640 research outputs found
Functional methods in the theory of magnetoimpurity states of electrons in quantum wires
Functional methods are used to study magnetoimpurity states of electrons in
nanostructures. The Keldysh formalism is applied to these states. The theory is
illustrated using a quantum wire sample with impurity atoms capable of
localizing electrons in a magnetic field. The characteristics of
magnetoimpurity states of electrons in the wire are calculated using the model
of a Gaussian separable potential.Comment: 15 pages, 1 figur
Antiangular Ordering of Gluon Radiation in QCD Media
We investigate angular and energy distributions of medium-induced gluon
emission off a quark-antiquark antenna in the framework of perturbative QCD as
an attempt toward understanding, from first principles, jet evolution inside
the quark-gluon plasma. In-medium color coherence between emitters, neglected
in all previous calculations, leads to a novel mechanism of soft-gluon
radiation. The structure of the corresponding spectrum, in contrast with known
medium-induced radiation, retains some properties of the vacuum case; in
particular, it exhibits a soft divergency. However, as opposed to the vacuum,
the collinear singularity is regulated by the pair opening angle, leading to a
strict angular separation between vacuum and medium-induced radiation, denoted
as antiangular ordering. We comment on the possible consequences of this new
contribution for jet observables in heavy-ion collisions.Comment: 4 pages, 2 figures; v2. a number of minor improvements, figures
updated, accepted for publication in PR
Impurity states of electrons in quantum dots in external magnetic fields
The influence of isolated impurity atoms on the electron energy spectrum in a
parabolic quantum dot in quantizing magnetic field is studied. The impurity
potential is approximated by a Gaussian separable operator which allows one to
obtain the exact solution of the problem. We demonstrate that in the electron
energy spectrum there is a set of local levels which are split from the Landau
zone boundaries in the upward or downward direction depending on the impurity
type. We have calculated the local level positions, the wave functions of
electrons in bound states, and the residues of the electron scattering
amplitudes by impurity atoms at the poles.Comment: 8 pages, 2 figures, to be published in European Physical Journal
Electroweak 2 -> 2 amplitudes for electron-positron annihilation at TeV energies
The non-radiative scattering amplitudes for electron-positron annihilation
into quark and lepton pairs in the TeV energy range are calculated in the
double-logarithmic approximation. The expressions for the amplitudes are
obtained using infrared evolution equations with different cut-offs for virtual
photons and for W and Z bosons, and compared with previous results obtained
with an universal cut-off.Comment: Revtex4, 17 pages, 7 figures. Some minor changes made, more refs
adde
Asymptotic high energy behavior of the deeply virtual Compton scattering amplitude
We compute the deeply virtual Compton scattering (DVCS) amplitude for forward
and backward scattering in the asymptotic limit. Since this calculation does
not assume ordering of the transverse momenta, it includes important
logarithmic contributions that are beyond those summed by the DGLAP evolution.
These contributions lead to a power-like behavior for the forward DVCS
amplitude.Comment: Latex, 22 pages, 5 Figures; references enhanced; typos correcte
Factorization and infrared properties of non-perturbative contributions to DIS structure functions
In this paper we present a new derivation of the QCD factorization. We deduce
the k_T- and collinear factorizations for the DIS structure functions by
consecutive reductions of a more general theoretical construction. We begin by
studying the amplitude of the forward Compton scattering off a hadron target,
representing this amplitude as a set of convolutions of two blobs connected by
the simplest, two-parton intermediate states. Each blob in the convolutions can
contain both the perturbative and non-perturbative contributions. We formulate
conditions for separating the perturbative and non-perturbative contributions
and attributing them to the different blobs. After that the convolutions
correspond to the QCD factorization. Then we reduce this totally unintegrated
(basic) factorization first to the k_T- factorization and finally to the
collinear factorization. In order to yield a finite expression for the Compton
amplitude, the integration over the loop momentum in the basic factorization
must be free of both ultraviolet and infrared singularities. This obvious
mathematical requirement leads to theoretical restrictions on the
non-perturbative contributions (parton distributions) to the Compton amplitude
and the DIS structure functions related to the Compton amplitude through the
Optical theorem. In particular, our analysis excludes the use of the singular
factors x^{-a} (with a > 0) in the fits for the quark and gluon distributions
because such factors contradict to the integrability of the basic convolutions
for the Compton amplitude. This restriction is valid for all DIS structure
functions in the framework of both the k_T- factorization and the collinear
factorization if we attribute the perturbative contributions only to the upper
blob.Comment: 19 pages, 6 figure
“Red banditry” as a Socio-Political Phenomenon of the Early 1920s (based on Materials from the Northern Kuzbass)
The relevance of the study is due to the presence of conflicts in the social and civil spheres of life both in modern Russia and in the world. A historical excursion into the problem under consideration will help to identify the causes of the confrontation in social conflicts, to develop measures aimed at eliminating and overcoming them. The article discusses the issues associated with the emergence of red banditry in the northern part of the modern Kemerovo region after the end of the Civil War. New archival materials are being introduced into scientific circulation. The novelty of the study is that based on the analysis of the data, the conclusions of researchers involved in the history of red banditry in Siberia are corrected. The author dwells on the facts of the manifestation of red banditry in the Mariinsky district of Tomsk province, reveals the essence of this phenomenon. It is proved that the causes of this phenomenon, in addition to the negative reaction of the Soviet government to the Kolchak regime, the low level of political and spiritual culture of representatives of the new government, the strong influence of partisans, the emergence of a sense of impunity and permissiveness, included such reasons as personal contempt and hostility between ordinary residents, as well as basic desire to appropriate another's property
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