2,049 research outputs found
Electroweak Corrections to e+e- --> 4 fermions
The calculation of the full electroweak O(alpha) corrections to the
charged-current four-fermion production processes e+e- --> nu_tau tau+ mu-
anti-nu_mu, u anti-d mu- anti-nu_mu, and u anti-d s anti-c is briefly reviewed.
The calculation is performed using the complex-mass scheme for the gauge-boson
resonances. The evaluation of the occurring one-loop tensor integrals, which
include 5- and 6-point functions, requires new techniques. The effects of the
complete O(alpha) corrections to the total cross section and to the
production-angle distribution are discussed and compared to predictions based
on the double-pole approximation, revealing that the latter approximation is
not sufficient to fully exploit the potential of a future linear collider in an
analysis of W-boson pairs at high energies.Comment: 5 pages, LaTeX, 6 postscript figures, to appear in the proceedings of
the "7th International Symposium on Radiative Corrections (RADCOR05)", Shonan
Village, 200
Four-fermion production at gamma gamma colliders: 2. Radiative corrections in double-pole approximation
The O(alpha) electroweak radiative corrections to gamma gamma --> WW --> 4f
within the electroweak Standard Model are calculated in double-pole
approximation (DPA). Virtual corrections are treated in DPA, leading to a
classification into factorizable and non-factorizable contributions, and
real-photonic corrections are based on complete lowest-order matrix elements
for gamma gamma --> 4f + gamma. Soft and collinear singularities appearing in
the virtual and real corrections are combined alternatively in two different
ways, namely by using the dipole subtraction method or by applying phase-space
slicing. The radiative corrections are implemented in a Monte Carlo generator
called COFFERgammagamma, which optionally includes anomalous triple and quartic
gauge-boson couplings in addition and performs a convolution over realistic
spectra of the photon beams. A detailed survey of numerical results comprises
O(alpha) corrections to integrated cross sections as well as to angular,
energy, and invariant-mass distributions. Particular attention is paid to the
issue of collinear-safety in the observables.Comment: 42 pages, latex, 34 postscript figure
Radiative corrections to e+e- --> WW --> 4f with RACOONWW
RACOONWW is the first Monte Carlo generator for e+e- --> WW --> 4f(+gamma)
that includes the electroweak O(alpha) radiative corrections in the double-pole
approximation completely. Some numerical results for LEP2 energies are
discussed, and the predictions for the total W-pair cross section are
confronted with LEP2 data.Comment: 7 pages, latex, 5 postscript files, to appear in the Proceedings of
the 5th Zeuthen Workshop on Elementary Particle Theory ``Loops and Legs in
Quantum Field Theory'', Bastei/Koenigstein, Germany, April 9-14, 200
A Feynman diagram analyzer DIANA: recent development
New developments concerning the extension of the Feynman diagram analyzer
DIANA are presented. We discuss new graphic facilities, application of DIANA to
processes with Majorana fermions and different approaches to automation of
momenta distribution.Comment: 2 pages, Latex using espcrc2.sty, 3 figures using 3 eps files.
Contribution to ACAT 2002, Moscow, Russia, June 24-28, 200
Electroweak corrections to e+ e- -> f anti-f H
Some of the most interesting Higgs-production processes at future e+ e-
colliders are of the type e+ e- -> f anti-f H. We present a calculation of the
complete O(alpha) corrections to these processes in the Standard Model for
final-state neutrinos and top quarks. Initial-state radiation beyond O(alpha)
at the leading-logarithmic level as well as QCD corrections are also included.
The electroweak corrections turn out to be sizable and reach the order of
+/-10% and will thus be an important part of precise theoretical predictions
for future e+ e- colliders.Comment: 4 pages, LaTeX, 4 postscript figures, talk given at Loops and Legs
2004, 7th DESY Workshop on Elementary Particle Theory, Zinnowitz, German
Two-loop electroweak corrections at high energies
We discuss two-loop leading and angular-dependent next-to-leading logarithmic
electroweak virtual corrections to arbitrary processes at energies above the
electroweak scale. The relevant Feynman diagrams involving soft-collinear gauge
bosons gamma, Z, W, have been evaluated in eikonal approximation. We present
results obtained from the analytic evaluation of massive loop integrals. To
isolate mass singularities we used the Sudakov method and alternatively the
sector decomposition method in the Feynman-parameter representation.Comment: 5 pages. Talk presented by S.P. at the International Symposium on
Radiative Corrections RADCOR 2002, September 8-13, Kloster Banz, Germany. To
appear in the proceeding
RacoonWW1.3: A Monte Carlo program for four-fermion production at e^+ e^- colliders
We present the Monte Carlo generator RacoonWW that computes cross sections to
all processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma and calculates the
complete O(alpha) electroweak radiative corrections to e^+ e^- -> W W -> 4f in
the electroweak Standard Model in double-pole approximation. The calculation of
the tree-level processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma is based on
the full matrix elements for massless (polarized) fermions. When calculating
radiative corrections to e^+ e^- -> W W -> 4f the complete virtual
doubly-resonant electroweak corrections are included, i.e. the factorizable and
non-factorizable virtual corrections in double-pole approximation, and the real
corrections are based on the full matrix elements for e^+ e^- -> 4f + gamma.
The matching of soft and collinear singularities between virtual and real
corrections is done alternatively in two different ways, namely by using a
subtraction method or by applying phase-space slicing. Higher-order
initial-state photon radiation and naive QCD corrections are taken into
account. RacoonWW also provides anomalous triple gauge-boson couplings for all
processes e^+ e^- -> 4f and anomalous quartic gauge-boson couplings for all
processes e^+ e^- -> 4f + gamma.Comment: 62 pages, LaTeX, elsart styl
Impact of QED corrections to Higgs decay into four leptons at the LHC
At the LHC a precise measurement of the Higgs boson mass (if discovered), at
the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for
a wide range of Higgs mass values. To match such an accuracy, the systematic
effects induced by QED corrections need to be investigated. In the present
study the calculation of O(alpha) and higher order QED corrections is
illustrated as well as their impact on the Higgs mass determination, once
realistic event selection criteria for charged leptons and photons are
considered.Comment: 5 pages, 5 figures, 1 table. Presented at HEP2005 July 21st-27th,
2005, Lisboa, Portugal and at RADCOR 2005, Shonan Village, October 2nd-7th,
2005, Japa
Electroweak radiative corrections to e+ e- -> t anti-t H
We have calculated the complete electroweak O(alpha) radiative corrections to
the Higgs-boson production process e+ e- -> t anti-t H in the electroweak
Standard Model. Initial-state radiation beyond O(alpha) is included in the
structure-function approach. The calculation of the corrections is briefly
described, and numerical results are presented for the total cross section.
Both the photonic and the genuine weak corrections reach the order of about 10%
or even more and show a non-trivial dependence on the Higgs-boson mass and on
the scattering energy. We compare our results with two previous calculations
that obtained differing results at high energies.Comment: 13 pages, LaTeX, 12 postscript figure
Electroweak corrections to e+ e- -> nu anti-nu H and e+ e- -> t anti-t H
The most interesting Higgs-production processes at future e+ e- colliders
belong to the process class e+ e- -> f anti-f H. We study the full O(alpha)
corrections to this reaction in the Standard Model for neutrinos and top quarks
in the final state. Leading higher-order corrections from initial-state
radiation and QCD corrections are also taken into account. Although
cancellations between the different kinds of corrections occur, the full
corrections are of the order of +/-10% and thus important ingredients in the
theoretical predictions for future e+ e- colliders.Comment: 3 pages, LaTeX, 4 postscript figures, talk given at the EPS
conference, Aachen, 200
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