88 research outputs found
Limits on excited tau leptons masses from leptonic tau decays
We study the effects induced by excited leptons on the leptonic tau decay at
one loop level. Using a general effective lagrangian approach to describe the
couplings of the excited leptons, we compute their contributions to the
leptonic decays and use the current experimental values of the branching ratios
to put limits on the mass of excited states and the substructure scale.Comment: 10 pages, 6 figures, to be published in Phys. Rev.
New Physics Potential with a Neutrino Telescope
Active Galactic Nuclei are considered as sources of neutrinos, with neutrino
energies extending up to 10^{18} eV. It is expected that these highly energetic
cosmic neutrinos will be detected by the neutrino telescopes, presently under
construction. The detection process is very sensitive to the total muon
neutrino cross-section. We examine how the total cross section changes at high
energies, by the single production of excited fermions (excited muon and
muon-neutrino). For parameters (masses, couplings) of the excited fermions
allowed by the experimental constraints, we find that for energies of the
incoming muon-neutrino above 100 TeV the cross-section for single production of
(excited muon and muon-neutrino) supersedes the standard total cross-section.Comment: 12 pages and 2 figures; typset using revtex; postscript files for the
figures provide
Sneutrino-induced like sign dilepton signal with conserved R-parity
Lepton number violation could be manifest in the sneutrino sector of
supersymmetric extensions of the standard model with conserved R-parity. Then
sneutrinos decay partly into the ``wrong sign charged lepton'' final state, if
kinematically accessible. In sneutrino pair production or associated single
sneutrino production, the signal then is a like sign dilepton final state.
Under favourable circumstances, such a signal could be visible at the LHC or a
next generation linear collider for a relative sneutrino mass-splitting of
order and sneutrino width of order (1 GeV). On the
other hand, the like sign dilepton event rate at the TEVATRON is probably too
small to be observable.Comment: 19 pages, 14 Figures. Section about LSD at LHC and TEVATRON added.
Previous Title "Single sneutrino production and the wrong charged lepton
signal
Strange Star Heating Events as a Model for Giant Flares of Soft Gamma-ray Repeaters
Two giant flares were observed on 5 March 1979 and 27 August 1998 from the
soft gamma-ray repeaters SGR 0526-66 and SGR 1900+14, respectively. The
striking similarity between these remarkable bursts strongly implies a common
nature. We show that the light curves of the giant bursts may be easily
explained in the model where the burst radiation is produced by the bare quark
surface of a strange star heated, for example, by impact of a massive
comet-like object.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Letter
Naturalness Bounds on Dipole Moments from New Physics
Assuming naturalness that the quantum corrections to the mass should not
exceed the order of the observed mass, we derive and apply model-independent
bounds on the anomalous magnetic moments and electric dipole moments of leptons
and quarks due to new physics.Comment: 4 pages, 2 figure
Model of the Quark Mixing Matrix
The structure of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is analyzed from
the standpoint of a composite model. A model is constructed with three families
of quarks, by taking tensor products of sufficient numbers of spin-1/2
representations and imagining the dominant terms in the mass matrix to arise
from spin-spin interactions. Generic results then obtained include the familiar
relation , and a less frequently
seen relation . The magnitudes of
and come out naturally to be of the right order. The phase in
the CKM matrix can be put in by hand, but its origin remains obscure.Comment: Presented by Mihir P. Worah at DPF 92 Meeting, Fermilab, November,
1992. 3 pages, LaTeX fil
Discriminating New Physics Scenarios at NLC: The Role of Polarization
We explore the potential of the Next Linear Collider (NLC), operating in the
mode, to disentangle new physics scenarios on single production.
We study the effects related with the exchange of composite fermion in the
reaction , and compare with those arising from trilinear
gauge boson anomalous couplings. We stress the role played by the initial state
polarization to increase the reach of this machine and to discriminate the
possible origin of the new phenomena.Comment: 26 pages, LaTeX file using ReVTeX. 10 Figure
Production in Two-Photon Processes at TRISTAN
We have carried out an inclusive measurement of production
in two-photon processes at TRISTAN. The mean was 58 GeV and the
integrated luminosity was 199 pb. High-statistics samples were
obtained under such conditions as no-, anti-electron, and remnant-jet tags. The
remnant-jet tag, in particular, allowed us, for the first time, to measure the
cross sections separately for the resolved-photon and direct processes.Comment: 20 pages, Latex format, 4 figures and KEK-mark included. Table 1
revised. To be published in Phys. Lett.
QCD corrections to decay-lepton polar and azimuthal angular distributions in e+e- -> t tbar in the soft-gluon approximation
QCD corrections to order alpha_s in the soft-gluon approximation to angular
distributions of decay charged leptons in the process e+e- -> t tbar followed
by semileptonic decay of t or tbar, are obtained in the e+e- centre-of-mass
frame. As compared to distributions in the top rest frame, these have the
advantage that they would allow direct comparison with experiment without the
need to reconstruct the top rest frame. The results also do not depend on the
choice of a spin quantization axis for t or tbar. Analytic expression for the
triple distribution in the polar angle of t and polar and azimuthal angles of
the lepton is obtained. Analytic expression is also derived for the
distribution in the charged-lepton polar angle. Numerical values are discussed
for total c.m. energies of 400 GeV, 800 GeV and 1500 GeV.Comment: 21 pages, Latex, 6 figures included in the submission. To appear in
Pramana - Journal of Physics; expanded version of hep-ph/0011321, v
Measurement of inclusive electron cross section in collisions at TRISTAN
We have studied open charm production in collisions with the
TOPAZ detector at the TRISTAN collider. In this study, charm
quarks were identified by electrons (and positrons) from semi-leptonic decays
of charmed hadrons. The data corresponded to an integrated luminosity of 95.3
pb at a center-of-mass energy of 58 GeV. The results are presented as
the cross sections of inclusive electron production in
collisions with an anti-tag condition, as well as the subprocess cross
sections, which correspond to resolved-photon processes. The latter were
measured by using a sub-sample with remnant jets. A comparison with various
theoretical predictions based on direct and resolved-photon processes showed
that our data prefer that with relatively large gluon contents in a photon at
small , with the next-to-leading order correction, and with a
charm-quark mass of 1.3 GeV.Comment: 26 pages, Latex format (article), 5 figures included, to be published
in Phys. Lett.
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