42 research outputs found
The quark-photon vertex and meson electromagnetic form factors
The ladder Bethe-Salpeter solution for the dressed photon-quark vertex is
used to study the low-momentum behavior of the pion electromagnetic and the
transition form factors. With model parameters
previously fixed by light meson masses and decay constants, the low-momentum
slope of both form factors is in excellent agreement with the data. In
comparison, the often-used Ball-Chiu Ansatz for the vertex is found to be
deficient; less than half of the obtained is generated by that Ansatz
while the remainder of the charge radius could be attributed to the tail of the
resonance.Comment: 4 pages, 2 figures, uses espcrc1.sty, talk presented at PANIC99,
Uppsala, Swede
The Quark-Photon Vertex and the Pion Charge Radius
The rainbow truncation of the quark Dyson-Schwinger equation is combined with
the ladder Bethe-Salpeter equation for the dressed quark-photon vertex to study
the low-momentum behavior of the pion electromagnetic form factor. With model
gluon parameters previously fixed by the pion mass and decay constant, the pion
charge radius is found to be in excellent agreement with the data. When
the often-used Ball-Chiu Ansatz is used to construct the quark-photon vertex
directly from the quark propagator, less than half of is generated.
The remainder of is seen to be attributable to the presence of the
-pole in the solution of the ladder Bethe-Salpeter equation.Comment: 21 pages, 9 figure
Selected nucleon form factors and a composite scalar diquark
A covariant, composite scalar diquark, Fadde'ev amplitude model for the
nucleon is used to calculate pseudoscalar, isoscalar- and isovector-vector,
axial-vector and scalar nucleon form factors. The last yields the nucleon
sigma-term and on-shell sigma-nucleon coupling. The calculated form factors are
soft, and the couplings are generally in good agreement with experiment and
other determinations. Elements in the dressed-quark-axial-vector vertex that
are not constrained by the Ward-Takahashi identity contribute ~20% to the
magnitude of g_A. The calculation of the nucleon sigma-term elucidates the only
unambiguous means of extrapolating meson-nucleon couplings off the meson
mass-shell.Comment: 12 pages, REVTEX, 5 figures, epsfi
Nonperturbative QCD Phenomenology and Light Quark Physics
Recent progress in modeling QCD for hadron physics through truncated
Dyson-Schwinger equations is reviewed. Special emphasis is put upon comparison
of dressed quark propagators and the dressed quark-gluon vertex with
lattice-QCD results.Comment: 6 pages, 7 figures. Invited talk at the QCD Down Under workshop at
the CSSM/University of Adelaide, March 200
Covariant QCD Modeling of Light Meson Physics
We summarize recent progress in soft QCD modeling based on the set of
Dyson--Schwinger equations truncated to ladder-rainbow level. This covariant
approach to hadron physics accommodates quark confinement and implements the
QCD one-loop renormalization group behavior. We compare the dressed quark
propagator, pseudoscalar and vector meson masses as a function of quark mass,
and the rho -> pi pi coupling to recent lattice-QCD data. The error in the
Gell-Mann--Oakes--Renner relation with increasing quark mass is quantified by
comparison to the exact pseudoscalar mass relation as evaluated within the
ladder-rainbow Dyson-Schwinger model.Comment: Presented at the International School on Nuclear Physics, 24th
course: Quarks in Nuclei, Erice, Sicily, September 2002; to be published in
Prog. Part. Nucl. Phys.; 6 pages, 6 fig
High-Spin "Stretched" States Excited in (p,n) Reactions
This work was supported by the National Science Foundation Grant NSF PHY 78-22774 A02 & A03 and by Indiana Universit
High-Spin States in Nuclei Excited Via the (p,n) Reactions
Supported by the National Science Foundation and Indiana Universit
Neutron Knockout Reactions
This work was supported by the National Science Foundation Grant NSF PHY 78-22774 A02 & A03 and by Indiana Universit
Spectroscopy with the (d,n) Reaction at 80 MeV
This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit
Charge symmetry breaking via rho-omega mixing from model quark-gluon dynamics
The quark-loop contribution to the mixing self-energy
function is calculated using a phenomenologically successful QCD-based model
field theory in which the and mesons are composite
bound states. In this calculation the dressed quark propagator, obtained from a
model Dyson-Schwinger equation, is confining. In contrast to previous studies,
the meson- vertex functions are characterised by a strength and range
determined by the dynamics of the model; and the calculated off-mass-shell
behaviour of the mixing amplitude includes the contribution from the calculated
diagonal meson self-energies. The mixing amplitude is shown to be very
sensitive to the small isovector component of dynamical chiral symmetry
breaking. The spacelike quark-loop mixing-amplitude generates an insignificant
charge symmetry breaking nuclear force.Comment: 11 Pages, 3 figures uuencoded and appended to this file, REVTEX 3.0.
ANL-PHY-7718-TH-94, KSUCNR-004-94. [!! PostScript file format corrected.
Retrieve by anonymous ftp from theory.phy.anl.gov (130.202.20.190), directory
pub: mget wpfig*.ps Three files.