233 research outputs found
Static quantities of a neutral bilepton in the 331 model with right-handed neutrinos
A neutral vector boson can possess static electromagnetic properties provided
that the associated field is no self-conjugate. This possibility is explored in
the model with right-handed neutrinos, which
predicts a complex neutral gauge boson in a nontrivial representation of
the electroweak group. In this model the only nonvanishing form factors are the
CP-even ones, which arise from both the quark and gauge sectors, and contribute
to the magnetic dipole and the electric quadrupole moments of this neutral
particle.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Searching for Invisible and Almost Invisible Particles at e^+e^- Colliders
We explore the techniques, cross sections and expected signal significance
for detecting invisible and almost invisible particles at LEP2 and the NLC by
means of a hard photon tag. Examples from supersymmetry include the lightest
chargino and second lightest neutralino when their masses are nearly the same
as that of the lightest neutralino (the LSP), and invisibly decaying
sneutrinos. The importance of particular features of the detectors is
discussed, instrumentation for vetoing a fast e^+ or e^- in the beam hole being
especially crucial.Comment: 11 pages, 2 figures, latex, corrections (as outlined in recent
Addendum [hep-ph/9902309]) to the treatment of the decay of the lightest
chargino to the lightest neutralino, when they are closely degenerate in
mass, are implemented, and the associated minor changes in phenomenology are
incorporate
Fermion contribution to the static quantities of arbitrarily charged vector bosons
We present an analysis of the one-loop contribution from left- and
right-handed fermions to the static electromagnetic properties of an
arbitrarily charged no self-conjugate vector boson . Particular emphasis is
given to the case of a no self-conjugate neutral boson . Regardless the
electric charge of the boson, a fermionic loop can induce the two CP-even
form factors but only one CP-odd. As a result the corresponding electric dipole
moment is directly proportional to the magnetic quadrupole moment. The CP-odd
form factor might be severely suppressed since it requires the presence of both
left- and right-handed fermions. The behavior of the form factors is analyzed
for several scenarios of the fermion masses in the context of the decoupling
theorem.Comment: 12 pages, 3 figures, submitted to Journal of Physics
Large Tree Level CP Violation in in The Two Higgs Doublet Model
We find a large CP violation effect within the Two-Higgs-Doublet-Model for
the reaction at future linear colliders. The
CP-asymmetry arises already at the tree level as a result of interference
between diagrams with emission from (and ) and its emission
from a and can be about 10--20\%. In the best case one needs a few
hundred events to observe CP violation at the 3 level.Comment: UU encoded tar compressed tex file with postscript figure
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]
How Big Can Anomalous W Couplings Be?
Conventional wisdom has it that anomalous gauge-boson self-couplings can be
at most a percent or so in size. We test this wisdom by computing these
couplings at one loop in a generic renormalizable model of new physics. (For
technical reasons we consider the CP-violating couplings here, but our results
apply more generally.) By surveying the parameter space we find that the
largest couplings (several percent) are obtained when the new particles are at
the weak scale. For heavy new physics we compare our findings with expectations
based on an effective-lagrangian analysis. We find general patterns of induced
couplings which robustly reflect the nature of the underlying physics. We build
representative models for which the new physics could be first detected in the
anomalous gauge couplings.Comment: 40 pages, 11 figures, (dvi file and figures combined into a uuencoded
compressed file), (We correct an error in eq. 39 and its associated figure
(9). No changes at all to the text.), McGill-93/40, UQAM-PHE-93/03,
NEIPH-93-00
Extracting W Boson Couplings from the Production of Four Leptons
We consider the processes , including all possible charged lepton combinations, with
regard to measuring parameters characterizing the boson. We calculate at
what level these processes can be used to measure anamolous triple-boson
vertice coupling parameters for the cases of colliders at 500
and 1 center of mass energies.Comment: 13 pages,OCIP/C-93-
QCD Corrections to Associated Higgs Boson-Heavy Quark Production
We compute the O(alpha_s) QCD corrections to the inclusive process e^+e^- -->
t \bar t h. Although the total rate is small, it has a distinctive experimental
signature and can potentially be used to measure the top quark-Higgs boson
Yukawa coupling. The QCD corrections increase the rate by a factor of roughly
1.5 for e^+e^- --> t \bar t h at sqrt(s)=500 GeV and Mh=100 GeV. At sqrt(s)=1
TeV, the corrections are small.Comment: 18 pages, 11 figures, version to appear in Phys. Rev.
Studies for a Photon Collider at the ILC
One option at the International Linear Collider is to convert the electron
beams into high energy photon beams by Compton scattering a few millimetres in
front of the interaction region. Selected physics channels for this option have
been analysed and technical issues have been studied. So far no showstoppers
for this option have been found.Comment: V2: Minor changes, accepted by NI
Large Electric Dipole Moments of Heavy Neutrinos
In many models of CP violation, the electric dipole moment (EDM) of a heavy
charged or neutral lepton could be very large. We present an explicit model in
which a heavy neutrino EDM can be as large as e-cm, or even a factor
of ten larger if fine-tuning is allowed, and use an effective field theory
argument to show that this result is fairly robust. We then look at the
production cross section for these neutrinos, and by rederiving the Bethe-Block
formula, show that they could leave an ionization track. It is then noted that
the first signature of heavy neutrinos with a large EDM would come from
, leading to a very large rate for single photon plus
missing energy events, and the rate and angular distribution are found.
Finally, we look at some astrophysical consequences, including whether these
neutrinos could constitute the UHE cosmic rays and whether their decays in the
early universe could generate a net lepton asymmetry.Comment: 22 pages, 9 figure
- âŠ