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

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

Nonperturbative contributions to the quark form factor at high energy

The analysis of nonperturbative effects in high energy asymptotics of the electomagnetic quark form factor is presented. It is shown that the nonperturbative effects determine the initial value for the perturbative evolution of the quark form factor and find their general structure with respect to the high energy asymptotics. Within the Wilson integral formalism which is natural for investigation of the soft, IR sensitive, part of the factorized form factor, the structure of the instanton induced effects in the evolution equation is discussed. It is demonstrated that the instanton contributions result in the finite renormalization of the subleading perturbative result and numerically are characterized by small factor reflecting the diluteness of the QCD vacuum within the instanton liquid model. The relevance of the IR renormalon induced effects in high energy asymptotic behaviour is discussed. The consequences of the various analytization procedures of the strong coupling constant in the IR domain are considered.Comment: REVTeX, 12 pages, 1 figure. Important references and discussions added, misprints corrected, minor changes in tex

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

Matching NLO parton shower matrix element with exact phase space: case of W -> l nu (gamma) and gamma^* -> pi^+pi^-(gamma)

The PHOTOS Monte Carlo is often used for simulation of QED effects in decay of intermediate particles and resonances. Momenta are generated in such a way that samples of events cover the whole bremsstrahlung phase space. With the help of selection cuts, experimental acceptance can be then taken into account. The program is based on an exact multiphoton phase space. Crude matrix element is obtained by iteration of a universal multidimensional kernel. It ensures exact distribution in the soft photon region. Algorithm is compatible with exclusive exponentiation. To evaluate the program's precision, it is necessary to control the kernel with the help of perturbative results. If available, kernel is constructed from the exact first order matrix element. This ensures that all terms necessary for non-leading logarithms are taken into account. In the present paper we will focus on the W -> l nu and gamma^* -> pi^+ pi^- decays. The Born level cross sections for both processes approach zero in some points of the phase space. A process dependent compensating weight is constructed to incorporate the exact matrix element, but is recommended for use in tests only. In the hard photon region, where scalar QED is not expected to be reliable, the compensating weight for gamma^* decay can be large. With respect to the total rate, the effect remains at the permille level. It is nonetheless of interest. The terms leading to the effect are analogous to some terms appearing in QCD. The present paper can be understood either as a contribution to discussion on how to match two collinear emission chains resulting from charged sources in a way compatible with the exact and complete phase space, exclusive exponentiation and the first order matrix element of QED (scalar QED), or as the practical study of predictions for accelerator experiments.Comment: 24 page

The heat capacity of nitrogen chains in grooves of single-walled carbon nanotube bundles

The heat capacity of bundles of closed-cap single-walled carbon nanotubes (SWNT) with one-dimensional chains of nitrogen molecules adsorbed in the grooves has been first experimentally studied at temperatures from 2K to 40K using an adiabatic calorimeter. The contribution of nitrogen C(T) to the total heat capacity has been separated. In the region 2-8K the behaviour of the curve C(T) is qualitatively similar to the theoretical prediction of the phonon heat capacity of 1D chains of krypton (Kr) atoms localized in the grooves of SWNT bundles. Below 3K the dependence C(T) is linear. Above 8K the dependence C(T) becomes steeper in comparison with the case of Kr atoms. This behaviour of the heat capacity C(T) is due to the contribution of the rotational degrees of freedom of the nitrogen molecules.Comment: 15 pages, 4 figure

Features of modern electronic trading in international financial markets

The subject of research is the Internet trading in the American and European financial markets for individuals from the Russian Federation. The relevance of the topic is due to the huge influx of Russian private investors into the global financial market over the past few years, caused by the simplification of the process of opening brokerage accounts, automation of taxation, the possibility of trading via web terminals, as well as significantly changed conditions of online trading in 2022. The whole work is the development of a report on investing in the financial markets of the United States of America and the European Union for citizens of the Russian Federation. The study was conducted using the methods of systematization, grouping and comparison, with their help, analysis and generalization of the results obtained were carried out, conclusions were drawn. It has been established that in the current geopolitical situation and the restrictive measures taken by many multinational banks and companies, private investors of Russian origin have risks of freezing their own assets on brokerage accounts, which can be reduced by opening a brokerage account in companies registered in the territory of countries friendly to the Russian Federation. The article suggests two least risky options for investing in securities of issuers from Europe and USA