370 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]
Coherent pion production by neutrinos on nuclei
The main part of coherent pion production by neutrinos on nuclei is
essentially determined by PCAC, provided that the leptonic momentum transferred
square Q^2 remains sufficiently small. We give the formulas for the charged and
neutral current cross sections, including also the small non-PCAC transverse
current contributions and taking into account the effect of the \mu^- mass. Our
results are compared with the experimental ones and other theoretical
treatments.Comment: 18 pages, 4 figure
The Equivalence Theorem and Effective Lagrangians
We point out that the equivalence theorem, which relates the amplitude for a
process with external longitudinally polarized vector bosons to the amplitude
in which the longitudinal vector bosons are replaced by the corresponding
pseudo-Goldstone bosons, is not valid for effective Lagrangians. However, a
more general formulation of this theorem also holds for effective interactions.
The generalized theorem can be utilized to determine the high-energy behaviour
of scattering processes just by power counting and to simplify the calculation
of the corresponding amplitudes. We apply this method to the phenomenologically
most interesting terms describing effective interactions of the electroweak
vector and Higgs bosons in order to examine their effects on vector-boson
scattering and on vector-boson-pair production in annihilation. The
use of the equivalence theorem in the literature is examined.Comment: 20 pages LaTeX, BI-TP 94/1
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
Full order alpha electroweak corrections to double Higgs-strahlung at the linear collider
We present the full order alpha electroweak radiative corrections to the
double Higgs-strahlung process e+e- --> ZHH. The computation is performed with
the help of GRACE-loop. After subtraction of the initial state QED radiative
corrections, we find that the genuine weak corrections in the -scheme
are small for Higgs masses and energies where this cross section is largest and
is most likely to be studied. These corrections decrease with increasing
energies attaining about at TeV. The full order alpha
correction on the other hand is quite large at threshold but small at energies
around the peak. We also study changes in the shape of the invariant mass of
the Higgs pair which has been shown to be a good discriminating variable for
the measurement of the triple Higgs vertex in this reaction.Comment: 18 pages, 5 figures and 3 table
The neutralino projector formalism for complex SUSY parameters
We present a new formalism describing the neutralino physics in the context
of the minimal supersymmetric model (MSSM), where CP violation induced by
complex and parameters is allowed. The formalism is based on the
construction of neutralino projectors, and can be directly generalized to
non-minimal SUSY models involving any number of neutralinos. It extends a
previous work applied to the real SUSY parameter case. In MSSM, the method
allows to describe all physical observables related to a specific neutralino,
in terms of its
CP eigenphase and three complex numbers called its "reduced projector
elements".
As the experimental knowledge on the neutralino-chargino sectors will be
being accumulated, the problem of extracting the various SUSY parameters will
arise. Motivated by this, we consider various scenarios concerning the
quantities that could be first measured. Analytical disentangled expressions
determining the related SUSY parameters from them, are then derived, which also
emphasize the efficiency of the formalism.Comment: Version accepted in Phys. Rev. D. e-mail: [email protected]
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]
Progress on a spherical TPC for low energy neutrino detection
The new concept of the spherical TPC aims at relatively large target masses
with low threshold and background, keeping an extremely simple and robust
operation. Such a device would open the way to detect the neutrino-nucleus
interaction, which, although a standard process, remains undetected due to the
low energy of the neutrino-induced nuclear recoils. The progress in the
development of the fist 1 m prototype at Saclay is presented. Other physics
goals of such a device could include supernova detection, low energy neutrino
oscillations and study of non-standard properties of the neutrino, among
others.Comment: 3 pages, talk given at the 9th Workshop on Topics in Astroparticle
and Underground Physics, Zaragoza, September 10-1
Neutrinos in a spherical box
In the present paper we study some neutrino properties as they may appear in
the low energy neutrinos emitted in triton decay with maximum neutrino energy
of 18.6 keV. The technical challenges to this end can be achieved by building a
very large TPC capable of detecting low energy recoils, down to a a few tenths
of a keV, within the required low background constraints. More specifically We
propose the development of a spherical gaseous TPC of about 10-m in radius and
a 200 Mcurie triton source in the center of curvature. One can list a number of
exciting studies, concerning fundamental physics issues, that could be made
using a large volume TPC and low energy antineutrinos: 1) The oscillation
length involving the small angle of the neutrino mixing matrix, directly
measured in this disappearance experiment, is fully contained inside the
detector. Measuring the counting rate of neutrino-electron elastic scattering
as a function of the distance of the source will give a precise and unambiguous
measurement of the oscillation parameters free of systematic errors. In fact
first estimates show that even with a year's data taking a sensitivity of a few
percent for the measurement of the above angle will be achieved. 2) The low
energy detection threshold offers a unique sensitivity for the neutrino
magnetic moment which is about two orders of magnitude beyond the current
experimental limit. 3) Scattering at such low neutrino energies has never been
studied and any departure from the expected behavior may be an indication of
new physics beyond the standard model. In this work we mainly focus on the
various theoretical issues involved including a precise determination of the
Weinberg angle at very low momentum transfer.Comment: 16 Pages, LaTex, 7 figures, talk given at NANP 2003, Dubna, Russia,
June 23, 200
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