672 research outputs found
Tests of Higgs Boson Couplings at a mu+mu- Collider
We investigate the potential of a muon collider for testing the presence of
anomalous Higgs boson couplings. We consider the case of a light (less than
) Higgs boson and study the effects on the Higgs branching ratios and
total width, which could be induced by the non standard couplings created by a
class of dim=6 gauge invariant operators
satisfying the constraints imposed by the present and future hadronic and
colliders. For each operator we give the minimal value of the
integrated luminosity needed for the muon collider () to
improve these constraints. Depending on the operator and the Higgs mass, this
minimal luminosity lies between and .Comment: 18 pages and 4 figures; version to be published in Phys. Rev.D.
e-mail: [email protected]
Testing the Higgs boson gluonic couplings at LHC
We study Higgs + jet production at hadron colliders in order to look for new
physics residual effects possibly described by the operators
{\O}_{GG} and {\widetilde\O}_{GG} which induce anomalous and
couplings. Two ways for constraining these operators at LHC may be ~useful. The
first is based on the total Higgs boson production rate induced by gluon-gluon
fusion, in which the main cause of limitations are due to theoretical
uncertainties leading to sensitivities of and
for the corresponding anomalous
couplings, in the mass range 100 GeV \lsim \mh \lsim 2~00 GeV. These results
imply sensitivity to new physics scales of 51 and 24 TeV respectively. The
second way investigated here concerns the shape of the Higgs transverse
momentum; for which the theoretical uncertainties are less severe and the
limitations are mainly induced by statistics. A simple analysis, based on the
ratio of the number of events at large and low at LHC, leads to similar
sensitivities, if only the decay mode is used. But the
sensitivities can now be improved by a factor 2 to 10, depending on the Higgs
mass, if the Higgs decay modes to , , , are also used.Comment: 23 pages and 7 figures, version to appear in Phys.ReV.D. e-mail:
[email protected]
Signatures of the anomalous and ZZ production at the lepton and hadron Colliders
The possible form of New Physics (NP) interactions affecting the ZZZ, and vertices, is critically examined. Their signatures
and the possibilities to study them, through ZZ and production, at
the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC,
are investigated. Experimental limits obtained or expected on each coupling are
collected. A simple theoretical model based on virtual effects due to some
heavy fermions is used for acquiring some guidance on the plausible forms of
these NP vertices. In such a case specific relations among the various neutral
couplings are predicted, which can be experimentally tested and possibly used
to constrain the form of the responsible NP structure.Comment: 17 pages and 9 figures, version to appear in Phys. ReV. e-mail:
[email protected]
Vector boson Pair Production at Supercolliders; useful approximate helicity amplitudes
We study vector boson pair production at and , taking into account
the effects generated by the anomalous vector boson and Higgs couplings induced
by the operators and , which are the only dim=6
operators preserving . These operators lead to enhanced production of
transverse vector bosons, as opposed to the enhanced production of longitudinal
gauge bosons, induced in case M_H\gsim 1\ TeV, by dim=4 terms already
existing in the Standard Model lagrangian. For vector boson pair masses larger
than , we establish very simple approximate expressions for the
standard as well as the non-standard helicity amplitudes for
annihilation and vector boson fusion, which accurately describe the physics.
These expressions should simplify the experimental search for such
interactions. We finally discuss the observability and the disentangling of
these interactions.Comment: 22 pages, 6 figures avaible by air mail upon request , (e-mail
[email protected] PM/93-26 THES-TP 93/
Unitarity Constraints for New Physics Induced by dim-6 Operators
We compute the helicity amplitudes for boson-boson scattering at high energy
due to the operators \O_{B\Phi}, \O_{W\Phi} and \O_{UB}, and we derive
the corresponding unitarity bounds. Thus, we provide relations between the
couplings of these operators and the corresponding New Physics thresholds,
where either unitarity is saturated or new degrees of freedom are excited. We
compare the results with those previously obtained for the operators \O_W and
\O_{UW} and we discuss their implications for direct and indirect tests at
present and future colliders. The present treatment completes the study of the
unitarity constraints for all blind bosonic operators.Comment: 41 pages, latex file. PM 94-28 THES-TP 94-0
On the Interpretation of the Electroweak Precision Data
The recent precision electroweak data on and
are compared with the tree-level and the dominant-fermion-loop as well as the
full one-loop standard-model predictions. While the tree-level predictions are
ruled out, the dominant-fermion-loop predictions, defined by using in the tree-level formulae, as well as the full one-loop
predictions are consistent with the experimental data. Deviations from the
dominant-fermion-loop predictions are quantified in terms of an effective
Lagrangian containing three additional parameters which have a simple meaning
in terms of symmetry violation. The effective Lagrangian yields the
standard one-loop predictions for specific values of these parameters, which
are determined by and .Comment: Preprint BI-TP 93/46 (September 1993), to be published in Phys. Lett.
B, LaTeX, 10 pages, (figures are not included
A FORTRAN code for in SM and MSSM
Through the present paper, the code gamgamZZ is presented, which may be used
to calculate all possible observables related to the process , in either the Standard Model (SM), or the minimal sypersymmetric standard
model (MSSM) with real parameters.Comment: 13 pages, 7 figures Revised according to the EPJC Referee suggestion
Probing the Weak Boson Sector in
We study possible deviations from the standard model in the reaction at a 500 GeV collider. As a photon source we use a
laser backscattered photon beam. We investigate the most general and vertices including operators up to
energy-dimension-six which are Lorentz invariant. These vertices require four
extra parameters; two are CP-conserving, and , and two are
CP-violating, and . We present analytical expressions of
the helicity amplitudes for the process for arbitrary
values of anomalous couplings. Assuming Standard Model values are actually
measured we present the allowed region in the () plane at the
90\% confidence level. We then show how the angular correlation of the
decay products can be used to extract detailed information on the anomalous
(especially CP-violating) and couplings.Comment: Latex, 25 pages, 12 figures (not included). One compressed postscript
file including all the figures available at
ftp://ftp.kek.jp/kek/preprints/TH/TH-420/kekth420.ps.g
QCD Corrections to Electroweak Vector Boson Scattering at Small Scattering Angles
We investigate the role of a certain class of QCD corrections to electroweak
vector boson scattering at small scattering angles and large energies. These
are present since, from the perturbative analysis, the vector bosons may
dissociate into quark-antiquark pairs giving rise to colour dipoles interacting
through gluon exchanges. After the computation of the vector boson impact
factors, we present expressions for the lowest order QCD scattering amplitude
and for the leading logarithmic BFKL amplitude. Particularly we discuss
numerical results for the process . The QCD corrections to
the cross section resulting from the interference with the electroweak ones are
estimated and compared with the leading pure electroweak part. Corrections
resulting from the leading log BFKL amplitude are of the order of few percent
already at the TeV energy range.Comment: 21 pages,9 figures, discussion on the helicity-flip impact factors
added, typos correcte
New Physics Signatures in Dijets at Hadron Colliders
We show how to detect and disentangle at the upgraded Tevatron and at LHC,
the effects of the three purely gluonic
CP-conserving and CP-violating gauge invariant operators \ol{\O}_{DG}, \O_G
and \wtil{\O}_{G}. These operators are inevitably generated by New Physics
(NP), if the heavy particles responsible for it are coloured. We establish the
relations between their coupling constants and the corresponding NP scales
defined through the unitarity relations. We then study the sensitivity and
limits obtainable through production processes involving one or two jets, and
express these limits in terms of the NP scales implied by unitarity. A detailed
comparison with the results of the studies of the analogous electroweak
operators, is also made.Comment: 19 pages and 3 figures, version to appear in Phys.ReV.D. e-mail:
[email protected]
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