Top quark signatures of Higgsless models

In these proceedings I describe the use of tree level unitarity to constrain top quark signatures of Higgsless electroweak models and discuss implications for collider phenomenology.Comment: 5 pages, 3 figures, aipproc style. To appear in the proceedings of SUSY06, 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, UC Irvine, California, USA 12-17 June 200

Effective Theory Approach to W-Pair Production near Threshold

In this talk, I review the effective theory approach to unstable particle production and present results of a calculation of the process e- e+ ->mu- nubar_mu u dbar X near the W-pair production threshold up to next-to-leading order in GammaW/MW ~ alpha ~ v^2. The remaining theoretical uncertainty and the impact on the measurement of the W mass is discussed.Comment: 7 pages (ilcws07.cls included), to appear in the proceedings of the International Linear Collider Workshop (LCWS/ILC07), 30 May - 3 Jun 2007, Hamburg, German

Soft-gluon and Coulomb corrections to hadronic top-quark pair production beyond NNLO

We construct a resummation at partial next-to-next-to-next-to-leading logarithmic accuracy for hadronic top-quark pair production near partonic threshold, including simultaneously soft-gluon and Coulomb corrections, and use this result to obtain approximate next-to-next-to-next-to-leading order predictions for the total top-quark pair-production cross section at the LHC. We generalize a required one-loop potential in non-relativistic QCD to the colour-octet case and estimate the remaining unknown two-loop potentials and three-loop anomalous dimensions. We obtain a moderate correction of $1.5\%$ relative to the next-to-next-to-leading order prediction and observe a reduction of the perturbative uncertainty below $\pm 5\%$.Comment: 47 pages, 5 figures, v2: published version, typos corrected (including scale uncertainties in Eqs. (4.16)-(4.20)), references added; v3: see added note on p.30 for changes; the results of this work are implemented in the program TOPIXS, which can be found at http://users.ph.tum.de/t31software/topixs

Mixed QCD-electroweak O(\alpha_s\alpha) corrections to Drell-Yan processes in the resonance region: pole approximation and non-factorizable corrections

Drell-Yan-like W-boson and Z-boson production in the resonance region allows for high-precision measurements that are crucial to carry experimental tests of the Standard Model to the extremes, such as the determination of the W-boson mass and the effective weak mixing angle. In this article, we establish a framework for the calculation of the mixed QCD-electroweak O(\alpha_s\alpha) corrections to Drell-Yan processes in the resonance region, which are one of the main remaining theoretical uncertainties. We describe how the Standard Model prediction can be successfully performed in terms of a consistent expansion about the resonance poles, which classifies the corrections in terms of factorizable and non-factorizable contributions. The former can be attributed to the W/Z production and decay subprocesses individually, while the latter link production and decay by soft-photon exchange. At next-to-leading order we compare the full electroweak corrections with the pole-expanded approximations, confirming the validity of the approximation. At O(\alpha_s\alpha), we describe the concept of the expansion and explicitly give results on the non-factorizable contributions, which turn out to be phenomenologically negligible. Our results, thus, demonstrate that for phenomenological purposes the O(\alpha_s\alpha) corrections can be factorized into terms associated with initial-state and/or final-state corrections. Moreover, we argue that the factorization properties of the non-factorizable corrections at O(\alpha_s\alpha) from lower-order O(\alpha_s) graphs generalize to any order in O(\alpha_s^n\alpha).Comment: 56 pages, 22 figure