinger liquid phase in quasi-one-dimensional conductors can exist in the presence of impurities in a form of a collection of bounded Luttinger liquids. The conclusion is based upon the observation by Kane and Fisher that a local impurity potential in Luttinger liquid acts, at low energies, as an infinite barrier. This leads to a discrete spectrum of collective charge and spin density fluctuations, so that interchain hopping can be considered as a small parameter at temperatures below the minimum excitation energy of the collective modes. The results are compared with recent experimental observation of a Luttinger-liquid-like behavior in thin NbSe$_3$ and TaS$_3$ wires.Comment: 11 pages, revtex, final version published in JETP Lett

Production of electroweak gauge bosons in off-shell gluon-gluon fusion

We study the production of electroweak gauge bosons at high energies in the framework of kt-factorization QCD approach. Contributions from the valence quarks are calculated using the quark-gluon interaction and quark-antiquark annihilation QCD subprocesses. The total and differential cross sections (as a function of the transverse momentum and rapidity) are presented and the ratio of cross sections for W and Z boson production is investigated. The conservative error analysis is performed. In the numerical calculations two different sets of unintegrated gluon distributions in the proton are used: the one obtained from Ciafaloni-Catani-Fiorani-Marchesini evolution equation and the other from Kimber-Martin-Ryskin prescription. Theoretical results are compared with experimental data taken by the D0 and CDF collaborations at the Tevatron. We demonstrate the importance of the quark component in parton evolution in description of the experimental data. This component is very significant also at the LHC energies.Comment: 33 pages, 18 figure