1,850 research outputs found
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
Higgs Production via Gluon-Induced Weak Boson Fusion
We present a calculation that allows for an estimation of the NNLO
contributions to the Higgs production in the weak boson fusion channel. A
possible deterioration of this important channel for the Higgs discoveries at
the LHC can be ruled out by this calculation due to the small remaining cross
section after the weak boson cuts.Comment: 4 pages, 3 figures. To appear in the proceedings of the 14th
International QCD Conference (QCD 08), Montpellier, France, 7-12 July 200
Electroweak corrections and anomalous triple gauge-boson couplings in WW and WZ production at the LHC
We have analysed the production of WW and WZ vector-boson pairs at the LHC.
These processes give rise to four-fermion final states, and are particularly
sensitive to possible non-standard trilinear gauge-boson couplings. We have
studied the interplay between the influence of these anomalous couplings and
the effect of the complete logarithmic electroweak O(\alpha) corrections.
Radiative corrections to the Standard Model processes in double-pole
approximation and non-standard terms due to trilinear couplings are implemented
into a Monte Carlo program for p p -> 4f (+\gamma) with final states involving
four or two charged leptons. We numerically investigate purely leptonic final
states and find that electroweak corrections can fake new-physics signals,
modifying the observables by the same amount and shape, in kinematical regions
of statistical significance.Comment: 19 pages, LaTex, 12 eps figure
About helicity conservation in gauge boson scattering at high energy
We remark that the high energy gauge boson scattering processes involving
two-body initial and final states, satisfy certain selection rules described as
helicity conservation of the \underline{gauge boson} amplitudes (GBHC). These
rules are valid at Born level, as well as at the level of the leading and
sub-leading 1-loop logarithmic corrections, in both the Standard Model (SM) and
the Minimal Supersymmetric Standard Model (MSSM). A "fermionic equivalence"
theorem is also proved, which suggests that GBHC is valid at all orders in MSSM
at sufficiently high energies, where the mass suppressed contributions are
neglected.Comment: 7 pages, 2 figures, version to appear in Phys. Rev. Letter
On the tensor reduction of one-loop pentagons and hexagons
We perform analytical reductions of one-loop tensor integrals with 5 and 6
legs to scalar master integrals. They are based on the use of recurrence
relations connecting integrals in different space-time dimensions. The
reductions are expressed in a compact form in terms of signed minors, and have
been implemented in a mathematica package called hexagon.m. We present several
numerical examples.Comment: Latex, 7 pages, 2 eps figures. Contribution to the proceedings of
`Loops and Legs in Quantum Field Theory', April 2008, Sondershausen, German
Four-fermion production with RACOONWW
RACOONWW is an event generator for e+e- --> WW --> 4fermions(+gamma) that
includes full tree-level predictions for e+e- --> 4f and e+e- --> 4f+gamma as
well as O(alpha) corrections to e+e- --> 4f in the so-called double-pole
approximation. We briefly sketch the concept of the calculation on which this
generator is based and present some numerical results.Comment: 9 pages, latex, 6 postscript files, to appear in the proceedings of
the UK Phenomenology Workshop on Collider Physics, Durham, UK, 19-24
September, 199
Flavor-Changing Top Quark Rare Decays in the Littlest Higgs Model with T-Parity
We analyze the rare and flavor changing decay of the top quark into a charm
quark and a gauge boson in the littlest Higgs model with T-parity (LHT). We
calculate the one-loop level contributions from the T-parity odd mirror quarks
and gauge bosons. We find that the decay in the LHT
model can be significantly enhanced relative to those in the Standard Model.
Our numerical results show that the top quark FCNC decay can be as large as
, and in the favorite parameter space in the LHT model.Comment: 12 pages, 3 figure
Unstable particle's wave-function renormalization prescription
We strictly define two set Wave-function Renormalization Constants (WRC)
under the LSZ reduction formula for unstable particles at the first time. Then
by introducing antiparticle's WRC and the CPT conservation law we obtain a new
wave-function renormalization condition which can be used to totally determine
the two set WRC. We calculate two physical processes to manifest the
consistence of the present wave-function renormalization prescription with the
gauge theory in standard model. We also prove that the conventional
wave-function renormalization prescription which discards the imaginary part of
unstable particle's WRC leads to physical amplitude gauge dependent.Comment: 10 pages, 3 figure
Electroweak-correction effects in gauge-boson pair production at the LHC
We have studied the effect of one-loop logarithmic electroweak radiative
corrections on WZ and production processes at the LHC. We present
analytical results for the leading-logarithmic electroweak corrections to the
corresponding partonic processes du -> WZ, Wgamma. Using the leading-pole
approximation we implement these corrections into Monte Carlo programs for
. We find that electroweak corrections
lower the predictions by 5-20% in the physically interesting region of large
transverse momentum and small rapidity separation of the gauge bosons.Comment: 28 pages, LaTex, 13 eps figures included; references added and
corrected typo
Electroweak corrections to Higgs-strahlung off W/Z bosons at the Tevatron and the LHC with HAWK
The associate production of Higgs bosons with W or Z bosons, known as
Higgs-strahlung, is an important search channel for Higgs bosons at the hadron
colliders Tevatron and LHC for low Higgs-boson masses. We refine a previous
calculation of next-to-leading-order electroweak corrections (and recalculate
the QCD corrections) upon including the leptonic decay of the W/Z bosons,
thereby keeping the fully differential information of the 2-lepton + Higgs
final state. The gauge invariance of the W/Z-resonance treatment is ensured by
the use of the complex-mass scheme. The electroweak corrections, which are at
the level of -(5-10)% for total cross sections, further increase in size with
increasing transverse momenta p_T in differential cross sections. For instance,
for p_T,H >~ 200GeV, which is the interesting range at the LHC, the electroweak
corrections to WH production reach about -14% for M_H = 120GeV. The described
corrections are implemented in the HAWK Monte Carlo program, which was
initially designed for the vector-boson-fusion channel, and are discussed for
various distributions in the production channels pp / p \bar p -> H + l nu_l /
l^-l^+ / nu_l \bar nu_l + X.Comment: 22 p
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