\mathcal{O}(\alpha ^2 L^2 ) radiative corrections to deep inelasticep scattering for different kinematical variables

The QED radiative corrections are calculated in the leading log approximation up to $\mathcal{O}(\alpha ^2 )$ for different definitions of the kinematical variables using jet measurement, the ‘mixed’ variables, the double angle method, and a measurement based onθ _e andy _JB . Higher order contributions due to exponentiation of soft radiation are included.     

Factorizable electroweak \mathcal{O}(\alpha) corrections for top quark pair production and decay at a linear e^+e^- collider

We calculate the standard model predictions for top quark pair production and decay into six fermions at a linear e⁺e^- collider. We include the factorizable electroweak $\mathcal{O}(\alpha)$ corrections in the pole approximation and QED corrections due to the initial state radiation in the structure function approach. The effects of the radiative corrections on the predictions are illustrated by showing numerical results for two selected six-fermion reactions $e^+e^-\rightarrow b\nu_{\mu}\mu^+\bar{b}\mu^-\bar{\nu}_\mu$ and $e^+e^-\rightarrow b\nu_{\mu}\mu^+\bar{b}d\bar{u}$ .     

Deep inelastic scattering with tagged initial state radiation: Complete \mathcal{O}(\alpha) leptonic QED corrections

In this paper we extend the calculation of the QED corrections to deep inelastic lepton-proton scattering with a tagged photon, taking into account the full corrections on the lepton side. Comparing to previous results that were obtained by considering only large logarithmic terms at leading and next-to-leading accuray, we find that the difference is in general quite small, however, it may be significant in the region of large y and small x. Received: 10 October 2001 / Published online: 14 December 2001     

Diphoton plus Z production at the ILC at \mathcal{O}(\alpha ^4)

In this paper, we consider a system of gravitating bodies in Kaluza–Klein models with toroidal compactification of the extra dimensions. To simulate the astrophysical objects (e.g., our Sun and pulsars) with energy density much greater than the pressure, we assume that these bodies are pressureless in the external space, i.e., the space we inhabit. At the same time, they may have nonzero parameters $\omega _{({\bar{\alpha }} -3)} \, ({\bar{\alpha }} =4,\ldots , D)$ in the equations of state in the extra dimensions. We construct the Lagrange function of this many-body system for any value of $\Sigma =\sum _{{\bar{\alpha }}} \omega _{({\bar{\alpha }} -3)}$ . Moreover, the gravitational tests (PPN parameters, perihelion and periastron advances) require a negligible deviation from the latent soliton value $\Sigma =-(D-3)/2$ . However, the presence of pressure/tension in the internal space results necessarily in the smearing of the gravitating masses over the internal space and in the absence of KK modes. This looks very unnatural from the point of view of quantum physics.     

Lepton-hadron correlations to\mathcal{O}(\alpha _s^2 ) in (2+1) jet production at electron-proton colliders

We present one-loop corrected results on the four parity-conserving structure functions that describe deep inelastic (2+1)-jet production at high energy electron-proton colliders.Supported in part by the BMFT, FRG under contract 06MZ760     

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 189 GeV at LEP

Cross-sections and angular distributions for hadronic and lepton pair final states in collisions at a centre-of-mass energy near 189 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The results are used to measure the energy dependence of the electromagnetic coupling constant , and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a sneutrino in supersymmetric theories with R-parity violation. A search for the indirect effects of the gravitational interaction in extra dimensions on the and final states is also presented. Received: 9 July 1999 / Published online: 17 February 2000     

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 189-209 GeV at LEP

Cross-sections and angular distributions for hadronic and lepton-pair final states in e ⁺ e^- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant at LEP 2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the -Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.Received: 28 August 2003, Published online: 18 February 2004     

Heavy quark vacuum polarization: first two moments of the ${\mathcal{O}}(\alpha_s^3 n_f^2)$ contribution

The vacuum polarization due to a virtual heavy quark pair and specifically the coefficients of its Taylor expansion in the external momentum are closely related to moments of the cross section for quark-antiquark pair production in electron-positron annihilation. Relating measurement and theoretically calculated Taylor coefficients, an accurate value for charm- and bottom-quark mass can be derived, once corrections from perturbative QCD are sufficiently well under control. Up to three-loop order these have been evaluated previously. We now present a subset of four-loop contributions to the lowest two moments, namely those from diagrams which involve two internal loops from massive and massless fermions coupled to virtual gluons, hence of order . The calculation demonstrates the applicability of Laportas algorithm to four-loop vacuum diagrams with both massive and massless propagators and should be considered a first step towards the full evaluation of the order contribution.Received: 22 December 2004, Published online: 3 March 2005K.G. Chetyrkin: On leave from Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, 117312, Russia.     

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 130–172 GeV at LEP

Production of events with hadronic and leptonic final states has been measured in collisions at centre-of-mass energies of 130–172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z events, and compared to Standard Model expectations. The ratio of the cross-section for production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of -Z interference. The energy dependence of has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for -channel contributions from new massive particles and to place limits on gaugino pair production with subsequent decay of the gaugino into a light gluino and a quark pair. Received: 30 July 1997 / Published online: 10 March 1998     

A new study of 25Mg(\alpha,n) 28Si angular distributions at E_{\alpha} =3-5 MeV

Heavy neutron-rich nuclei close to N = 126 were produced by fragmentation of a 1A GeV ²⁰⁸Pb beam at the FRS at GSI. The β-decay half-lives of 7 nuclides have been determined using a novel numerical analysis method. The half-lives of ^202,199Ir, ^200,199Os and ¹⁹⁶Re are reported for the first time. The comparison of the data with model calculations provides indications on the importance of first-forbidden transitions on the β-decay of nuclei around N = 126 and Z < 82.     

Measurement of the hadronic photon structure function $F_2^\gamma(x,Q^2)$ in two-photon collisions at LEP

The hadronic photon structure function is measured from data taken with the ALEPH detector at LEP. At centre-of-mass energies between and an integrated luminosity of is analyzed in two ranges of Q² with GeV² and 67.2 GeV². Detector effects and acceptance are corrected for with a Tikhonov unfolding procedure. The results are compared to theoretical predictions and measurements from other experiments.Received: 12 June 2003, Published online: 11 August 2003