Exchange Field Induced Magnetoresistance in Colossal Magnetoresistance Manganites

The effect of an exchange field on electrical transport in thin films of metallic ferromagnetic manganites has been investigated. The exchange field was induced both by direct exchange coupling in a ferromagnet/antiferromagnet multilayer and by indirect exchange interaction in a ferromagnet/paramagnet superlattice. The electrical resistance of the manganite layers was found to be determined by the absolute value of the vector sum of the effective exchange field and the external magnetic field.Comment: 5 pages, 4 figure

Non-linear BFKL dynamics: color screening vs. gluon fusion

A feasible mechanism of unitarization of amplitudes of deep inelastic scattering at small values of Bjorken $x$ is the gluon fusion. However, its efficiency depends crucially on the vacuum color screening effect which accompanies the multiplication and the diffusion of BFKL gluons from small to large distances. From the fits to lattice data on field strength correlators the propagation length of perturbative gluons is $R_c\simeq 0.2-0.3$ fermi. The probability to find a perturbative gluon with short propagation length at large distances is suppressed exponentially. It changes the pattern of (dif)fusion dramatically. The magnitude of the fusion effect appears to be controlled by the new dimensionless parameter $\sim R_c^2/8B$, with the diffraction cone slope $B$ standing for the characteristic size of the interaction region. It should slowly $\propto 1/\ln Q^2$ decrease at large $Q^2$. Smallness of the ratio $R_c^2/8B$ makes the non-linear effects rather weak even at lowest Bjorken $x$ available at HERA. We report the results of our studies of the non-linear BFKL equation which has been generalized to incorporate the running coupling and the screening radius $R_c$ as the infrared regulator.Comment: 16 pages, 2 figures, version accepted for publication, references adde

Anatomy of the differential gluon structure function of the proton from the experimental data on F_2p

The use of the differential gluon structure function of the proton ${\cal F}(x,Q^{2})$ introduced by Fadin, Kuraev and Lipatov in 1975 is called upon in many applications of small-x QCD. We report here the first determination of ${\cal F}(x,Q^{2})$ from the experimental data on the small-x proton structure function $F_{2p}(x,Q^{2})$. We give convenient parameterizations for ${\cal F}(x,Q^{2})$ based partly on the available DGLAP evolution fits (GRV, CTEQ & MRS) to parton distribution functions and on realistic extrapolations into soft region. We discuss an impact of soft gluons on various observables. The x-dependence of the so-determined ${\cal F}(x,Q^{2})$ varies strongly with Q^2 and does not exhibit simple Regge properties. None the less the hard-to-soft diffusion is found to give rise to a viable approximation of the proton structure function F_{2p}(x,Q^2) by the soft and hard Regge components with intercepts \Delta_{soft}=0 and \Delta_{hard}\sim 0.4.Comment: 37 pages, 25 figure

Jet quenching with running coupling including radiative and collisional energy losses

We calculate the nuclear modification factor for RHIC and LHC conditions accounting for the radiative and collisional parton energy loss with the running coupling constant.We find that the RHIC data can be explained both in the scenario with the chemically equilibrium quark-gluon plasma and purely gluonic plasma with slightly different thermal suppression of the coupling constant. The role of the parton energy gain due to gluon absorption is also investigated. Our results show that the energy gain gives negligible effect.Comment: 11 pages, 3 figure

Diffractive vector mesons beyond the s-channel helicity conservation

We derive a full set, and determine the twist, of helicity amplitudes for diffractive production of light to heavy vector mesons in deep inelastic scattering. For large $Q^{2}$ all helicity amplitudes but the double-flip are calculable in perturbative QCD and are proportional to the gluon structure function of the proton at a similar hard scale. We find a substantial breaking of the $s$-channel helicity conservation which must persist also in real photoproduction.Comment: 7 pages, 1 postscript figure. Discussion of double-flip updated, typos corrected, reference to the ZEUS, H1, HERMES presentations at ICHEP-98 adde

Geometric Scaling in a Symmetric Saturation Model

We illustrate geometric scaling for the photon-proton cross section with a very simple saturation model. We describe the proton structure function F2 at small x in a wide kinematical range with an elementary functional form and a small number of free parameters. We speculate that the symmetry between low and high Q2 recently discovered in the data could be related to a well-known symmetry of the two-gluon- exchange dipole-dipole cross section.Comment: 15 pages, 4 figure

Features of personal profile in MMPI males with experience of primary samples of psychoactive substances

Background. The increase in drug use in the population of Russia and representatives of the youth in particular is a vital issue that is controlled and monitored by the federal state. The rapid rise in drug use in young citizens requires a systematic analysis of the causes, study of criteria and assessment of predisposition for drug use, and also the development of programs to prevent drug addiction in adolescents. Objective. Determination of the psychological predisposition of young men to psychoactive substances using the personality profile of the Multidisciplinary Method of Personality Inventory (MMPI). Research Progress. The research was conducted between 2008 and 2010 on the basis of secondary comprehensive schools, cadet corps, secondary professional educational institutions and universities in Rostov-on-Don and the Rostov region, Russia. The sample included 338 males from 15-16 to 22-23 years old, whose average age is 17-18 years. The evaluation of information reported by applicants on the fact of presence / absence of psychoactive substance samples was made based on the results of the psychophysiological test using a polygraph.Research Results. The results of the MMPI test were statistically analyzed according to the nonparametric MannWhitney test, and to a single-factor analysis of variance. The research results show that the scores of the F-scale in the MMPI profile of young males who used psychoactive substances reveal a statistically significant increase (p = 0.008), compared to those who did not use psychoactive substances. The single-factor analysis of the F- MMPI scale did not show a statistically significant difference (p = 0.128). Conclusion. The paper proposes to consider an increase in the F-scale in the MMPI profile as an indicator of individual predisposition to use psychoactive substances, but not to consider an increase in its indices as a cause that affects primary psychoactive substances in adolescence. The results obtained can be used by practical and clinical psychologists when working with adolescents and youths

Diffractive gauge bosons production beyond QCD factorisation

We discuss single diffractive gauge bosons ($\gamma^*,\,W^{\pm},\,Z$) production in proton-proton collisions at different (LHC and RHIC) energies within the color dipole approach. The calculations are performed for gauge bosons produced at forward rapidities. The diffractive cross section is predicted as function of fractional momentum and invariant mass of the lepton pair. We found a dramatic breakdown of the diffractive QCD factorisation caused by an interplay of hard and soft interactions. Data from the CDF experiment on diffractive production of $W$ and $Z$ are well explained in a parameter free way.Comment: 28 pages, 10 figures; a clarification of absorptive corrections has been added, typos corrected; the published versio