615 research outputs found
Novel Transversity Properties in Semi-Inclusive Deep Inelastic Scattering
The -odd distribution functions contributing to transversity properties of
the nucleon and their role in fueling nontrivial contributions to azimuthal
asymmetries in semi-inclusive deep inelastic scattering are investigated. We
use a dynamical model to evaluate these quantities in terms of HERMES
kinematics.Comment: 5 pages revtex; 5 eps figures. References added. To appear as a Rapid
Communication in Physical Review
Spin Dependent Fragmentation Functions for Heavy Flavor Baryons and Single Heavy Hyperon Polarization
Spin dependent fragmentation functions for heavy flavor quarks to fragment
into heavy baryons are calculated in a quark-diquark model. The production of
intermediate spin 1/2 and 3/2 excited states is explicity included.
, and production rate and polarization at LEP energies are
calculated and, where possible, compared with experiment. A different approach,
also relying on a heavy quark-diquark model, is proposed for the small momentum
transfer inclusive production of polarized heavy flavor hyperons. The predicted
polarization is roughly in agreement with experiment.Comment: LaTeX2e 11 pages with 4 PostScript figures. To be published in
Proceedings of the International Workshop ``Symmetries and spin'',
Praha-SPIN-200
Branonium
We study the bound states of brane/antibrane systems by examining the motion
of a probe antibrane moving in the background fields of N source branes. The
classical system resembles the point-particle central force problem, and the
orbits can be solved by quadrature. Generically the antibrane has orbits which
are not closed on themselves. An important special case occurs for some
Dp-branes moving in three transverse dimensions, in which case the orbits may
be obtained in closed form, giving the standard conic sections but with a
nonstandard time evolution along the orbit. Somewhat surprisingly, in this case
the resulting elliptical orbits are exact solutions, and do not simply apply in
the limit of asymptotically-large separation or non-relativistic velocities.
The orbits eventually decay through the radiation of massless modes into the
bulk and onto the branes, and we estimate this decay time. Applications of
these orbits to cosmology are discussed in a companion paper.Comment: 34 pages, LaTeX, 4 figures, uses JHEP
D-Brane Chemistry
We study several different kinds of bound states built from D-branes and
orientifolds. These states are to atoms what branonium - the bound state of a
brane and its anti-brane - is to positronium, inasmuch as they typically
involve a light brane bound to a much heavier object with conserved charges
which forbid the system's decay. We find the fully relativistic motion of a
probe Dp'-brane in the presence of source Dp-branes is integrable by
quadratures. Keplerian conic sections are obtained for special choices for p
and p' and the systems are shown to be equivalent to nonrelativistic systems.
Their quantum behaviour is also equivalent to the corresponding
non-relativistic limit. In particular the p=6, p'=0 case is equivalent to a
non-relativistic dyon in a magnetic monopole background, with the trajectories
in the surface of a cone. We also show that the motion of the probe branes
about D6-branes in IIA theory is equivalent to the motion of the corresponding
probes in the uplift to M-theory in 11 dimensions, for which there are no
D6-branes but their fields are replaced by a particular Taub-NUT geometry. We
further discuss the interactions of D-branes and orientifold planes having the
same dimension. this system behaves at large distances as a brane-brane system
but at shorter distances it does not have the tachyon instability.Comment: ref. added and typos correcte
On the Path of a Quasi-static Crack in Mode III
A method for finding the path of a quasi-static crack growing in a brittle body is presented. The propagation process is modelled by a sequence of discrete steps optimizing the elastic energy released. An explicit relationship between the optimal growing direction and the parameters defining the local elastic field around the tip is obtained for an anti-plane field. This allows to describe a simple algorithm to compute the crack path
Covariant description of inelastic electron--deuteron scattering:predictions of the relativistic impulse approximation
Using the covariant spectator theory and the transversity formalism, the
unpolarized, coincidence cross section for deuteron electrodisintegration,
, is studied. The relativistic kinematics are reviewed, and simple
theoretical formulae for the relativistic impulse approximation (RIA) are
derived and discussed. Numerical predictions for the scattering in the high
region obtained from the RIA and five other approximations are presented
and compared. We conclude that measurements of the unpolarized coincidence
cross section and the asymmetry , to an accuracy that will distinguish
between different theoretical models, is feasible over most of the wide
kinematic range accessible at Jefferson Lab.Comment: 54 pages and 24 figure
Transversity distributions in the nucleon in the large-N_c limit
We compute the quark and antiquark transversity distributions in the nucleon
at a low normalization point of 600 MeV in the large- limit, where the
nucleon can be described as a soliton of an effective chiral theory (chiral
quark-soliton model). The flavor-nonsinglet distributions, and , appear in leading order
of the -expansion, while the flavor-singlet distributions, and , are non-zero only in
next-to-leading order. The transversity quark and antiquark distributions are
found to be significantly different from the longitudinally polarized
distributions and , respectively, in contrast to the prediction of the naive
non-relativistic quark model. We show that this affects the predictions for the
spin asymmetries in Drell-Yan pair production in transversely polarized pp and
ppbar collisions.Comment: 45 pages, 16 figure
Transverse Spin Structure of the Nucleon through Target Single Spin Asymmetry in Semi-Inclusive Deep-Inelastic Reaction at Jefferson Lab
Jefferson Lab (JLab) 12 GeV energy upgrade provides a golden opportunity to
perform precision studies of the transverse spin and
transverse-momentum-dependent structure in the valence quark region for both
the proton and the neutron. In this paper, we focus our discussion on a
recently approved experiment on the neutron as an example of the precision
studies planned at JLab. The new experiment will perform precision measurements
of target Single Spin Asymmetries (SSA) from semi-inclusive electro-production
of charged pions from a 40-cm long transversely polarized He target in
Deep-Inelastic-Scattering kinematics using 11 and 8.8 GeV electron beams. This
new coincidence experiment in Hall A will employ a newly proposed solenoid
spectrometer (SoLID). The large acceptance spectrometer and the high polarized
luminosity will provide precise 4-D (, , and ) data on the
Collins, Sivers, and pretzelocity asymmetries for the neutron through the
azimuthal angular dependence. The full 2 azimuthal angular coverage in the
lab is essential in controlling the systematic uncertainties. The results from
this experiment, when combined with the proton Collins asymmetry measurement
and the Collins fragmentation function determined from the ee collision
data, will allow for a quark flavor separation in order to achieve a
determination of the tensor charge of the d quark to a 10% accuracy. The
extracted Sivers and pretzelocity asymmetries will provide important
information to understand the correlations between the quark orbital angular
momentum and the nucleon spin and between the quark spin and nucleon spin.Comment: 23 pages, 13 figures, minor corrections, matches published versio
Electromagnetic form factors of the nucleon in a covariant diquark model
We present a simple covariant constituent diquark-quark model for the
nucleon. The nucleon is assumed to be composed of a scalar diquark and a quark
which interact via a quark exchange. Starting from the Bethe-Salpeter equation,
the instantaneous approximation leads to a diquark-quark Salpeter equation. In
the Mandelstam formalism, the electromagnetic form factors of the nucleon are
calculated for momentum transfers up to q^2 = - 3 \; (\mbox{GeV/c})^2. A
remarkable description of the experimental data is obtained. Especially, the
model gives nearly the right values for the proton and (negative) neutron
charge radii, and a qualitative description of the magnetic form factors.Comment: 17 pages, revtex, 8 figures in additional fil
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
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