3,799 research outputs found
THE SENSITIVITY TO NEW PHYSICS OF A LEP SCAN IN 1995
We study the implications of possible off-peak measurements in the 1995 LEP
run, in regard to probing physics beyond the Standard Model. To do so, we
determine the accuracy with which various nonstandard couplings can be expected
to be measured in the three different scan scenarios recently discussed by
Clarke and Wyatt. We find that each scan scenario allows greater sensitivity to
a different set of new physics couplings. Oblique parameters are best measured
with the longest scan, while nonstandard fermion couplings to the Z tend to be
better constrained (albeit only marginally) if all of the 1995 LEP measurements
are taken on the Z peak.Comment: Plain TeX, 9 pages, no figures. We have streamlined our presentation
by omitting observables of our Class B. All else is completely unchanged
Determination of alpha_s from scaling violations of truncated moments of structure functions
We determine the strong coupling alpha_s(M_Z) from scaling violations of
truncated moments of the nonsinglet deep inelastic structure function F_2.
Truncated moments are determined from BCDMS and NMC data using a neural network
parametrization which retains the full experimental information on errors and
correlations. Our method minimizes all sources of theoretical uncertainty and
bias which characterize extractions of alpha_s from scaling violations. We
obtain alpha_s(M_Z) = 0.124 +0.004-0.007 (exp.) + 0.003- 0.004 (th.).Comment: 24 pages, 4 figures, latex with epsfig; neural network
parametrization available from http://sophia.ecm.ub.es/f2neura
Heavy Quark Lifetimes, Mixing and CP Violation
This paper emphasizes four topics that represent some of the year's
highlights in heavy quark physics. First of all, a review is given of charm
lifetime measurements and how they lead to better understanding of the
mechanisms of charm decay. Secondly, the CLEO collaboration's new search for
charm mixing is reported, which significantly extends the search for new
physics in that sector. Thirdly, important updates in Bs mixing are summarized,
which result in a new limit on the mass difference, and which further constrain
the unitarity triangle. Finally, the first efforts to measure CP violation in
the B system are discussed. Results are shown for the CDF and ALEPH
measurements of sin(2beta), as well as the CLEO branching fraction measurements
of B-->Kpi,pipi, which have implications for future measurements of alpha.Comment: 25 pages, 15 figures. Talk given at the XIX International Symposium
on Lepton and Photon Interactions, Stanford University, August 9-14, 199
The Baffling Semileptonic Branching Ratio of Mesons
The apparent gap between the measured and the expected value for the
semileptonic branching ratio of mesons has become more serious over the
last year. This is due to the improved quality of the data and to the
increasing maturity of the theoretical treatment of non-perturbative
corrections. We discuss various theoretical options to reduce the semileptonic
branching ratio; among the more spectacular resolutions of the apparent
puzzle is the possibility of an unorthodox enhancement in non-perturbative
corrections or even of an intervention by `New Physics'. Phenomenological
implications of such scenarios are pointed out.Comment: 16 Latex pages; 4 figures to be obtained from I.Bigi; preprint
CERN-TH.7082/93; some misprints in the original version have been corrected
and some references adde
Comment on the recent COMPASS data on the spin structure function g_1
We examine the recent COMPASS data on the spin structure function g_1
singlet. We show that it is rather difficult to use the data in the present
form in order to draw conclusions on the initial parton densities. However, our
tentative estimate is that the data better agree with positive rather than
negative initial gluon densities.Comment: 8 pages, 1 figur
Ultraviolet Completion of Flavour Models
Effective Flavour Models do not address questions related to the nature of
the fundamental renormalisable theory at high energies. We study the
ultraviolet completion of Flavour Models, which in general has the advantage of
improving the predictivity of the effective models. In order to illustrate the
important features we provide minimal completions for two known A4 models. We
discuss the phenomenological implications of the explicit completions, such as
lepton flavour violating contributions that arise through the exchange of
messenger fields.Comment: 18 pages, 8 figure
The Inclusive Semileptonic Decay Lepton Spectrum from
In this talk, we review the QCD calculation of the lepton spectrum from
inclusive semileptonic decay. We compare this prediction to that of the
ACCMM model. This latter work was done in collaboration with Csaba Csaki.Comment: MIT-CTP-2333, uses LATEX. Invited Talk, Presented at WHEPP-3 Workshop
in Madras,India, January, 199
Polarized Deeply Inelastic Scattering (DIS) Structure Functions for Nucleons and Nuclei
We extract parton distribution functions (PDFs) and structure functions from
recent experimental data of polarized lepton-DIS on nucleons at next-to-leading
order (NLO) Quantum Chromodynamics. We apply the Jacobi polynomial method to
the DGLAP evolution as this is numerically efficient. Having determined the
polarized proton and neutron spin structure, we extend this analysis to
describe 3He and 3H polarized structure functions, as well as various sum
rules. We compare our results with other analyses from the literature.Comment: LaTeX, 12 pages, 11 figures, 6 tables. Update to match published
versio
Naturalness of nearly degenerate neutrinos
If neutrinos are to play a relevant cosmological role, they must be
essentially degenerate. We study whether radiative corrections can or cannot be
responsible for the small mass splittings, in agreement with all the available
experimental data. We perform an exhaustive exploration of the bimaximal mixing
scenario, finding that (i) the vacuum oscillations solution to the solar
neutrino problem is always excluded; (ii) if the mass matrix is produced by a
see-saw mechanism, there are large regions of the parameter space consistent
with the large angle MSW solution, providing a natural origin for the hierarchy; (iii) the bimaximal structure becomes
then stable under radiative corrections. We also provide analytical expressions
for the mass splittings and mixing angles and present a particularly simple
see-saw ansatz consistent with all observations.Comment: 25 pages, LaTeX, 6 ps figures, psfig.sty. Typos, references and minor
details corrected. Additional condition for the MSW mechanism incorporated.
New viable textures adde
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