189 research outputs found
Octet and Decuplet Baryons in a Confining and Covariant Diquark-Quark Model
We treat baryons as bound states of scalar or axialvector diquarks and a
constituent quark which interact through quark exchange. We obtain fully
four-dimensional wave functions for both octet and decuplet baryons as
solutions of the corresponding Bethe-Salpeter equation. Applications currently
under investigation are: electromagnetic and strong form factors and
strangeness production processes.Comment: 4 pages, 1 figure; talk given by R. Alkofer at PANIC 9
Baryon form factors in a diquark-quark bound state description
Nucleon form factors are calculated in a relativistic diquark--quark picture
based on the Nambu--Jona-Lasinio model. The nucleon wave function is obtained
in a static approximation to the quark exchange interaction between the valence
quark and the diquark. We evaluate the valence quark and --diquark
contribution to the nucleon electromagnetic and weak currents. We find
reasonable electric charge radii, magnetic moments as in the additive diquark
model, and . We discuss the dependence on the model parameters.Comment: 10 pages, latex, 1 postscript figure included (uuencoded
Recommended from our members
Molybdenum Disulfide Catalytic Coatings via Atomic Layer Deposition for Solar Hydrogen Production from Copper Gallium Diselenide Photocathodes
We demonstrate that applying atomic layer deposition-derived molybdenum disulfide (MoS2) catalytic coatings on copper gallium diselenide (CGSe) thin film absorbers can lead to efficient wide band gap photocathodes for photoelectrochemical hydrogen production. We have prepared a device that is free of precious metals, employing a CGSe absorber and a cadmium sulfide (CdS) buffer layer, a titanium dioxide (TiO2) interfacial layer, and a MoS2 catalytic layer. The resulting MoS2/TiO2/CdS/CGSe photocathode exhibits a photocurrent onset of +0.53 V vs RHE and a saturation photocurrent density of -10 mA cm-2, with stable operation for >5 h in acidic electrolyte. Spectroscopic investigations of this device architecture indicate that overlayer degradation occurs inhomogeneously, ultimately exposing the underlying CGSe absorber
Nucleons or diquarks? Competition between clustering and color superconductivity in quark matter
We study the instabilities of quark matter in the framework of a generalized
Nambu--Jona-Lasinio model, in order to explore possible competition between
three-quark clustering to form nucleons and diquark formation leading to color
superconductivity. Nucleon and solutions are obtained for the
relativistic Faddeev equation at finite density and their binding energies are
compared with those for the scalar and axial-vector diquarks found from the
Bethe-Salpeter equation. In a model with interactions in both scalar and axial
diquark channels, bound nucleons exist up to nuclear matter density. However,
except at densities below about a quarter of that of nuclear matter, we find
that scalar diquark formation is energetically favored. This raises the
question of whether a realistic phase diagram of baryonic matter can be
obtained from any model which does not incorporate color confinement.Comment: 23 pages (RevTeX), 5 figures (epsf
Production Processes as a Tool to Study Parameterizations of Quark Confinement
We introduce diquarks as separable correlations in the two-quark Green's
function to facilitate the description of baryons as relativistic three-quark
bound states. These states then emerge as solutions of Bethe-Salpeter equations
for quarks and diquarks that interact via quark exchange. When solving these
equations we consider various dressing functions for the free quark and diquark
propagators that prohibit the existence of corresponding asymptotic states and
thus effectively parameterize confinement. We study the implications of
qualitatively different dressing functions on the model predictions for the
masses of the octet baryons as well as the electromagnetic and strong form
factors of the nucleon. For different dressing functions we in particular
compare the predictions for kaon photoproduction, , and
associated strangeness production, with experimental data.
This leads to conclusions on the permissibility of different dressing
functions.Comment: 43 pages, Latex, 28 eps files included via epsfig; version to be
published in Physical Review
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
Baryons in O(4) and Vibron Model
The structure of the reported excitation spectra of the light unflavored
baryons is described in terms of multi-spin valued Lorentz group
representations of the so called Rarita-Schwinger (RS) type (K/2, K/2)* [(1/
2,0)+ (0,1/2)] with K=1,3, and 5. We first motivate legitimacy of such pattern
as fundamental fields as they emerge in the decomposition of triple fermion
constructs into Lorentz representations. We then study the baryon realization
of RS fields as composite systems by means of the quark version of the U(4)
symmetric diatomic rovibron model. In using the U(4)/ O(4)/ O(3)/ O(2)
reduction chain, we are able to reproduce quantum numbers and mass splittings
of the above resonance assemblies. We present the essentials of the four
dimensional angular momentum algebra and construct electromagnetic tensor
operators. The predictive power of the model is illustrated by ratios of
reduced probabilities concerning electric de-excitations of various resonances
to the nucleon.Comment: Phys. Rev. D (in press, 2001
Mesons in a Poincare Covariant Bethe-Salpeter Approach
We develop a covariant approach to describe the low-lying scalar,
pseudoscalar, vector and axialvector mesons as quark-antiquark bound states.
This approach is based on an effective interaction modeling of the
non--perturbative structure of the gluon propagator that enters the quark
Schwinger-Dyson and meson Bethe-Salpeter equations. We consistently treat these
integral equations by precisely implementing the quark propagator functions
that solve the Schwinger-Dyson equations into the Bethe-Salpeter equations in
the relevant kinematical region. We extract the meson masses and compute the
pion and kaon decay constants. We obtain a quantitatively correct description
for pions, kaons and vector mesons while the calculated spectra of scalar and
axialvector mesons suggest that their structure is more complex than being
quark-antiquark bound states.Comment: 18 pages LaTeX, 5 figures; some changes in the presentation, new
results on axial vector mesons in enlarged mixing scheme; version to be
published in Physical Review
Diquarks: condensation without bound states
We employ a bispinor gap equation to study superfluidity at nonzero chemical
potential: mu .neq. 0, in two- and three-colour QCD. The two-colour theory,
QC2D, is an excellent exemplar: the order of truncation of the quark-quark
scattering kernel: K, has no qualitative impact, which allows a straightforward
elucidation of the effects of mu when the coupling is strong. In rainbow-ladder
truncation, diquark bound states appear in the spectrum of the three-colour
theory, a defect that is eliminated by an improvement of K. The corrected gap
equation describes a superfluid phase that is semi-quantitatively similar to
that obtained using the rainbow truncation. A model study suggests that the
width of the superfluid gap and the transition point in QC2D provide reliable
quantitative estimates of those quantities in QCD.Comment: 7 pages, 3 figures, REVTEX, epsfi
- âŠ