Radiative corrections to positronium energy levels

A systematic perturbation theory for the computation of positronium energy levels is presented. The proposed method is based on the Bethe-Salpeter equation and a zeroth-order kernel for which exact solutions are known explicitly. The cancellation of ultraviolet divergences arising in the perturbation series is discussed, and new contributions to the ground-state hyperfine splitting of positronium are evaluated up to order α⁶.     

Radiative corrections to parapositronium decay

Radiative corrections to the two-gamma decay of parapositronium are examined. Special care is taken in the handling of the so-called binding diagram; in particular, the limiting procedure related to the infrared divergence is considered carefully. The general covariant gauges and the Fried-Yennie gauge are used in the computation to see that gauge invariance is accounted for. The order α correction of Harris and Brown is confirmed. In addition, from a sharp peak of the matrix element at low momentum and the low-momentum correction to the wave function, an α² ln α^?1 correction is derived.     

Radiative corrections to the light muonic atoms decay rate

Radiative corrections to the decay rate in low-Z hydrogen-like muonic atoms are considered. The correction is due to the Uehling potential and it has the relative order of α. The numerical results are reported for the 2p → 1s transition for atoms with nuclear charge up to Z = 10.     

New theory of positronium decay and relativistic wave function corrections

The positronium decay rate is calculated directly from the scattering amplitude by analytic continuation to the bound-state singularities. Relativistic wave function corrections are obtained which improve the agreement between theory and experiment.     

Electron polarization in polarized muon decay: Radiative corrections

We calculate the first-order radiative corrections to the decay spectrum of polarized muons, for the case where the electron polarization is also observed. The significance of the results for further studies on muon decay is discussed.     

Radiative corrections to the decay H^+ \to W^+ A^0

Full one-loop electroweak corrections to the on-shell decay are computed in the framework of models with two Higgs doublets (THDM). Such a decay may be dominant for over a wide range of parameter space relevant at present and future colliders. We show that the corrections may approach 40% and in particular are sensitive to , which parameterizes the discrete symmetry breaking term. We suggest that a measurement of the branching ratio of may offer a possibility of measuring the magnitude of . Received:17 July 2000 / Revised version: 28 February 2001 / Published online: 3 May 2001     

Radiative corrections to muon decay in leading and next-to-leading approximation for electron spectrum

We have noted that the electron spectrum of muon decay in the leading logarithmic approximation calculated in two lowest orders of the perturbation theory in the paper of Berman (1958), can be reproduced by the parton language. This fact permits one to generalize the result to all orders of the perturbation theory using the structure function method.     

Radiative corrections to muon and beta decay in the intermediate Vector Boson theory

The radiative corrections to muon and beta decay are examined in detail using the ξ-limiting formalism ofLee andYang. The electron spectra for both decays are calculated. It is found that the muon lifetime discrepancy is reduced considerably if one considers, quantitatively, the effect of strong interactions on the weak vector coupling constant as determined from the neutron's lifetime.     

Radiative corrections to pion-nucleus bremsstrahlung

We calculate the one-photon loop radiative corrections to virtual pion Compton scattering → , that subprocess which determines in the one-photon exchange approximation the pion-nucleus bremsstrahlung reaction Z → Z . Ultraviolet and infrared divergencies of the loop integrals are both treated by dimensional regularization. Analytical expressions for the O() corrections to the virtual Compton scattering amplitudes, A(s, u, Q) and B(s, u, Q) , are derived with their full dependence on the (small) photon virtuality Q from 9 classes of contributing one-loop diagrams. Infrared finiteness of these virtual radiative corrections is achieved (in the standard way) by including soft photon radiation below an energy cut-off . In the region of low center-of-mass energies, where the pion-nucleus bremsstrahlung process is used to extract the pion electric and magnetic polarizabilities, we find radiative corrections up to about -3% for = 5 MeV. Furthermore, we extend our calculation of the radiative corrections to virtual pion Compton scattering → by including the leading pion-structure effect in the form of the polarizability difference - . Our analytical results are particularly relevant for analyzing the data of the COMPASS experiment at CERN which aims at measuring the pion electric and magnetic polarizabilities with high statistics using the Primakoff effect.     

Radiative corrections to a non-linear oscillator

A theoretical and experimental investigation of the processes by which thin layers of gas trapped between surfaces of a structure may contribute to damping of structural vibrations is described. Effects of gas compressibility, inertia and thermal conductivity are allowed for in the theory. Particular attention is given to the variation of damping with gas pressure and layer thickness. The aim of the investigation was to provide results of use in the design of vibration absorbers for use in pressurized gas environments, as well as to contribute to a better understanding of the behaviour of pre-existing gas layers in structures.     

Radiative corrections to the Bhabha scattering

In this review we consider the high energy processes in QED frames in peripherical kinematics. The key feature of this kinematics is that processes have a large cross section which do not decrease with the increasing of the initial center of mass energy. Two purposes to study peripheral processes are: the background processes with large total cross sections and the structure of jets in the fragmentation region.     

Radiative corrections to high-energy neutrino scattering

Motivated by precise neutrino experiments, we reconsider the electromagnetic radiative corrections to the data. We investigate the usefulness and demonstrate the simplicity of the “leading log” approximation: the calculation to order α ln (Q/μ), α ln (Q/m_q). Here Q is an energy scale of the overall process, μ is the lepton mass and m_q is a hadronic mass, the effective quark mass in a parton model. We identify those questions the answers to which do not depend on unknown hadron parameters like quark masses. The leading log radiative corrections to dδ/dy distributions and to suitably interpreted dδ/dx distributions are quark-mass independent. We improve upon the conventional leading log approximation and compute explicitly the largest terms that lie beyond the leading log level. In practice this means that our model-independent formulae, though approximate, are likely to be excellent estimates everywhere except at low energy or very large y. We point out that radiative corrections to measurements of deviations from the Callan-Gross relation and to measurements of the “sea” constituency of nucleons are gigantic. The QCD inspired study of deviations from scaling is of particular interest. We compute, beyond the leading log level, the radiative corrections to the QCD predictions.     

Radiative corrections to pseudoscalar meson decays

Recoupling matrix elements are evaluated in the harmonic oscillator approximation for all possible angular and radial excitations in processes where quarks recombine. A diagrammatic representation is given. Their use is demonstrated in calculating the transition potential for ρ→2π in a pair creation model.     

Radiative corrections to neutral pion-pair production

We calculate the one-photon loop radiative corrections to the neutral pion-pair photoproduction process p^-g ?p^-p⁰p⁰\pi^-\gamma \ensuremath \rightarrow\pi^-\pi^0\pi^0 . At leading order this reaction is governed by the chiral pion-pion interaction. Since the chiral p⁺ \pi^{+}_{} p^- \pi^{-}_{} ? \rightarrow p⁰ \pi^{0}_{} p⁰ \pi^{0}_{} contact vertex depends only on the final-state invariant mass it factors out of all photon loop diagrams. We give analytical expressions for the multiplicative correction factor R ~ a/2p\ensuremath R\sim \alpha/2\pi arising from eight classes of contributing one-photon loop diagrams. An electromagnetic counterterm has to be included in order to cancel the ultraviolet divergences generated by the photon loops. Infrared finiteness of the virtual radiative corrections is achieved (in the standard way) by including soft photon radiation below an energy cut-off l \lambda . The radiative corrections to the total cross-section vary between +2% and -2% for center-of-mass energies from threshold up to 7m_p\ensuremath 7m_{\pi} . We study also the radiative corrections to the p⁰p⁰\ensuremath \pi^0\pi^0 mass spectrum.