835 research outputs found
The Muon Decay at the Two Loop Level of the Electroweak Interactions
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
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
Four-dimensional formulation of the sector-improved residue subtraction scheme
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
Single chargino production with R-parity lepton number violation in electron-electron and muon-muon collisions
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
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
Differential equations and massive two-loop Bhabha scattering: the B5l2m3 case
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.
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