Radiative corrections to the background of μ→eγ\mu\to e\gamma decay

Radiative muon decay in the kinematics similar to the neutrinoless decay $\mu\to e\gamma$ is considered. Radiative corrections due to 1-loop virtual photons and emission of additional soft or hard photons are taken into account. Analytical expressions and numerical estimations are presented.Comment: 11 pages, LaTeX, misprints in Eqs.(9,12,14) fixe

Helicity amplitudes for the small--angle process e^-e^{\pm}\to e^-\gamma\gamma + e^{\pm} with both photons along one direction and its cross channel

We study the small--angle double bremsstrahlung in $e^-e^\pm$ scattering for a jet kinematics where both photons move along the electron direction. This region gives the main contribution to the cross section. We present analytic expressions for all 64 amplitudes with arbitrary helicity states of the initial and final leptons and the produced photons convenient for analytic and numerical studies. The accuracy of the obtained amplitudes is given omitting only terms of the order of m^2/E_j^2, \theta_j^2 and \theta_j m/E_j. The helicity amplitudes for the cross channel \gamma e^\pm \to \gamma e^+e^- + e^\pm are given. Several limits for the helicity amplitudes of hard or soft final particles are considered.Comment: 20 pp, LaTeX, 7 EPS figs, uses elsart packag

Radiative large-angle Bhabha scattering in collinear kinematics

The process of large-angle high energy electron-positron scattering with emission of one hard photon almost collinear to one of the charged particles momenta is considered. The differential cross section with radiative corrections due to emission of virtual and soft real photons calculated to a power accuracy is presented. Emission of two hard photons and total expressions for radiative correction are given in leading logarithmical approximation. The latter are illustrated by numeric estimates. A relation of the results with structure function formalism is discussed.Comment: 19 pp, LaTeX, uses epsfig package, 3 eps figs. Some small changes, including more explanations, addition of references and correction of misprints. Final version Accepted for publication, will appear on nuclear Physics B, issue 563 (1,2), cover date of the issue 6 December 199

Non-perturbative momentum dependence of the coupling constant and hadronic models

Models of hadron structure are associated with a hadronic scale which allows by perturbative evolution to calculate observables in the deep inelastic region. The resolution of Dyson-Schwinger equations leads to the freezing of the QCD running coupling (effective charge) in the infrared, which is best understood as a dynamical generation of a gluon mass function, giving rise to a momentum dependence which is free from infrared divergences. We use this new development to understand why perturbative treatments are working reasonably well despite the smallness of the hadronic scale.Comment: Changes in Acknowledgments and PACS number

Perturbative QCD analysis of the Bjorken sum rule

We study the polarized Bjorken sum rule at low momentum transfer squared Q2<3GeV2 in the twist-two approximation and to the next-to-next-to-leading order accuracy