38 research outputs found
Meson Transition Form Factors From A QCD Model Field Theory
We discuss form factors and coupling constants for the , and interactions generated by a model
field theory that produces finite size meson modes. The approach
implements dressing of the vertices and propagators consistent with dynamical
chiral symmetry breaking, gauge invariance, quark confinement and perturbative
QCD.Comment: 10 pages incl 4 figs in a single gzip-ed, uuencoded Postscript file;
Paper presented at {\it The International School of Nuclear Physics: Quarks
in Hadrons and Nuclei}, Erice, September 1995; Proceedings to appear in Prog.
Part. Nucl. Phys. {\bf 36
Goldstone Theorem and Diquark Confinement Beyond Rainbow-Ladder Approximation
The quark Dyson-Schwinger equation and meson Bethe-Salpeter equation are
studied in a truncation scheme that extends the rainbow-ladder approximation
such that, in the chiral limit, the isovector, pseudoscalar meson remains
massless. Quark-quark (diquark) correlations, which are bound in rainbow-ladder
approximation, are destabilised by repulsive contributions that only appear at
higher order in the Bethe-Salpeter kernel. The net effect of higher order terms
on the meson bound-state masses is small.Comment: 11 pages, LaTeX, elsart.sty, 3 EPS figure
Extended Chiral Transformations Including Diquark Fields as Parameters
We introduce extended chiral transformation, which depends both on
pseudoscalar and diquark fields as parameters and determine its group
structure. Assuming soft symmetry breaking in diquark sector, bosonisation of a
quasi-Goldstone -diquark is performed. In the chiral limit the -diquark
mass is defined by the gluon condensate, . The diquark
charge radius is .Comment: Latex file, to apear in Phis. Lett.
The mixed quark-gluon condensate from an effective quark-quark interaction
We exhibit the method for obtaining non perturbative quark and gluonic vacuum
condensates from a model truncation of QCD. The truncation allows for a
phenomenological description of the quark-quark interaction in a framework
which maintains all global symmetries of QCD and allows an 1/N_c expansion.
Within this approach the functional integration over the gluon fields can be
performed and therefore any gluonic vacuum observable can be expressed in terms
of a quark operator and the gluon propagator. As a special case we calculate
the mixed quark gluon condensate. We investigate how the value depends on the
form of the model quark-quark interaction. A comparison with the results of
quenched lattice QCD, the instanton liquid model and QCD sum rules is drawn.Comment: 10 pages, no figures, LATEX using elsart.sty, minor corrections in
some formulas, some references added, to be published in PL
Meson masses within the model of induced nonlocal quark currents
The model of induced quark currents formulated in our recent paper (Phys.
Rev. D51, 176) is developed. The model being a kind of nonlocal extension of
the bosonization procedure is based on the hypothesis that the QCD vacuum is
realized by the (anti-)self-dual homogeneous gluon field. This vacuum field
provides the analytical quark confinement. It is shown that a particular form
of nonlocality of the quark and gluon propagators determined by the vacuum
field, an interaction of quark spin with the vacuum gluon field and a
localization of meson field at the center of masses of two quarks can explain
the distinctive features of meson spectrum: Regge trajectories of radial and
orbital excitations, mass splitting between pseudoscalar and vector mesons, the
asymptotic mass formulas in the heavy quark limit: for
quarkonia and for heavy-light mesons. With a minimal set
of parameters (quark masses, vacuum field strength and the quark-gluon coupling
constant) the model describes to within ten percent inaccuracy the masses and
weak decay constants of mesons from all qualitatively different regions of the
spectrum.Comment: 31 pages, LaTe
Mixed tensor susceptibility of the QCD vacuum from effective quark-quark interactions
We calculate the mixed tensor susceptibility of QCD vacuum in the framework
of the global color symmetry model. In our calculation, the functional
integration over gluon fields can be performed and the gluonic vacuum
observable can be expressed in terms of the quark operators and the gluon
propagator. The mixed tensor susceptibility was obtained with the subtraction
of the perturbative contribution which is evaluated by the Wigner solution of
the quark gap equation. Using several different effective quark-quark
interaction models, we find the values of the mixed tensor susceptibility are
very small.Comment: 12 page
Nonperturbative aspects of the quark-photon vertex
The electromagnetic interaction with quarks is investigated through a
relativistic, electromagnetic gauge-invariant treatment. Gluon dressing of the
quark-photon vertex and the quark self-energy functions is described by the
inhomogeneous Bethe-Salpeter equation in the ladder approximation and the
Schwinger-Dyson equation in the rainbow approximation respectively. Results for
the calculation of the quark-photon vertex are presented in both the time-like
and space-like regions of photon momentum squared, however emphasis is placed
on the space-like region relevant to electron scattering. The treatment
presented here simultaneously addresses the role of dynamically generated
vector bound states and the approach to asymptotic behavior. The
resulting description is therefore applicable over the entire range of momentum
transfers available in electron scattering experiments. Input parameters are
limited to the model gluon two-point function, which is chosen to reflect
confinement and asymptotic freedom, and are largely constrained by the obtained
bound-state spectrum.Comment: 8 figures available on request by email, 25 pages, Revtex,
DOE/ER/40561-131-INT94-00-5
Quark-Antiquark Bound States within a Dyson-Schwinger Bethe-Salpeter Formalism
Pion and kaon observables are calculated using a Dyson-Schwinger
Bethe-Salpeter formalism. It is shown that an infrared finite gluon propagator
can lead to quark confinement via generation of complex mass poles in quark
propagators. Observables, including electromagnetic form factors, are
calculated entirely in Euclidean metric for spacelike values of bound state
momentum and final results are extrapolated to the physical region.Comment: Minor typographical corrections. Accepted for publication in Nucl.
Phys.
Dyson-Schwinger Equations and the Application to Hadronic Physics
We review the current status of nonperturbative studies of gauge field theory
using the Dyson-Schwinger equation formalism and its application to hadronic
physics. We begin with an introduction to the formalism and a discussion of
renormalisation in this approach. We then review the current status of studies
of Abelian gauge theories [e.g., strong coupling quantum electrodynamics]
before turning our attention to the non-Abelian gauge theory of the strong
interaction, quantum chromodynamics. We discuss confinement, dynamical chiral
symmetry breaking and the application and contribution of these techniques to
our understanding of the strong interactions.Comment: 110 pages, LaTeX. Replaced only to facilitate retrieval. Also
available at /u/ftp/pub/Review.uu via anonymnous-ft
Solitons in a chiral quark model with non-local interactions
Hedgehog solitons are found in a chiral quark model with non-local
interactions. The solitons are stable without the chiral-circle constraint for
the meson fields, as was assumed in previous Nambu-Jona--Lasinio model with
local interactions.Comment: 8 page