759 research outputs found

    The Muon Decay at the Two Loop Level of the Electroweak Interactions

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    The progress in the evaluation of the muon decay lifetime is reviewed. The electroweak bosonic corrections are given together with the respective shift of the W boson mass. After inclusion of the recently corrected fermionic contributions, this requires an updated fitting formula for the prediction of MW.Comment: Invited talk at the XXIII Physics in Collisions Conference (PIC03), Zeuthen, Germany, June 2003, 3 pages, LaTeX, 2 eps figures. PSN FRAP2

    The soft function for color octet production at threshold

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    We evaluate the next-to-next-to-leading order soft function for the production of a massive color octet state at rest in the collision of two massless colored partons in either the fundamental or the adjoint representation. The main application of our result is the determination of the threshold expansion of the heavy-quark pair-production cross sections in the quark annihilation and gluon fusion channels. We discuss the factorization necessary for this purpose and explain the relationship between hard functions and virtual amplitudes.Comment: 18 pages, 5 figures, references added, matches published versio

    Single chargino production with R-parity lepton number violation in electron-electron and muon-muon collisions

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    We examine single chargino production in conjunction with R-parity lepton number violation in future lepton-lepton collisions. Present bounds on R-parity violating couplings allow for a production cross section of the order of O(10fb){\cal{O}} (10 {fb}) for a wide range of sneutrino and chargino masses. Scenarios of chargino decay which lead to purely leptonic signals in the final state and without missing energy are also discussed.Comment: Unfortunate mistake in the list of authors corrected, 10 pages, 4 figure

    Four-dimensional formulation of the sector-improved residue subtraction scheme

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    Four years ago, one of us introduced a novel subtraction scheme for the evaluation of double-real radiation contributions to cross sections at next-to-next-to-leading order (NNLO) in QCD. This approach, named SecToR Improved Phase sPacE for Real radiation (STRIPPER), has already found several non-trivial applications. In particular, it has allowed for the determination of NNLO corrections to hadronic top-quark pair production, fully differential top-quark decays, inclusive semileptonic charmless b-quark decays, associated Higgs boson and jet production in gluon fusion, muon decay spin asymmetry, and t-channel single-top production. Common to these calculations was the use of conventional dimensional regularization (CDR). In this publication, we present a complete formulation of the subtraction scheme for arbitrary processes with any number of colored partons in the final state, and up to two partons in the initial state. Furthermore, we modify the integrated subtraction terms of the double-real radiation to enable the introduction of the 't Hooft-Veltman version of dimensional regularization (HV), in which resolved states are four-dimensional. We demonstrate the correctness of our approach on the example of top-quark pair production in the gluon fusion channel.Comment: 60 pages, 5 figures, 9 table

    Differential equations and massive two-loop Bhabha scattering: the B5l2m3 case

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    The two-loop box contributions to massive Bhabha scattering may be reduced to two-loop box master integrals (MIs) with five, six, and seven internal lines, plus vertices and self energies. The self-energy and vertex MIs may be solved analytically by the differential equations (DE) method. This is true for only few of the box masters. Here we describe some details of the analytical determination, including constant terms in ep=(4-d)/2, of the complicated topology B5l2m3 (with 5 lines, 2 of them being massive). With the DE approach, three of the four coupled masters have been solved in terms of (generalized) standard Harmonic Polylogarithms.Comment: 5 pages, 2 figures, contribution to RADCOR 2005, Oct 2-7, 2005, Shonan Village, Japan, to appear in Nucl. B (Proc. Suppl.

    W Pair Production at the LHC - I. Virtual O(alpha_s^2) Corrections in the High Energy Limit

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    We present the result for the two-loop and the one-loop squared virtual QCD corrections to the W boson pair production in the quark-anti-quark-annihilation channel in the limit where all kinematical invariants are large compared to the mass of the W boson. The infrared pole structure is in agreement with the prediction of Catani's general formalism for the singularities of two loop amplitudes.Comment: 22 pages, 1 figure, references added, typos corrected, final version as publishe

    Threshold Resummation for Top-Pair Hadroproduction to Next-to-Next-to-Leading Log

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    We derive the threshold-resummed total cross section for heavy quark production in hadronic collisions accurate to next-to-next-to-leading logarithm, employing recent advances on soft anomalous dimension matrices for massive pair production in the relevant kinematic limit. We also derive the relation between heavy quark threshold resummations for fixed pair kinematics and the inclusive cross section. As a check of our results, we have verified that they reproduce all poles of the color-averaged q\bar{q} -> t\bar{t} amplitudes at two loops, noting that the latter are insensitive to the color-antisymmetric terms of the soft anomalous dimension.Comment: 18 pages; Expanded discussion, added references. Results unchanged
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