463 research outputs found
Weak localization of holes in high-mobility heterostructures
Theory of weak localization is developed for two-dimensional holes in
semiconductor heterostructures. Ballistic regime of weak localization where the
backscattering occurs from few impurities is studied with account for
anisotropic momentum scattering of holes. The transition from weak localization
to anti-localization is demonstrated for long dephasing times. For stronger
dephasing the conductivity correction is negative at all hole densities due to
non-monotonous dependence of the spin relaxation time on the hole wavevector.
The anomalous temperature dependent correction to the conductivity is
calculated. We show that the temperature dependence of the conductivity is
non-monotonous at moderate hole densities.Comment: 5 pages, 4 figure
Spin-orbit interaction and weak localization in heterostructures
Theory of weak localization in two-dimensional high-mobility semiconductor
systems is developed with allowance for the spin-orbit interaction. The
obtained expressions for anomalous magnetoresistance are valid in the whole
range of classically weak magnetic fields and for arbitrary strengths of bulk
and structural inversion asymmetry contributions to the spin splitting. The
theory serves for both diffusive and ballistic regimes of electron propagation
taking into account coherent backscattering and nonbackscattering processes.
The transition between weak localization and antilocalization regimes is
analyzed. The manifestation of the mutual compensation of Rashba and
Dresselhaus spin splittings in magnetoresistance is discussed. Perfect
description of experimental data on anomalous magnetoresistance in
high-mobility heterostructures is demonstrated. The in-plane magnetic field
dependence of the conductivity caused by an interplay of the spin-orbit
splittings and Zeeman effect is described theoretically.Comment: Review for the special issue of Semicond. Sci. Technol. "The effects
of spin-orbit interaction on charge transport". 8 pages, 5 figure
Pion-nucleon scattering in covariant baryon chiral perturbation theory with explicit Delta resonances
We present the results of a third order calculation of the pion-nucleon
scattering amplitude in a chiral effective field theory with pions, nucleons
and delta resonances as explicit degrees of freedom. We work in a manifestly
Lorentz invariant formulation of baryon chiral perturbation theory using
dimensional regularization and the extended on-mass-shell renormalization
scheme. In the delta resonance sector, the on mass-shell renormalization is
realized as a complex-mass scheme. By fitting the low-energy constants of the
effective Lagrangian to the - and -partial waves a satisfactory
description of the phase shifts from the analysis of the Roy-Steiner equations
is obtained. We predict the phase shifts for the and waves and compare
them with the results of the analysis of the George Washington University
group. The threshold parameters are calculated both in the delta-less and
delta-full cases. Based on the determined low-energy constants, we discuss the
pion-nucleon sigma term. Additionally, in order to determine the strangeness
content of the nucleon, we calculate the octet baryon masses in the presence of
decuplet resonances up to next-to-next-to-leading order in SU(3) baryon chiral
perturbation theory. The octet baryon sigma terms are predicted as a byproduct
of this calculation.Comment: 41 pages, 12 figures, 7 table
Tvorba eta mezona u nn sudarima
A model calculation for near-threshold η meson production in nucleon-nucleon collisions is presented. The η meson production is described by elementary rescattering processes via MN→ ηN, with M = π, ρ, η and σ. Corresponding amplitudes are taken from a multi-channel meson-exchange model of the πN system developed by the Jülich group. Effects of the NN interaction in the final as well as in the initial state are taken into account microscopically.Predstavljamo model za računanje tvorbe η mezona blizu praga u sudarima nukleon-nukleon. Tvorba η mezona opisuje se elementarnim procesima ponovnog raspršenja putem MN→ ηN, sa M = π, ρ, η i σ. Odnosne amplitude uzimaju se od višekanalnog modela izmjene mezona u sustavu πN koji je razvila grupa u Jülichu. Učinci međudjelovanja u konačnom stanju kao i u početnom stanju uzeti su u obzir mikroskopski
Extraction of scattering lengths from final-state interactions
A recently proposed method based on dispersion theory, that allows to extract
the scattering length of a hadronic two-body system from corresponding
final-state interactions, is generalized to the situation where the Coulomb
interaction is present. The steps required in a concrete practical application
are discussed in detail. In addition a thorough examination of the accuracy of
the proposed method is presented and a comparison is made with results achieved
with other methods like the Jost-function approach based on the effective-range
approximation. Deficiencies of the latter method are pointed out. The
reliability of the dispersion theory method for extracting also the effective
range is investigated.Comment: 16 pages, 6 figures, some corrections to text, to appear in Phys.
Rev.
Exclusive and semi-inclusive strangeness and charm production in and reactions
Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology
we consider the reactions and which are dominated by the contributions of the and
Regge trajectories, respectively. The spin structure of the amplitudes is
described by introducing Reggeized Born terms. It is found that the existing
data for the reaction are in reasonable agreement
with the model predictions. To describe the absolute values of the cross
sections it is necessary to introduce also suppression factors which can be
related to absorption corrections. Furthermore, assuming the SU(4) symmetry to
hold for Regge residues and the universality of absorption corrections we
calculate the cross section of the reaction .
Employing the latter results from reactions we then estimate the
contributions of the pion exchange mechanism to the cross sections of the
reactions and and compare them
with the contributions of the and exchanges. We find that the
reactions are dominated not by pion exchange but by and exchanges,
respectively. Moreover, assuming the SU(4) symmetry to hold approximately for
the coupling constants = we analyze also
the production of leading hyperons in the reaction . It is shown that the non-perturbative mechanism should give an
essential contribution to the yield for .Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002,
Juelich, June 10-14, 200
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