23 research outputs found
Polarized structure functions of nucleons and nuclei
We determine the quark distributions and structure functions for both
unpolarized and polarized DIS of leptons on nucleons and nuclei. The scalar and
vector mean fields in the nucleus modify the motion of the quarks inside the
nucleons. By taking into account this medium modification, we are able to
reproduce the experimental data on the unpolarized EMC effect, and to make
predictions for the polarized EMC effect. We discuss examples of nuclei where
the polarized EMC effect could be measured. We finally present an extension of
our model to describe fragmentation functions.Comment: To appear in the proceedings of Quarks in Hadrons and Nuclei, Erice,
16-24 September 200
EMC and Polarized EMC Effects in Nuclei
We determine nuclear structure functions and quark distributions for Li,
B, N and Al. For the nucleon bound state we solve the
covariant quark-diquark equations in a confining Nambu--Jona-Lasinio model,
which yields excellent results for the free nucleon structure functions. The
nucleus is described using a relativistic shell model, including mean scalar
and vector fields that couple to the quarks in the nucleon. The nuclear
structure functions are then obtained as a convolution of the structure
function of the bound nucleon with the light-cone nucleon distributions. We
find that we are readily able to reproduce the EMC effect in finite nuclei and
confirm earlier nuclear matter studies that found a large polarized EMC effect.Comment: 8 pages, 9 figure
Nucleon quark distributions in a covariant quark-diquark model
Spin-dependent and spin-independent quark light-cone momentum distributions
and structure functions are calculated for the nucleon. We utilize a modified
Nambu-Jona-Lasinio model in which confinement is simulated by eliminating
unphysical thresholds for nucleon decay into quarks. The nucleon bound state is
obtained by solving the Faddeev equation in the quark-diquark approximation,
where both scalar and axial-vector diquark channels are included. We find
excellent agreement between our model results and empirical data.Comment: 6 pages, 7 figure
Quark distributions in nucleons and nuclei
Parallel Session B Light QuarksWe discuss the medium modifications of quark distributions and structure functions in the framework of a chiral effective quark theory. Particular emphasis is put on the isospin dependence of the in-medium quark distributions. As an interesting application, we discuss a possible solution of the so called NuTeV anomaly. Possible extensions of the model to describe fragmentation functions are also discussed.Wolfgang Bentz, Ian C. Cloët, Takuya Ito, Anthony W. Thomas, K. Yazak
Reassessment of the NuTeV determination of the Weinberg angle
In light of the recent discovery of the importance of the isovector EMC
effect for the interpretation of the NuTeV determination of sin^2 theta_W, it
seems timely to reassess the central value and the errors on this fundamental
Standard Model parameter derived from the NuTeV data. We also include earlier
work on charge symmetry violation and the recent limits on a possible asymmetry
between s and \bar{s} quarks. With these corrections we find a revised NuTeV
result of sin^2 theta_W = 0.2232 \pm 0.0013(stat) \pm 0.0024(syst), which is in
excellent agreement with the running of sin^2 theta_W predicted by the Standard
Model.Comment: 4 pages, one figur
Masses of ground and excited-state hadrons
We present the first Dyson-Schwinger equation calculation of the light hadron
spectrum that simultaneously correlates the masses of meson and baryon ground-
and excited-states within a single framework. At the core of our analysis is a
symmetry-preserving treatment of a vector-vector contact interaction. In
comparison with relevant quantities the
root-mean-square-relative-error/degree-of freedom is 13%. Notable amongst our
results is agreement between the computed baryon masses and the bare masses
employed in modern dynamical coupled-channels models of pion-nucleon reactions.
Our analysis provides insight into numerous aspects of baryon structure; e.g.,
relationships between the nucleon and Delta masses and those of the
dressed-quark and diquark correlations they contain.Comment: 25 pages, 7 figures, 4 table
Survey of nucleon electromagnetic form factors
A dressed-quark core contribution to nucleon electromagnetic form factors is
calculated. It is defined by the solution of a Poincare' covariant Faddeev
equation in which dressed-quarks provide the elementary degree of freedom and
correlations between them are expressed via diquarks. The nucleon-photon vertex
involves a single parameter; i.e., a diquark charge radius. It is argued to be
commensurate with the pion's charge radius. A comprehensive analysis and
explanation of the form factors is built upon this foundation. A particular
feature of the study is a separation of form factor contributions into those
from different diagram types and correlation sectors, and subsequently a
flavour separation for each of these. Amongst the extensive body of results
that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of
axial-vector quark-quark correlations; and for both the neutron and proton the
ratio of Sachs electric and magnetic form factors possesses a zero.Comment: 43 pages, 17 figures, 12 tables, 5 appendice
State sampling dependence of the Hopfield network inference
The fully connected Hopfield network is inferred based on observed
magnetizations and pairwise correlations. We present the system in the glassy
phase with low temperature and high memory load. We find that the inference
error is very sensitive to the form of state sampling. When a single state is
sampled to compute magnetizations and correlations, the inference error is
almost indistinguishable irrespective of the sampled state. However, the error
can be greatly reduced if the data is collected with state transitions. Our
result holds for different disorder samples and accounts for the previously
observed large fluctuations of inference error at low temperatures.Comment: 4 pages, 1 figure, further discussions added and relevant references
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Looking into the matter of light-quark hadrons
In tackling QCD, a constructive feedback between theory and extant and
forthcoming experiments is necessary in order to place constraints on the
infrared behaviour of QCD's \beta-function, a key nonperturbative quantity in
hadron physics. The Dyson-Schwinger equations provide a tool with which to work
toward this goal. They connect confinement with dynamical chiral symmetry
breaking, both with the observable properties of hadrons, and hence provide a
means of elucidating the material content of real-world QCD. This contribution
illustrates these points via comments on: in-hadron condensates; dressed-quark
anomalous chromo- and electro-magnetic moments; the spectra of mesons and
baryons, and the critical role played by hadron-hadron interactions in
producing these spectra.Comment: 11 pages, 7 figures. Contribution to the Proceedings of "Applications
of light-cone coordinates to highly relativistic systems - LIGHTCONE 2011,"
23-27 May, 2011, Dallas. The Proceedings will be published in Few Body
System
Collective perspective on advances in Dyson-Schwinger Equation QCD
We survey contemporary studies of hadrons and strongly interacting quarks
using QCD's Dyson-Schwinger equations, addressing: aspects of confinement and
dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and
transition form factors, from small- to large-Q^2; parton distribution
functions; the physics of hadrons containing one or more heavy quarks; and
properties of the quark gluon plasma.Comment: 56 pages. Summary of lectures delivered by the authors at the
"Workshop on AdS/CFT and Novel Approaches to Hadron and Heavy Ion Physics,"
2010-10-11 to 2010-12-03, hosted by the Kavli Institute for Theoretical
Physics, China, at the Chinese Academy of Science