178 research outputs found
Photon-Photon and Pomeron-Pomeron Processes in Peripheral Heavy Ion Collisions
We estimate the cross sections for the production of resonances, pion pairs
and a central cluster of hadrons in peripheral heavy-ion collisions through
two-photon and double-pomeron exchange, at energies that will be available at
RHIC and LHC. The effect of the impact parameter in the diffractive reactions
is introduced, and imposing the condition for realistic peripheral collisions
we verify that in the case of very heavy ions the pomeron-pomeron contribution
is indeed smaller than the electromagnetic one. However, they give a
non-negligible background in the collision of light ions. This diffractive
background will be more important at RHIC than at LHC.Comment: 22 pages, 1 Postscript figures, 4 tables, to appear in Phys. Rev.
Dicyclic Horizontal Symmetry and Supersymmetric Grand Unification
It is shown how to use as horizontal symmetry the dicyclic group in a supersymmetric unification where
one acts on the first and second families, in a horizontal doublet, and
the other acts on the third. This can lead to acceptable quark masses and
mixings, with an economic choice of matter supermultiplets, and charged lepton
masses can be accommodated.Comment: 10 pages, LaTe
Quark Mass Textures Within a Finite Non-Abelian Dicyclic Group
Using as a flavor symmetry a finite nonabelian dicyclic group, we
show how to derive quark mass matrices with two arrangements of symmetric
texture zeros which are phenomenologically viable. Three other such acceptable
textures in the recent literature are unattainable in this approach and hence
disfavored. We assume massive vector-like fermions and Higgs singlets
transforming as judiciously-chosen doublets and use the tree-level
mass generation mechanism of Froggatt and Nielsen.Comment: 11 pages latex including two figures. published version. New title.
Slight modificatio
Exclusive Production of Higgs Bosons in Hadron Colliders
We study the exclusive, double--diffractive production of the Standard Model
Higgs particle in hadronic collisions at LHC and FNAL (upgraded) energies. Such
a mechanism would provide an exceptionally clean signal for experimental
detection in which the usual penalty for triggering on the rare decays of the
Higgs could be avoided. In addition, because of the color singlet nature of the
hard interaction, factorization is expected to be preserved, allowing the
cross--section to be related to similar hard--diffractive events at HERA.
Starting from a Fock state expansion in perturbative QCD, we obtain an estimate
for the cross section in terms of the gluon structure functions squared of the
colliding hadrons. Unfortunately, our estimates yield a production rate well
below what is likely to be experimentally feasible.Comment: 17 pages, RevTeX file, four uufiled PostScript figures. UMPP #94-177.
(Revised version. Some mistakenly missing Feynman diagrams are now added.
Results do not change qualitatively. Paper reorganized.
Horizontal Symmetry for Quark and Squark Masses in Supersymmetric SU(5)
Recent interest in horizontal symmetry model building has been driven mainly
by the large top mass and hence strong hierarchy in quark masses, and the
possibility of appropriately constrained soft squark mass matrices, in place of
an assumed universality condition, for satisfying the relevant FCNC
constraints. Here we present the first successful SUSY- model that has
such a feature. The horizontal symmetry is a gauged
(). All nonrenormalizable terms compatible with
the symmetry are allowed in the mass matrix constructions. Charged lepton
masses can also be accommodated.Comment: 15 pages, latex, 1 latex figure included version to be published in
Phys. Rev. Lett. ; some small changes in notations and presentation, a small
paragragh and 3 references adde
Heavy neutrino threshold effects in low energy phenomenology
Right handed neutrinos with mass of GeV are
required to implement the see-saw mechanism and generate neutrino masses
capable of playing a role in structure formation.
Moreover models of fermion masses often relate the Yukawa couplings involving
these neutrinos to the up-quark Yukawa couplings. Here we study the effects of
such couplings on the radiative corrections to quark masses. We find that
equality at may still give the correct --
ratio at low energies, but only if there is large mixing in the
charged leptonic sector. We propose specific mass matrix ``textures'' dictated
by a family symmetry whose structure preserves at
. In these schemes, due to the large mixing,
it is possible to give a simultaneous solution to the solar neutrino deficit
and the atmospheric neutrino problem.Comment: 22 pages, latex file, including 8 latex figures. Revised version
(typos corrected, references added), to be published in Nucl. Phys.
Neutrino Oscillations from Discrete Non-Abelian Symmetries
I discuss a SUSY-GUT model with a non-Abelian discrete family symmetry that
explains the observed hierarchical pattern of quark and lepton masses. This
model predicts modified quadratic seesaw neutrino
masses and mixing angles which are interesting for three reasons: i.) they
offer a solution to the solar neutrino problem, ii.) the tau neutrino has the
right mass for a cosmologically interesting hot dark matter candidate, and
iii.) they suggest a positive result for the
oscillation searches by the CHORUS and NOMAD collaborations. However, the model
shares some problems with many other predictive GUT models of quark and lepton
masses. Well-known and once successful mass and angle relations, such as the
relation , are found to be in
conflict with the current experimental status. Attempts to correct these
relations seem to lead to rather contrived models.Comment: 16 pages, uses harvmac, epsf, tables, 4 figure
Social innovations for social cohesion in Western Europe: success dimensions for lifelong learning and education
YesIn addressing the EU2020 goals, skills shortage combined with increasing unemployment rates is to be primarily tackled in Western Europe; the common factor here is education. Education and lifelong learning (LL) are the key strands governing employability in the European labour market. Overarching concepts capable of addressing social challenges within education and LL that contribute towards better practices are seen as social innovations (SI). While SI in education is well founded in the developing countries, Europe is still in the process of gaining progressive momentum in this direction. In addressing various societal challenges, this study looks at observable trends in SI for education across Western Europe. About 30 innovations have been recorded across 11 countries that are essentially focussed on: social integration, alternative/new forms of education, digital learning, new learning arrangements, new LL strategies, early career planning, youth employment, quality improvements and new education standards, transition management, and entrepreneurial education.European Union’s Seventh Framework Programme for research, technological development and demonstration [grant number 612870]
High-E_T dijet photoproduction at HERA
The cross section for high-E_T dijet production in photoproduction has been
measured with the ZEUS detector at HERA using an integrated luminosity of 81.8
pb-1. The events were required to have a virtuality of the incoming photon,
Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the
range 142 < W < 293 GeV. Events were selected if at least two jets satisfied
the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV
and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of
the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to
the parton distributions in the photon and proton and effects beyond
next-to-leading order in QCD. Hence these data can be used to constrain further
the parton densities in the proton and photon.Comment: 36 pages, 13 figures, 20 tables, including minor revisions from
referees. Accepted by Phys. Rev.
Measurement of (anti)deuteron and (anti)proton production in DIS at HERA
The first observation of (anti)deuterons in deep inelastic scattering at HERA
has been made with the ZEUS detector at a centre-of-mass energy of 300--318 GeV
using an integrated luminosity of 120 pb-1. The measurement was performed in
the central rapidity region for transverse momentum per unit of mass in the
range 0.3<p_T/M<0.7. The particle rates have been extracted and interpreted in
terms of the coalescence model. The (anti)deuteron production yield is smaller
than the (anti)proton yield by approximately three orders of magnitude,
consistent with the world measurements.Comment: 26 pages, 9 figures, 5 tables, submitted to Nucl. Phys.
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