104 research outputs found
Four-dimensional integration by parts with differential renormalization as a method of evaluation of Feynman diagrams
It is shown how strictly four-dimensional integration by parts combined with
differential renormalization and its infrared analogue can be applied for
calculation of Feynman diagrams.Comment: 6 pages, late
Non-Linear Algebra and Bogolubov's Recursion
Numerous examples are given of application of Bogolubov's forest formula to
iterative solutions of various non-linear equations: one and the same formula
describes everything, from ordinary quadratic equation to renormalization in
quantum field theory.Comment: LaTex, 21 page
A transverse current rectification in graphene superlattice
A model for energy spectrum of superlattice on the base of graphene placed on
the striped dielectric substrate is proposed. A direct current component which
appears in that structure perpendicularly to pulling electric field under the
influence of elliptically polarized electromagnetic wave was derived. A
transverse current density dependence on pulling field magnitude and on
magnitude of component of elliptically polarized wave directed along the axis
of a superlattice is analyzed.Comment: 12 pages, 6 figure
Structural Insight into Archaic and Alternative Chaperone-Usher Pathways Reveals a Novel Mechanism of Pilus Biogenesis
AVZ is supported by the Finnish Academy (grants 140959 and 273075; http://sciencenordic.com/partner/academy-finland) and Sigrid Juselius Foundation (grant 2014; www.sigridjuselius.fi/foundation). SMis supported by the Wellcome Trust (Senior Investigator Award 100280, Programme grant 079819; http://www.wellcome.ac.uk) The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Generalized Quark Transversity Distribution of the Pion in Chiral Quark Models
The transversity generalized parton distributions (tGPDs) of the the pion,
involving matrix elements of the tensor bilocal quark current, are analyzed in
chiral quark models. We apply the nonlocal chiral models involving a
momentum-dependent quark mass, as well as the local Nambu--Jona-Lasinio with
the Pauli-Villars regularization to calculate the pion tGPDs, as well as
related quantities following from restrained kinematics, evaluation of moments,
or taking the Fourier-Bessel transforms to the impact-parameter space. The
obtained distributions satisfy the formal requirements, such as proper support
and polynomiality, following from Lorentz covariance. We carry out the
leading-order QCD evolution from the low quark-model scale to higher lattice
scales, applying the method of Kivel and Mankiewicz. We evaluate several
lowest-order generalized transversity form factors, accessible from the recent
lattice QCD calculations. These form factors, after evolution, agree properly
with the lattice data, in support of the fact that the spontaneously broken
chiral symmetry is the key element also in the evaluation of the transversity
observables.Comment: 17 pages, 17 figures, regular pape
Initial Conditions for Semiclassical Field Theory
Semiclassical approximation based on extracting a c-number classical
component from quantum field is widely used in the quantum field theory.
Semiclassical states are considered then as Gaussian wave packets in the
functional Schrodinger representation and as Gaussian vectors in the Fock
representation. We consider the problem of divergences and renormalization in
the semiclassical field theory in the Hamiltonian formulation. Although
divergences in quantum field theory are usually associated with loop Feynman
graphs, divergences in the Hamiltonian approach may arise even at the tree
level. For example, formally calculated probability of pair creation in the
leading order of the semiclassical expansion may be divergent. This observation
was interpretted as an argumentation for considering non-unitary evolution
transformations, as well as non-equivalent representations of canonical
commutation relations at different time moments. However, we show that this
difficulty can be overcomed without the assumption about non-unitary evolution.
We consider first the Schrodinger equation for the regularized field theory
with ultraviolet and infrared cutoffs. We study the problem of making a limit
to the local theory. To consider such a limit, one should impose not only the
requirement on the counterterms entering to the quantum Hamiltonian but also
the requirement on the initial state in the theory with cutoffs. We find such a
requirement in the leading order of the semiclassical expansion and show that
it is invariant under time evolution. This requirement is also presented as a
condition on the quadratic form entering to the Gaussian state.Comment: 20 pages, Plain TeX, one postscript figur
Nonforward Parton Distributions
Applications of perturbative QCD to deeply virtual Compton scattering and
hard exclusive electroproduction processes require a generalization of usual
parton distributions for the case when long-distance information is accumulated
in nonforward matrix elements of quark and gluon light-cone operators.
We describe two types of nonperturbative functions parametrizing such matrix
elements: double distributions F(x,y;t) and nonforward distribution functions
F_\zeta (X;t), discuss their spectral properties, evolution equations which
they satisfy, basic uses and general aspects of factorization for hard
exclusive processes.Comment: Final version, to be published in Phys.Rev.
Feynman graph polynomials
The integrand of any multi-loop integral is characterised after Feynman
parametrisation by two polynomials. In this review we summarise the properties
of these polynomials. Topics covered in this article include among others:
Spanning trees and spanning forests, the all-minors matrix-tree theorem,
recursion relations due to contraction and deletion of edges, Dodgson's
identity and matroids.Comment: 35 pages, references adde
СИСТЕМА ОХРАНЫ ТРУДА И ПРОФЕССИОНАЛЬНЫЕ РИСКИ
The modernization of the safety and labor protection system within Russian Railways is based on some new approaches, including the professional risks management. The article analyzes the results of a pilot project of professional risk management system implemented within the Oktiabrskaya direction of track repairs.Идущая в сети российских железных дорог модернизация системы безопасности и охраны труда основана на ряде новых подходов. Одним из них стало управление профессиональными рисками. Статья посвящена анализу результатов реализации риск- менеджмента в рамках пилотного проекта на полигоне Октябрьской дирекции по ремонту пути, входящей в холдинговую структуру ОАО «РЖД».
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