1,321 research outputs found
Addendum to "Coherent radio pulses from GEANT generated electromagnetic showers in ice"
We reevaluate our published calculations of electromagnetic showers generated
by GEANT 3.21 and the radio frequency pulses they produce in ice. We are
prompted by a recent report showing that GEANT 3.21-modeled showers are
sensitive to internal settings in the electron tracking subroutine. We report
the shower and pulse characteristics obtained with different settings of GEANT
3.21 and with GEANT 4. The default setting of electron tracking in GEANT 3.21
we used in previous work speeds up the shower simulation at the cost of
information near the end of the tracks. We find that settings tracking electron
and positron to lower energy yield a more accurate calculation, a more intense
shower, and proportionately stronger radio pulses at low frequencies. At high
frequencies the relation between shower tracking algorithm and pulse spectrum
is more complex. We obtain radial distributions of shower particles and phase
distributions of pulses from 100 GeV showers that are consistent with our
published results.Comment: 4 pages, 3 figure
Indication of Anisotropy in Electromagnetic Propagation over Cosmological Distances
We report a systematic rotation of the plane of polarization of
electromagnetic radiation propagating over cosmological distances. The effect
is extracted independently from Faraday rotation, and found to be correlated
with the angular positions and distances to the sources. Monte Carlo analysis
yields probabilistic P-values of order 10^(-3) for this to occur as a
fluctuation. A fit yields a birefringence scale of order 10^(25) meters.
Dependence on redshift z rules out a local effect. Barring hidden systematic
bias in the data, the correlation indicates a new cosmological effect.Comment: 5 pages, 1 figure, ReVTeX. For more information, see
http://www.cc.rochester.edu/college/rtc/Borge/aniso.htm
Soffer's inequality and the transversely polarized Drell-Yan process at next-to-leading order
We check numerically if Soffer's inequality for quark distributions is
preserved by next-to-leading order QCD evolution. Assuming that the inequality
is saturated at a low hadronic scale we estimate the maximal transverse double
spin asymmetry for Drell-Yan muon pair production to next-to-leading order
accuracy.Comment: 20 Pages, LaTeX, 7 figures as eps file
Stationary Distribution and Eigenvalues for a de Bruijn Process
We define a de Bruijn process with parameters n and L as a certain
continuous-time Markov chain on the de Bruijn graph with words of length L over
an n-letter alphabet as vertices. We determine explicitly its steady state
distribution and its characteristic polynomial, which turns out to decompose
into linear factors. In addition, we examine the stationary state of two
specializations in detail. In the first one, the de Bruijn-Bernoulli process,
this is a product measure. In the second one, the Skin-deep de Bruin process,
the distribution has constant density but nontrivial correlation functions. The
two point correlation function is determined using generating function
techniques.Comment: Dedicated to Herb Wilf on the occasion of his 80th birthda
Next-to-leading Order Evolution of Transversity Distributions and Soffer's Inequality
We present a calculation of the two-loop splitting functions for the
evolution of the twist-2 `transversity' parton densities of transversely
polarized nucleons. We study the implications of our results for Soffer's
inequality for the case of valence quark densities.Comment: 23 Pages, LaTeX, 2 figures as eps files, final, slightly modified
version, to appear in Phys. Rev.
Multiple-Scattering Series For Color Transparency
Color transparency CT depends on the formation of a wavepacket of small
spatial extent. It is useful to interpret experimental searches for CT with a
multiple scattering scattering series based on wavepacket-nucleon scattering
instead of the standard one using nucleon-nucleon scattering. We develop
several new techniques which are valid for differing ranges of energy. These
techniques are applied to verify some early approximations; study new forms of
the wave-packet-nucleon interaction; examine effects of treating wave packets
of non-zero size; and predict the production of 's in electron scattering
experiments.Comment: 26 pages, U.Wa. preprint 40427-23-N9
Management of Glucocorticoid-Induced Osteoporosis
This review summarizes the available evidence-based data that form the basis for therapeutic intervention and covers the current status of glucocorticoid-induced osteoporosis (GIOP) management, regulatory requirements, and risk-assessment options. Glucocorticoids are known to cause bone loss and fractures, yet many patients receiving or initiating glucocorticoid therapy are not appropriately evaluated and treated. An European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis workshop was convened to discuss GIOP management and to provide a report by a panel of experts. An expert panel reviewed the available studies that discussed approved therapeutic agents, focusing on randomized and controlled clinical trials reporting on bone mineral density and/or fracture risk of at least 48weeks' duration. There is no evidence that GIOP and postmenopausal osteoporosis respond differently to treatments. The FRAX algorithm can be adjusted according to glucocorticoid dose. Available antiosteoporotic therapies such as bisphosphonates and teriparatide are efficacious in GIOP management. Several other agents approved for the treatment of postmenopausal osteoporosis may become available for GIOP. It is advised to stop antiosteoporotic treatment after glucocorticoid cessation, unless the patient remains at increased risk of fracture. Calcium and vitamin D supplementation as an osteoporosis-prevention measure is less effective than specific antiosteoporotic treatment. Fracture end-point studies and additional studies investigating specific subpopulations (pediatric, premenopausal, or elderly patients) would strengthen the evidence base and facilitate the development of intervention thresholds and treatment guideline
Next-to-leading order Q^2-evolution of the transversity distribution h_1(x, Q^2)
We present a calculation of the two-loop anomalous dimension for the
transversity distribution h_1(x,Q^2), , in the MS scheme of
the dimensional regularization. Due to the chiral-odd nature, h_1 does not mix
with the gluon distributions, and thus our result is the same for the
flavor-singlet and nonsinglet distributions. At small n (moment of h_1),
is significantly larger than (the anomalous
dimension for the nonsinglet f_1), but approaches very
quickly at large n, keeping the relation .
This feature is in parallel to the relation between the one-loop anomalous
dimension for f_1 and h_1.Comment: 28 pages, Latex. 10 figures. Submitted for publication some time ag
In-medium Yang-Mills equations: a derivation and canonical quantization
The equations for Yang-Mills field in a medium are derived in a linear
approximation with respect to the gauge coupling parameter and the external
field. The obtained equations closely resemble the macroscopic Maxwell
equations. A canonical quantization is performed for a family of Fermi-like
gauges in the case of constant and diagonal (in the group indices) tensors of
electric permittivity and magnetic permeability. The physical subspace is
defined and the gauge field propagator is evaluated for a particular choice of
the gauge. The propagator is applied for evaluation of the cross-section of
ellastic quark scattering in the Born approximation. Possible applications to
Cherenkov-type gluon radiation are commented briefly.Comment: 27 pages, references added, version extended with emphasis on
non-Abelian gauge group impact on medium characteristics. To appear in J.
Phys.
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