141 research outputs found
The hadron-quark transition with a lattice of nonlocal confining solitons
We use a lattice of nonlocal confining solitons to describe nuclear matter in
the Wigner-Seitz approximation. The average density is varied by changing the
size of the Wigner-Seitz cell. At sufficiently large density quark energy bands
develop. The intersection of the filled valence band with the next empty band
at a few times standard nuclear density signals a transition from a color
insulator to a color conductor and is identified with the critical density for
quark deconfinement.Comment: 12 pages Latex with one PS figur
The analytic structure of heavy quark propagators
The renormalised quark Dyson-Schwinger equation is studied in the limit of
the renormalised current heavy quark mass m_R --> infinity. We are particularly
interested in the analytic pole structure of the heavy quark propagator in the
complex momentum plane. Approximations in which the quark-gluon vertex is
modelled by either the bare vertex or the Ball-Chiu Ansatz, and the Landau
gauge gluon propagator takes either a gaussian form or a gaussian form with an
ultraviolet asymptotic tail are used.Comment: 21 pages Latex and 5 postscript figures. The original version of this
paper has been considerably extended to include a formalism dealing with the
renormalised heavy quark Dyson-Schwinger equation and uses a more realistic
Ansatz for the gluon propagator
Nucleon form factors and a nonpointlike diquark
Nucleon form factors are calculated on q^2 in [0,3] GeV^2 using an Ansatz for
the nucleon's Fadde'ev amplitude motivated by quark-diquark solutions of the
relativistic Fadde'ev equation. Only the scalar diquark is retained, and it and
the quark are confined. A good description of the data requires a nonpointlike
diquark correlation with an electromagnetic radius of 0.8 r_pi. The composite,
nonpointlike nature of the diquark is crucial. It provides for diquark-breakup
terms that are of greater importance than the diquark photon absorption
contribution.Comment: 5 pages, REVTEX, epsfig, 3 figure
Ground-state Spectrum of Light-quark Mesons
A confining, Goldstone theorem preserving, separable Ansatz for the ladder
kernel of the two-body Bethe-Salpeter equation is constructed from
phenomenologically efficacious , and dressed-quark propagators. The
simplicity of the approach is its merit. It provides a good description of the
ground-state isovector-pseudoscalar, vector and axial-vector meson spectrum;
facilitates an exploration of the relative importance of various components of
the two-body Bethe-Salpeter amplitudes, showing that sub-leading Dirac
components are quantitatively important in the isovector-pseudoscalar meson
channels; and allows a scrutiny of the domain of applicability of ladder
truncation studies. A colour-antitriplet diquark spectrum is obtained.
Shortcomings of separable Ans\"atze and the ladder kernel are highlighted.Comment: 30 pages, LaTeX/REVTEX 3.0, no figure
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
The Calculation of Vacuum Properties from the Global Color Symmetry Model
A modified method for calculating the non-perturbative quark vacuum
condensates from the global color symmetry model is derived. Within this
approach it is shown that the vacuum condensates are free of ultraviolet
divergence which is different from previous studies. As a special, the
two-quark condensate and the mixed quark-gluon condensate are calculated. A
comparision with the results of the other nonperturbative QCD approaches is
given.Comment: 17 page
Mesons as qbar-q Bound States from Euclidean 2-Point Correlators in the Bethe-Salpeter Approach
We investigate the 2-point correlation function for the vector current. The
gluons provide dressings for both the quark self energy as well as the vector
vertex function, which are described consistently by the rainbow
Dyson-Schwinger equation and the inhomogeneous ladder Bethe-Salpeter equation.
The form of the gluon propagator at low momenta is modeled by a 2-parameter
ansatz fitting the weak pion decay constant. The quarks are confined in the
sense that the quark propagator does not have a pole at timelike momenta. We
determine the ground state mass in the vector channel from the Euclidean time
Fourier transform of the correlator, which has an exponential falloff at large
times. The ground state mass lies around 590 MeV and is almost independent of
the model form for the gluon propagator. This method allows us to stay in
Euclidean space and to avoid analytic continuation of the quark or gluon
propagators into the timelike region.Comment: 21 pages (REVTEX), 8 Postscript figure
Approximation of the Schwinger--Dyson and the Bethe--Salpeter Equations and Chiral Symmetry of QCD
The Bethe--Salpeter equation for the pion in chiral symmetric models is
studied with a special care to consistency with low-energy relations. We
propose a reduction of the rainbow Schwinger--Dyson and the ladder
Bethe--Salpeter equations with a dressed gluon propagator. We prove that the
reduction preserves the Ward--Takahashi identity for the axial-vector current
and the PCAC relation.Comment: 10 pages, LaTe
A Non-perturbative Treatment of Heavy Quarks and Mesons
A formalism for studying heavy quarks in terms of model Dyson-Schwinger
equations is developed. The formalism is the natural extension of a technique
which has proved successful in a number of studies of light hadron physics. The
dressed heavy quark propagator, calculated to leading order in the inverse
quark mass, is incorporated in a treatment of mesons consisting of a heavy
quark and light antiquark via the ladder approximation Bethe-Salpeter equation.
In the limit of infinite heavy quark mass the model is found to respect the
spectrum degeneracies present in Heavy Quark Effective Theory. An exploratory
numerical analysis of a simple form of the model is carried out to assess its
viability for studying and mesons.Comment: 20 pages, 3 postscript figures, alterations mainly rewriting of
Section VI (Numerical calculations
Off Mass Shell Effects in Hadron Electric Dipole Moments
We note that off the quark mass shell the operators
and , both of which reduce to
in the non-relativistic limit, are no longer
identical. In this paper we explore the effects of this difference in the
contribution of these quark electric moments to hadronic electric moments.Comment: 21 pages, 1 figure, Revtex, uses psfi
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