Electroweak non-resonant corrections to top pair production close to threshold

The production of W+ W- b bbar from e+ e- collisions at energies close to the t tbar threshold is dominated by the resonant process with a nearly on-shell t tbar intermediate state. The W b pairs in the final state can also be reached through the decay of off-shell tops or through background processes containing no or only single top quarks. This non-resonant production starts to contribute at NLO to the W+ W- b bbar total cross section in the non-relativistic power-counting v ~ alpha_s ~ sqrt(alpha_EW). The NLO non-resonant corrections presented in this talk represent the non-trivial NLO electroweak corrections to the e+ e- -> W+ W- b bbar cross section in the top anti-top resonance region. In contrast to the QCD corrections which have been calculated (almost) up to NNNLO, the parametrically larger NLO electroweak contributions have not been completely known so far, but are mandatory for the required accuracy at a future linear collider. We consider the total cross section of the e+ e- -> W+ W- b bbar process and additionally implement cuts on the invariant masses of the W+ b and W- bbar pairs.Comment: Talk presented at the 35th International Conference of High Energy Physics - ICHEP2010, July 22-28, 2010, Paris France. 4 pages, 2 figure

Soft-Collinear Factorization and Zero-Bin Subtractions

We study the Sudakov form factor for a spontaneously broken gauge theory using a (new) Delta -regulator. To be well-defined, the effective theory requires zero-bin subtractions for the collinear sectors. The zero-bin subtractions depend on the gauge boson mass M and are not scaleless. They have both finite and 1/epsilon contributions, and are needed to give the correct anomalous dimension and low-scale matching contributions. We also demonstrate the necessity of zero-bin subtractions for soft-collinear factorization. We find that after zero-bin subtractions the form factor is the sum of the collinear contributions 'minus' a soft mass-mode contribution, in agreement with a previous result of Idilbi and Mehen in QCD. This appears to conflict with the method-of-regions approach, where one gets the sum of contributions from different regions.Comment: 9 pages, 5 figures. V2:ref adde

Weak Boson Emission in Hadron Collider Processes

The O(alpha) virtual weak radiative corrections to many hadron collider processes are known to become large and negative at high energies, due to the appearance of Sudakov-like logarithms. At the same order in perturbation theory, weak boson emission diagrams contribute. Since the W and Z bosons are massive, the O(alpha) virtual weak radiative corrections and the contributions from weak boson emission are separately finite. Thus, unlike in QED or QCD calculations, there is no technical reason for including gauge boson emission diagrams in calculations of electroweak radiative corrections. In most calculations of the O(alpha) electroweak radiative corrections, weak boson emission diagrams are therefore not taken into account. Another reason for not including these diagrams is that they lead to final states which differ from that of the original process. However, in experiment, one usually considers partially inclusive final states. Weak boson emission diagrams thus should be included in calculations of electroweak radiative corrections. In this paper, I examine the role of weak boson emission in those processes at the Fermilab Tevatron and the CERN LHC for which the one-loop electroweak radiative corrections are known to become large at high energies (inclusive jet, isolated photon, Z+1 jet, Drell-Yan, di-boson, t-bar t, and single top production). In general, I find that the cross section for weak boson emission is substantial at high energies and that weak boson emission and the O(alpha) virtual weak radiative corrections partially cancel.Comment: revtex3, 41 pages, 16 figures, 3 table

Two-loop electroweak next-to-leading logarithmic corrections to massless fermionic processes

We consider two-loop leading and next-to-leading logarithmic virtual corrections to arbitrary processes with external massless fermions in the electroweak Standard Model at energies well above the electroweak scale. Using the sector-decomposition method and alternatively the strategy of regions we calculate the mass singularities that arise as logarithms of Q^2/MW^2, where Q is the energy scale of the considered process, and 1/\epsilon poles in D=4-2\epsilon dimensions, to one- and two-loop next-to-leading logarithmic accuracy. The derivations are performed within the complete electroweak theory with spontaneous symmetry breaking. Our results indicate a close analogy between the form of two-loop electroweak logarithmic corrections and the singular structure of scattering amplitudes in massless QCD. We find agreement with the resummation prescriptions that have been proposed in the literature based on a symmetric SU(2) \times U(1) theory matched with QED at the electroweak scale and provide new next-to-leading contributions proportional to ln(MZ^2/MW^2).Comment: 63 pages, LaTeX, references updated, some typos corrected, version to appear in Nucl. Phys.

The quantum Casimir operators of \Uq and their eigenvalues

We show that the quantum Casimir operators of the quantum linear group constructed in early work of Bracken, Gould and Zhang together with one extra central element generate the entire center of \Uq. As a by product of the proof, we obtain intriguing new formulae for eigenvalues of these quantum Casimir operators, which are expressed in terms of the characters of a class of finite dimensional irreducible representations of the classical general linear algebra.Comment: 10 page

Radiative Corrections to Longitudinal and Transverse Gauge Boson and Higgs Production

Radiative corrections to gauge boson and Higgs production computed recently using soft-collinear effective theory (SCET) require the one-loop high-scale matching coefficients in the standard model. We give explicit expressions for the matching coefficients for the effective field theory (EFT) operators for q qbar -> VV and q qbar -> phi^+ phi for a general gauge theory with an arbitrary number of gauge groups. The group theory factors are given explicitly for the standard model, including both QCD and electroweak corrections.Comment: 16 pages, 49 figure

Electroweak Sudakov Corrections using Effective Field Theory

Electroweak Sudakov corrections of the form alpha^n log^m s/M_{W,Z}^2 are summed using renormalization group evolution in soft-collinear effective theory (SCET). Results are given for the scalar, vector and tensor form-factors for fermion and scalar particles. The formalism for including massive gauge bosons in SCET is developed.Comment: 5 page