471 research outputs found
Q^2 dependence of diffractive vector meson electroproduction
We give a general formula for the cross section for diffractive vector meson
electroproduction, gamma^* p -> Vp. We first calculate diffractive qqbar
production, and then use parton-hadron duality by projecting out the J^P = 1^-
state in the appropriate mass interval. We compare the Q^2 dependence of the
cross section for the diffractive production of rho and J/psi mesons with
recent HERA data. We include the characteristic Q^2 dependence associated with
the use of the skewed gluon distribution. We give predictions for
sigma_L/sigma_T for both rho and J/psi production.Comment: 15 pages, LaTeX, including five PostScript figure
Transport properties of heterogeneous materials derived from Gaussian random fields: Bounds and Simulation
We investigate the effective conductivity () of a class of
amorphous media defined by the level-cut of a Gaussian random field. The three
point solid-solid correlation function is derived and utilised in the
evaluation of the Beran-Milton bounds. Simulations are used to calculate
for a variety of fields and volume fractions at several different
conductivity contrasts. Relatively large differences in are observed
between the Gaussian media and the identical overlapping sphere model used
previously as a `model' amorphous medium. In contrast shows little
variability between different Gaussian media.Comment: 15 pages, 14 figure
Top quark physics in hadron collisions
The top quark is the heaviest elementary particle observed to date. Its large
mass makes the top quark an ideal laboratory to test predictions of
perturbation theory concerning heavy quark production at hadron colliders. The
top quark is also a powerful probe for new phenomena beyond the Standard Model
of particle physics. In addition, the top quark mass is a crucial parameter for
scrutinizing the Standard Model in electroweak precision tests and for
predicting the mass of the yet unobserved Higgs boson. Ten years after the
discovery of the top quark at the Fermilab Tevatron top quark physics has
entered an era where detailed measurements of top quark properties are
undertaken. In this review article an introduction to the phenomenology of top
quark production in hadron collisions is given, the lessons learned in Tevatron
Run I are summarized, and first Run II results are discussed. A brief outlook
to the possibilities of top quark research a the Large Hadron Collider,
currently under construction at CERN, is included.Comment: 84 pages, 32 figures, accepted for publication by Reports on Progress
in Physic
Direct versus indirect detection in mSUGRA with self-consistent halo models
We perform a detailed analysis of the detection prospects of neutralino dark
matter in the mSUGRA framework. We focus on models with a thermal relic
density, estimated with high accuracy using the DarkSUSY package, in the range
favored by current precision cosmological measurements. Direct and indirect
detection rates are computed implementing two models for the dark matter halo,
tracing opposite regimes for the phase of baryon infall, with fully consistent
density profiles and velocity distribution functions. This has allowed, for the
first time, a fully consistent comparison between direct and indirect detection
prospects. We discuss all relevant regimes in the mSUGRA parameter space,
underlining relevant effects, and providing the basis for extending the
discussion to alternative frameworks. In general, we find that direct detection
and searches for antideuterons in the cosmic rays seems to be the most
promising ways to search for neutralinos in these scenarios.Comment: 26 pages, 9 figure
Theory of laser ion acceleration from a foil target of nanometers
A theory for laser ion acceleration is presented to evaluate the maximum ion
energy in the interaction of ultrahigh contrast (UHC) intense laser with a
nanometer-scale foil. In this regime the energy of ions may be directly related
to the laser intensity and subsequent electron dynamics. This leads to a simple
analytical expression for the ion energy gain under the laser irradiation of
thin targets. Significantly, higher energies for thin targets than for thicker
targets are predicted. Theory is concretized to the details of recent
experiments which may find its way to compare with these results.Comment: 22 pages 7 figures. will be submitted to NJ
Heavy Quarkonium Physics
This report is the result of the collaboration and research effort of the
Quarkonium Working Group over the last three years. It provides a comprehensive
overview of the state of the art in heavy-quarkonium theory and experiment,
covering quarkonium spectroscopy, decay, and production, the determination of
QCD parameters from quarkonium observables, quarkonia in media, and the effects
on quarkonia of physics beyond the Standard Model. An introduction to common
theoretical and experimental tools is included. Future opportunities for
research in quarkonium physics are also discussed.Comment: xviii + 487 pages, 260 figures. The full text is also available at
the Quarkonium Working Group web page: http://www.qwg.to.infn.i
TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider
The TESLA Technical Design Report Part III: Physics at an e+e- Linear
ColliderComment: 192 pages, 131 figures. Some figures have reduced quality. Full
quality figures can be obtained from http://tesla.desy.de/tdr. Editors -
R.-D. Heuer, D.J. Miller, F. Richard, P.M. Zerwa
Structure-property correlations in model composite materials
We investigate the effective properties (conductivity, diffusivity and elastic moduli) of model random composite media derived from Gaussian random fields and overlapping hollow spheres. The morphologies generated in the models exhibit low percolation thresholds and give a realistic representation of the complex microstructure observed in many classes of composites. The statistical correlation functions of the models are derived and used to evaluate rigorous bounds on each property. Simulation of the effective conductivity is used to demonstrate the applicability of the bounds. The key morphological features which effect composite properties are discussed
Galactic-Centre Gamma Rays in CMSSM Dark Matter Scenarios
We study the production of gamma rays via LSP annihilations in the core of
the Galaxy as a possible experimental signature of the constrained minimal
supersymmetric extension of the Standard Model (CMSSM), in which
supersymmetry-breaking parameters are assumed to be universal at the GUT scale,
assuming also that the LSP is the lightest neutralino chi. The part of the
CMSSM parameter space that is compatible with the measured astrophysical
density of cold dark matter is known to include a stau_1 - chi coannihilation
strip, a focus-point strip where chi has an enhanced Higgsino component, and a
funnel at large tanb where the annihilation rate is enhanced by the poles of
nearby heavy MSSM Higgs bosons, A/H. We calculate the total annihilation rates,
the fractions of annihilations into different Standard Model final states and
the resulting fluxes of gamma rays for CMSSM scenarios along these strips. We
observe that typical annihilation rates are much smaller in the coannihilation
strip for tanb = 10 than along the focus-point strip or for tanb = 55, and that
the annihilation branching ratios differ greatly between the different dark
matter strips. Whereas the current Fermi-LAT data are not sensitive to any of
the CMSSM scenarios studied, and the calculated gamma-ray fluxes are probably
unobservably low along the coannihilation strip for tanb = 10, we find that
substantial portions of the focus-point strips and rapid-annihilation funnel
regions could be pressured by several more years of Fermi-LAT data, if
understanding of the astrophysical background and/or systematic uncertainties
can be improved in parallel.Comment: 33 pages, 12 figures, comments and references added, version to
appear in JCA
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