One-loop leading logarithms in electroweak radiative corrections

We discuss the evaluation of the collinear single-logarithmic contributions to virtual electroweak corrections at high energies. More precisely, we prove the factorization of the mass singularities originating from loop diagrams involving collinear virtual gauge bosons coupled to external legs. We discuss, in particular, processes involving external longitudinal gauge bosons, which are treated using the Goldstone-boson equivalence theorem. The proof of factorization is performed within the 't Hooft–Feynman gauge at one-loop order and applies to arbitrary electroweak processes that are not mass-suppressed at high energies. As basic ingredients we use Ward identities for Green functions with arbitrary external particles involving a gauge boson collinear to one of these. The Ward identities are derived from the BRS invariance of the spontaneously broken electroweak gauge theory. Received: 4 May 2001 / Published online: 6 July 2001     

One-loop leading logarithms in electroweak radiative corrections

We present results for the complete one-loop electroweak logarithmic corrections for general processes at high energies and fixed angles. Our results are applicable to arbitrary matrix elements that are not mass suppressed. We give explicit results for 4-fermion processes and gauge-boson pair production in annihilation. Received: 20 October 2000 / Published online: 23 January 2001     

Enhanced electroweak radiative corrections in SUSY: Gluon-free observables

The large top-quark mass is responsible for the enhancement of the oblique radiative corrections in SUSY models. We present analytical formulas for these corrections to the W-boson mass m _W and to the Z l ⁺ l ⁻-coupling constants. A comparison with the result of the standard model fit is made. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 723–726 (25 May 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Two photon QED corrections in helium like highly charged ions

An overview of calculations and measurements of the energy levels of helium-like ions is presented. We focus on the two-photon QED effects, and conclude that measurements of the excited states of large Z helium-like ions are desired. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enhanced electroweak radiative corrections in SUSY and precision data

Enhanced radiative corrections generated in SUSY extensions of the Standard Model spoil the fit of the precision data (Z-boson decay parameters and W-boson mass). This negative effect is washed out for heavy enough squarks, because of the decoupling property of SUSY models. We find that even for light squarks the enhanced radiative corrections can be small. In this case substantial mixing is necessary.     

The radiative corrections to the electroweak parameters in the dominant fermion-loop approximation

A simple treatment of the dominant radiative corrections to theW ^± andZ ⁰ mass formulae due to fermion-loop corrections to the propagator is given, including the possibility of a very massive top quark,m _t >M _w . A thorough comparison with the results of the complete (SU(2) _L ×U(1) _Y ) one-loop calculations is presented. Using α,G _μ andM _z as input, we find excellent agreement with the complete one-loop calculations (withm _HIGGS?100GeV) for all values ofm _t within an expected error ofΔM _W ?(α/2πM _W ?100MeV) inM _W andΔs _W ² ?0.002 in the weak angle,s _w ² . Technically we differ from previous work in diagonalizing the γZ propagator for arbitrary values ofq ², thus allowing for extensive use of the notion of “running” coupling constants and masses. We also give a simple and closed formula for the radiative corrections to be applied tos _w ² (accurate within an expected error ofΔs _w ² ?0.002), when extractings _W ² ?0.002), when extractings _W ² from neutrino scattering experiments. As a strategy for future precision tests of the electroweak theory, we suggest attempting to isolate and to test directly the “new physics” of boson loops and other new phenomena by comparing with and looking for deviations (larger thanΔM _W ?(α/2π)M _w ) from the predictions of the dominant fermion-loop calculation.     

高离化态金离子的辐射复合及其退激发过程的理论研究

利用基于多组态Dirac-Fock方法的程序包GRASP92和RATIP以及最新发展的RERR06程序,详细计算了高离化态金离子(类镍Au51+、类铜Au50+和类锌Au49+)俘获一个自由电子到nl(n=4—8,l=0—3)壳层的辐射复合谱以及相应的辐射退激发谱.理论计算的辐射复合谱很好地重现了实验谱.研究结果表明:对类镍Au51+、类铜Au50+和类锌Au49+而言,将一个自由电子俘获到n=4壳层的概率最大;在辐射复合过程之后,处在n=4壳层的俘获电子的辐射退激发谱线最强,并且体现了整个辐射退激发谱的主要特征.     

Evidence for strong Breit interaction in dielectronic recombination of highly charged heavy ions

Resonant strengths have been measured for dielectronic recombination of Li-like iodine, holmium, and bismuth using an electron beam ion trap. By observing the atomic number dependence of the state-resolved resonant strength, clear experimental evidence has been obtained that the importance of the generalized Breit interaction (GBI) effect on dielectronic recombination increases as the atomic number increases. In particular, it has been shown that the GBI effect is exceptionally strong for the recombination through the resonant state [1s2s(2)2p(1/2)](1).     

Full electroweak one-loop radiative corrections to squark decays in the MSSM

We present results on the full one-loop electroweak radiative corrections to the squark decay partial widths into charginos and neutralinos. We show the renormalization framework, and present numerical results for the third squark family. The corrections can reach values of 10%, which are comparable to the radiative corrections from the strong sector of the model. Therefore they should be taken into account for the precise extraction of the SUSY parameters at future colliders.     

Radiative and interelectronic-interaction corrections to the hyperfine splitting in highly charged B-like ions

The ground-state hyperfine splitting values of high-Z boronlike ions are calculated. Calculation of the interelectronic-interaction contribution is based on a combination of the 1/Z perturbation theory and the large-scale configuration-interaction Dirac-Fock-Sturm method. The screened QED corrections are evaluated utilizing an effective screening potential approach. Total hyperfine splitting energies are presented for several B-like ions of particular interest: ⁴⁵Sc¹⁶⁺, ⁵⁷Fe²¹⁺, ²⁰⁷Pb⁷⁷⁺, and ²⁰⁹Bi⁷⁸⁺. For lead and bismuth the experimental values of the 1s hyperfine splitting are employed to improve significantly the theoretical results by reducing the uncertainty due to the nuclear effects.     

Calculation of photon angular distribution and polarization for radiative recombination for highly charged helium-like ions

A systematic study is carried out on the angular distribution and polarization of photons emitted following radiative recombination of He-like ions by a non-relativistic dipole approximation. In order to incorporate the screening effect due to inner-shell electrons, a distorted wave approach is used. The dependence of the calculated angular distribution and polarization on the reduced-energy and nuclear charge are fitted by the corresponding empirical formulas, respectively.     

Estimate of the second order electron self energy corrections in highly charged heavy ions

An estimate for the last unknown gauge-invariant set of QED corrections of order α², the second-order self-energy correction, is presented utilizing the so-called sign approximation. This is able to reduce the present uncertainties in Lamb-shift predictions considerably. This revised version was published online in August 2006 with corrections to the Cover Date.     

The spectral lines of highly charged gold ions

Extreme ultraviolet spectra of highly charged gold were produced with an electron beam ion trap at the University of Electro-Communications, Tokyo. The X-ray spectra (3240–3360?eV) of Au with well-defined maximum charge states ranging from Cu- to Se-like ions were recorded. Guided by configuration interaction calculations, the strongest 3d–5f transitions have been well defined.     

Laser spectroscopy for QED tests in highly charged ions

An overview on laser spectroscopic work on highly charged ions (HCI) currently performed or in preparation at GSI is given. This includes laser spectroscopy on HCI in ion traps at the HITRAP facility and at the experimental storage ring (ESR).     

Uncertainties in τ polarization measurement at SLC/LEP and QED/electroweak radiative corrections

We discuss the τ polarization measurement at SLC/LEP energies as a data point in the precision tests of the Glashow-Salam-Weinberg model. Theoretical and experimental uncertainties of this measurement are examined and it is concluded that apart from left-right asymmetry measurement, and for typical values of the parameters of the Standard Model, the τ polarization offers the best probe of the couplings of leptons to the Z⁰. In particular, the dependence of the τ polarization on the top and Higgs masses is discussed. The interplay of QED initial state bremsstrahlung and other classes of radiative corrections is also discussed.     

Standard SANC modules for NLO QCD radiative corrections to single top-quark production

In this paper we present the results obtained with the newly created standard SANC modules for calculation of the NLO QCD corrections to single top-quark-production processes in s and t channels at the partonic level, as well as to top-decays. The main aim of these results is to prove the correct work of modules. A comprehensive comparison with the results of the CompHEP system is given, where possible. These modules are intended to be used in Monte Carlo generators for single top-quark-production processes at the LHC. As in our recent paper, devoted to the electroweak corrections to these processes, we study the regularization of the top-legs associated infrared divergences with the aid of the complex mass of the top quark. A comparison of QCD corrections with those computed by the conventional method is presented both for top production and for decays. For s-channel production we give an analytic proof of equivalence of the two methods in the limit of low top width.