1,467 research outputs found
Electroweak and QCD corrections to Higgs production via vector-boson fusion at the LHC
The radiative corrections of the strong and electroweak interactions are
calculated at next-to-leading order for Higgs-boson production in the
weak-boson-fusion channel at hadron colliders. Specifically, the calculation
includes all weak-boson fusion and quark--antiquark annihilation diagrams to
Higgs-boson production in association with two hard jets, including all
corresponding interferences. The results on the QCD corrections confirm that
previously made approximations of neglecting s-channel diagrams and
interferences are well suited for predictions of Higgs production with
dedicated vector-boson fusion cuts at the LHC. The electroweak corrections,
which also include real corrections from incoming photons and leading
heavy-Higgs-boson effects at two-loop order, are of the same size as the QCD
corrections, viz. typically at the level of 5-10% for a Higgs-boson mass up to
\sim 700 GeV. In general, both types of corrections do not simply rescale
differential distributions, but induce distortions at the level of 10%. The
discussed corrections have been implemented in a flexible Monte Carlo event
generator.Comment: 33 pages, LaTeX, 24 postscript figure
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
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
Gauge-independent renormalization in the 2HDM
We present a consistent renormalization scheme for the CP-conserving
Two-Higgs-Doublet Model based on renormalization of the mixing
angles and the soft--symmetry-breaking scale in the Higgs sector.
This scheme requires to treat tadpoles fully consistently in all steps of the
calculation in order to provide gauge-independent -matrix elements. We show
how bare physical parameters have to be defined and verify the gauge
independence of physical quantities by explicit calculations in a general
-gauge. The procedure is straightforward and applicable to other
models with extended Higgs sectors. In contrast to the proposed scheme, the
renormalization of the mixing angles combined with popular
on-shell renormalization schemes gives rise to gauge-dependent results already
at the one-loop level. We present explicit results for electroweak NLO
corrections to selected processes in the appropriately renormalized
Two-Higgs-Doublet Model and in particular discuss their scale dependence.Comment: 52 pages, PDFLaTeX, PDF figures, JHEP version with Eq. (5.23)
correcte
Precision Predictions for (Un)Stable W+W- Pair Production At and Beyond LEP2 Energies Beyond LEP2 Energies
We present precision calculations of the processes e+e- -> 4-fermions in
which the double resonant W+W- intermediate state occurs. Referring to this
latter intermediate state as the 'signal process', we show that, by using the
YFS Monte Carlo event generators YFSWW3-1.14 and KORALW1.42 in an appropriate
combination, we achieve a physical precision on the signal process, as isolated
with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge
invariance of our calculations and we compare our results with those of other
authors where appropriate. In particular, sample Monte Carlo data are
explicitly illustrated and compared with the results of the program RacoonWW of
Dittmaier {\it et al.}. In this way, we show that the total (physical plus
technical) precision tag for the WW signal process cross section is 0.4 per
cent for 200 GeV, for example. Results are also given for 500 GeV with an eye
toward the LC.Comment: 19 pages, 2 figs;corrected Tab. 3;improved refs.,figs.,text;improved
refs.,text;improved tex
Photon Radiation with MadDipole
We present the automation of a subtraction method for photon radiation using
the dipole formalism within the MadGraph framework. The subtraction terms are
implemented both in dimensional regularization and mass regularization for
massless and massive cases and non-collinear-safe observables are accounted
for.Comment: 23 pages, 2 figures, minor additions, references added, version
published in JHE
Radiative Corrections to ZZ->ZZ in the Electroweak Standard Model
The cross-section for ZZ->ZZ with arbitrarily polarized Z bosons is
calculated within the electroweak Standard Model including the complete
O(alpha) corrections. We show the numerical importance of the radiative
corrections and elaborate its characteristic features. The treatment of the
Higgs-boson resonance is discussed in different schemes including the
S-matrix-motivated pole scheme and the background-field method. The numerical
accuracy of the equivalence theorem is investigated by comparing the
cross-sections for purely longitudinal Z bosons obtained from the equivalence
theorem and from the complete calculation. In this context the full O(alpha)
corrections are also confronted with the enhanced corrections of O(alpha
M_H^2/s_w^2 M_W^2), which were frequently used in the literature.Comment: 35 pages LaTeX, 19 postscript figures include
Charged Higgs Production in the 1 TeV Domain as a Probe of Supersymmetric Models
We consider the production, at future lepton colliders, of charged Higgs
pairs in supersymmetric models. Assuming a relatively light SUSY scenario, and
working in the MSSM, we show that, for c.m. energies in the one TeV range, a
one-loop logarithmic Sudakov expansion that includes an "effective" next-to
subleading order term is adequate to the expected level of experimental
accuracy. We consider then the coefficient of the linear (subleading) SUSY
Sudakov logarithm and the SUSY next to subleading term of the expansion and
show that their dependence on the supersymmetric parameters of the model is
drastically different. In particular the coefficient of the SUSY logarithm is
only dependent on while the next to subleading term depends on a
larger set of SUSY parameters. This would allow to extract from the data
separate informations and tests of the model.Comment: 18 pages and 13 figures e-mail: [email protected]
Feynman rules for the rational part of the Electroweak 1-loop amplitudes
We present the complete set of Feynman rules producing the rational terms of
kind R_2 needed to perform any 1-loop calculation in the Electroweak Standard
Model. Our results are given both in the 't Hooft-Veltman and in the Four
Dimensional Helicity regularization schemes. We also verified, by using both
the 't Hooft-Feynman gauge and the Background Field Method, a huge set of Ward
identities -up to 4-points- for the complete rational part of the Electroweak
amplitudes. This provides a stringent check of our results and, as a
by-product, an explicit test of the gauge invariance of the Four Dimensional
Helicity regularization scheme in the complete Standard Model at 1-loop. The
formulae presented in this paper provide the last missing piece for completely
automatizing, in the framework of the OPP method, the 1-loop calculations in
the SU(3) X SU(2) X U(1) Standard Model.Comment: Many thanks to Huasheng Shao for having recomputed, independently of
us, all of the effective vertices. Thanks to his help and by
comparing with an independent computation we performed in a general
gauge, we could fix, in the present version, the following formulae: the
vertex in Eq. (3.6), the vertex in Eq. (3.8),
Eqs (3.16), (3.17) and (3.18
Finite-width effects in the near-threshold ZZZ and ZWW production at ILC
We calculate the cross-section of the near-threshold off-shell and
production at the International Linear Collider taking into account
their instability and the principal part of NLO corrections. The calculations
are performed in the framework of the model of unstable particles with smeared
mass-shell. We show that the contribution of the finite and widths
(their instability) is large in the Higgs resonance range and should be taken
into account in the Higgs boson searches at future colliders.Comment: 5 pages, 6 figure
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