53 research outputs found
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
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
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
Theory and Phenomenology of Hadrons
This Dyson-Schwinger equation (DSE) aperc,u highlights recent applications to
mesons. It reports features of, and results for, pseudoscalar and scalar
bound-state residues in vacuum polarisations, and exhibits how a restoration of
chiral symmetry in meson trajectories could be manifest in a relationship
between them. It also touches on nucleon studies, emphasising the importance of
both scalar and axial-vector diquark correlations, and reporting the
calculation of mu_n G_E^n(Q^2)/G_M^n(Q^2). The value of respecting symmetries,
including Poincare' covariance, is stressed.Comment: 7 pages, 1 figure, contribution to proceedings of "18th International
IUPAP Conference on Few-Body Problems in Physics," Santos, Brazil, August
21-26, 200
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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Quark-gluon vertex in general kinematics
The original publication can be found at www.springerlink.com Submitted to Cornell University’s online archive www.arXiv.org in 2007 by Jon-Ivar Skullerud. Post-print sourced from www.arxiv.org.We compute the quark–gluon vertex in quenched lattice QCD in the Landau gauge, using an off-shell mean-field O(a)-improved fermion action. The Dirac-vector part of the vertex is computed for arbitrary kinematics. We find a substantial infrared enhancement of the interaction strength regardless of the kinematics.Ayse Kizilersu, Derek B. Leinweber, Jon-Ivar Skullerud and Anthony G. William
Manifestation of three-body forces in three-body Bethe-Salpeter and light-front equations
Bethe-Salpeter and light-front bound state equations for three scalar
particles interacting by scalar exchange-bosons are solved in ladder
truncation. In contrast to two-body systems, the three-body binding energies
obtained in these two approaches differ significantly from each other: the
ladder kernel in light-front dynamics underbinds by approximately a factor of
two compared to the ladder Bethe-Salpeter equation. By taking into account
three-body forces in the light-front approach, generated by two exchange-bosons
in flight, we find that most of this difference disappears; for small exchange
masses, the obtained binding energies coincide with each other.Comment: 24 pages, 8 figures, submitted in Few-Body System
Analytic properties of the Landau gauge gluon and quark propagators
We explore the analytic structure of the gluon and quark propagators of
Landau gauge QCD from numerical solutions of the coupled system of renormalized
Dyson--Schwinger equations and from fits to lattice data. We find sizable
negative norm contributions in the transverse gluon propagator indicating the
absence of the transverse gluon from the physical spectrum. A simple analytic
structure for the gluon propagator is proposed. For the quark propagator we
find evidence for a mass-like singularity on the real timelike momentum axis,
with a mass of 350 to 500 MeV. Within the employed Green's functions approach
we identify a crucial term in the quark-gluon vertex that leads to a positive
definite Schwinger function for the quark propagator.Comment: 42 pages, 16 figures, revtex; version to be published in Phys Rev
Electromagnetic superconductivity of vacuum induced by strong magnetic field
The quantum vacuum may become an electromagnetic superconductor in the
presence of a strong external magnetic field of the order of 10^{16} Tesla. The
magnetic field of the required strength (and even stronger) is expected to be
generated for a short time in ultraperipheral collisions of heavy ions at the
Large Hadron Collider. The superconducting properties of the new phase appear
as a result of a magnetic-field-assisted condensation of quark-antiquark pairs
with quantum numbers of electrically charged rho mesons. We discuss
similarities and differences between the suggested superconducting state of the
quantum vacuum, a conventional superconductivity and the Schwinger pair
creation. We argue qualitatively and quantitatively why the superconducting
state should be a natural ground state of the vacuum at the sufficiently strong
magnetic field. We demonstrate the existence of the superconducting phase using
both the Nambu-Jona-Lasinio model and an effective bosonic model based on the
vector meson dominance (the rho-meson electrodynamics). We discuss various
properties of the new phase such as absence of the Meissner effect, anisotropy
of superconductivity, spatial inhomogeneity of ground state, emergence of a
neutral superfluid component in the ground state and presence of new
topological vortices in the quark-antiquark condensates.Comment: 37 pages, 14 figures, to appear in Lect. Notes Phys. "Strongly
interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K.
Landsteiner, A. Schmitt, H.-U. Ye
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
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