Gauge-Boson Production in Electron-Photon Collisions

We summarize results for the processes $e^-\gamma \to \nu W^-, e^-Z, e^-\gamma$ within the electroweak Standard Model. We discuss the essential features of the corresponding lowest-order cross-sections and present numerical results for the unpolarized cross-sections including the complete $O(\alpha)$ virtual, soft-photonic, and hard-photonic corrections. While at low energies the weak corrections are dominated by the leading universal corrections, at high energies we find large, non-universal corrections, which arise from vertex and box diagrams involving non-Abelian gauge couplings.Comment: 7 pages + 5 figures appended as ps-files (uuencoded), latex, CERN-TH. 6980/9

The Higgs Boson in the Standard Model - From LEP to LHC: Expectations, Searches, and Discovery of a Candidate

The quest for the Higgs boson of the Standard Model, which was a cornerstone in the physics programme at particle colliders operating at the energy frontier for several decades, is the subject of this review. After reviewing the formulation of electroweak symmetry breaking via the Higgs mechanism within the Standard Model, the phenomenology of the Higgs boson at colliders and the theoretical and phenomenological constraints on the Standard Model Higgs sector are discussed. General remarks on experimental searches and the methodology of statistical interpretation are followed by a description of the phenomenology of Higgs-boson production and the corresponding precise predictions. The strategies of the experimental searches and their findings are discussed for the Large Electron Positron Collider (LEP) at CERN, the proton-antiproton collider Tevatron at Fermilab, and the proton-proton Large Hadron Collider (LHC) at CERN. The article concludes with the description of the observation of a Higgs-like boson at the LHC.Comment: 82 pages, 34 figures, minor modifications, version equivalent to the one published in Prog. Part. Nucl. Phy

Approximations for W-Pair Production at Linear-Collider Energies

We determine the accuracy of various approximations to the O(alpha) corrections for on-shell W-pair production. While an approximation based on the universal corrections arising from initial-state radiation, from the running of alpha, and from corrections proportional to m_t^2 fails in the Linear-Collider energy range, a high-energy approximation improved by the exact universal corrections is sufficiently good above about 500GeV. These results indicate that in Monte Carlo event generators for off-shell W-pair production the incorporation of the universal corrections is not sufficient and more corrections should be included.Comment: 7 pages, late

Techniques for one-loop tensor integrals in many-particle processes

We briefly sketch the methods for a numerically stable evaluation of tensor one-loop integrals that have been used in the calculation of the complete electroweak one-loop corrections to \Pep\Pem\to4 fermions. In particular, the improvement of the new methods over the conventional Passarino--Veltman reduction is illustrated for some 4-point integrals in the delicate limits of small Gram (and other kinematical) determinants.Comment: 5 pages, latex, 2 postscript figures, to appear in the proceedings of the "7th International Symposium on Radiative Corrections (RADCOR2005)", Shonan Village, 200

Reduction schemes for one-loop tensor integrals

We present new methods for the evaluation of one-loop tensor integrals which have been used in the calculation of the complete electroweak one-loop corrections to e+ e- -> 4 fermions. The described methods for 3-point and 4-point integrals are, in particular, applicable in the case where the conventional Passarino-Veltman reduction breaks down owing to the appearance of Gram determinants in the denominator. One method consists of different variants for expanding tensor coefficients about limits of vanishing Gram determinants or other kinematical determinants, thereby reducing all tensor coefficients to the usual scalar integrals. In a second method a specific tensor coefficient with a logarithmic integrand is evaluated numerically, and the remaining coefficients as well as the standard scalar integral are algebraically derived from this coefficient. For 5-point tensor integrals, we give explicit formulas that reduce the corresponding tensor coefficients to coefficients of 4-point integrals with tensor rank reduced by one. Similar formulas are provided for 6-point functions, and the generalization to functions with more internal propagators is straightforward. All the presented methods are also applicable if infrared (soft or collinear) divergences are treated in dimensional regularization or if mass parameters (for unstable particles) become complex.Comment: 55 pages, latex, some references updated and few comments added, version to appear in Nucl. Phys.

Electroweak Radiative Corrections to Off-Shell W-Pair Production

We briefly describe the RacoonWW approach to calculate radiative corrections to e+ e- -> W W -> 4 fermions and present numerical results for the total W-pair production cross section at LEP2.Comment: 3 pages, 2 figures, talk given at the DPF2000 meeting, Columbus, OH, August 9-12, 200

Z+jet production at the LHC: Electroweak radiative corrections

The investigation of weak bosons $V$ ($V=\mathrm{W}^{\pm}$, $\mathrm{Z}$) produced with or without associated hard QCD jets will be of great phenomenological interest at the LHC. Owing to the large cross sections and the clean decay signatures of the vector bosons, weak-boson production can be used to monitor and calibrate the luminosity of the collider, to constrain the PDFs, or to calibrate the detector. Moreover, the $Z$+jet(s) final state constitutes an important background to a large variety of signatures of physics beyond the Standard Model. To match the excellent experimental accuracy that is expected at the LHC, we have worked out a theoretical next-to-leading-order analysis of $V$+jet production at hadron colliders. The focus of this talk will be on new results on the full electroweak corrections to $Z(\to l^-l^+)$+jet production at the LHC. All off-shell effects are included in our approach, and the finite lifetime of the $Z$ boson is consistently accounted for using the complex-mass scheme. In the following, we briefly introduce the calculation and discuss selected phenomenological implications of our results.Comment: 5 pages, 2 figures, talk at the "35th International Conference on High Energy Physics", Paris, France, July 22 -- 28, 201

Probing anomalous quartic gauge-boson couplings via e+e- --> 4fermions+gamma

All lowest-order amplitudes for e+e- --> 4f+gamma are calculated including five anomalous quartic gauge-boson couplings that are allowed by electromagnetic gauge invariance and the custodial SU(2)_c symmetry. Three of these anomalous couplings correspond to the operators L_0, L_c, and L_n that have been constrained by the LEP collaborations in WWgamma production. The anomalous couplings are incorporated in the Monte Carlo generator RACOONWW. Moreover, for the processes e+e- --> 4f+gamma RACOONWW is improved upon including leading universal electroweak corrections such as initial-state radiation. The discussion of numerical results illustrates the size of the leading corrections as well as the impact of the anomalous quartic couplings for LEP2 energies and at 500GeV.Comment: 27 pages, latex, 42 postscript files, some misprints correcte