183 research outputs found
Tau weak dipole moments from azimuthal asymmetries
We show that transverse and normal single- polarization of pairs
produced at unpolarized collisions, at the peak, are sensitive
to weak (magnetic and electric) dipole moments of the . We also show how
these components of the polarization are accessible by measuring
appropriate azimuthal asymmetries in the angular distribution of its decay
products. Sensitivities of the order of , for the
weak-electric dipole moment, and (), for the real
(imaginary) part of the weak-magnetic dipole moment of , may be achieved.
Compatible bounds are also presented from spin-spin correlated asymmetries.Comment: Talk given at the TAU'98 Workshop, September 1998, Santander, Spain.
8 pages, 2 figure
Electric polarizability of nuclei from a longitudinal sum rule
The nuclear electric polarizability is theoretically analyzed using a sum
rule derived from the longitudinal part of the forward Compton amplitude.
Beyond the leading dipole contribution, this approach leads to the presence of
potential-dependent terms that do not show up in previous analyses. The
significance of these new contributions is illustrated by performing an
explicit calculation for a proton-neutron system interacting via a separable
potential.Comment: 9 pages, revtex. Minor changes, two references added. To appear in
Nucl. Phys.
Universality-Breaking Effects in Leptonic Z Decays
We analyze the possibility of universality violation in diagonal leptonic
decays of the boson, in the context of interfamily "see-saw" models. In a
minimal extension of the Standard Model with right-handed neutrino fields, we
find that universality-breaking effects increase quadratically with the heavy
Majorana neutrino mass and may be observed in the running experiments.Comment: MZ-TH/93-04 #, LaTeX, 14 p. (2 Figs
Orbital phase resolved spectroscopy of 4U1538-52 with MAXI
4U 1538-52, an absorbed high mass X-ray binary with an orbital period of 3.73
days, shows moderate orbital intensity modulations with a low level of counts
during the eclipse. Several models have been proposed to explain the accretion
at different orbital phases by a spherically symmetric stellar wind from the
companion. The aim of this work is to study both the light curve and orbital
phase spectroscopy of this source in the long term. Particularly, the folded
light curve and the changes of the spectral parameters with orbital phase to
analyse the stellar wind of QV Nor, the mass donor of this binary system. We
used all the observations made from the Gas Slit Camera on board MAXI of 4U
1538-52 covering many orbits continuously. We obtained the good interval times
for every orbital phase range which were the input to extract our data. We
estimated the orbital period of the system and then folded the light curves and
we fitted the X-ray spectra with the same model for every orbital phase
spectrum. We also extracted the averaged spectrum of all the MAXI data
available. The MAXI spectra in the 2-20 keV energy range were fitted with an
absorbed Comptonization of cool photons on hot electrons. We found a strong
orbital dependence of the absorption column density but neither the
fluorescence iron emission line nor low energy excess were needed to fit the
MAXI spectra. The variation of the spectral parameters over the binary orbit
were used to examine the mode of accretion onto the neutron star in 4U 1538-52.
We deduce a best value of for QV Nor.Comment: 12 pages, 5 figures, accepted to be published by A&A, corrected typos
(changing bold font to normal one
WEAK DIPOLE MOMENTS AT COLLIDERS
The weak dipole moments of leptons and quarks, \ie those related to their
--coupling, are reviewed. Standard Model predictions and experimental
results may result in a stringent test for both their pointlike structure and
also for the Standard Model. Special attention is devoted to the anomalous
weak--magnetic dipole moment and to the --violating weak--electric dipole
moment.Comment: Latex file and 2 figures included in an uucoded compressed postscript
file. To appear in the proceedings of the Ringberg Workshop on "Perspectives
for electroweak interactions in collisions" hosted by the Max Planck
Institut, at the Ringberg Castle, M\"unich, February 5-8, 1995. Edited by B.
Knieh
Some constraints on neutral heavy leptons from flavor-conserving decays of the Z boson
Small neutrino masses can arise in some grand unified models or superstring
theories. We consider a model with an enhanced fermion sector containing Dirac
neutral heavy leptons. The dependence on the mass and mixing parameters of
these new fermions is investigated for several measurable quantities. We study
the flavor-conserving leptonic decays of the Z boson and universality breaking
in these decays. We also consider the W boson mass dependence on neutral heavy
lepton parameters.Comment: 20 pages, Revtex 3.0, 6 uuencoded and compressed postscript figures
included. Compressed postscript file of paper, including figures, also
available by anonymous ftp at
ftp://ftp.physics.carleton.ca/pub/theory/gour/ocipc9411.ps.Z . Accepted for
publication in Phys. Rev. D
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