126 research outputs found
Baryon Wave Functions in Covariant Relativistic Quark Models
We derive covariant baryon wave functions for arbitrary Lorentz boosts.
Modeling baryons as quark-diquark systems, we reduce their manifestly covariant
Bethe-Salpeter equation to a covariant 3-dimensional form by projecting on the
relative quark-diquark energy. Guided by a phenomenological multigluon exchange
representation of a covariant confining kernel, we derive for practical
applications explicit solutions for harmonic confinement and for the MIT Bag
Model. We briefly comment on the interplay of boosts and center-of-mass
corrections in relativistic quark models.Comment: 13 pages, 4 figure
Relativistic Covariance and Quark-Diquark Wave Functions
We derive covariant wave functions for hadrons composed of two constituents
for arbitrary Lorentz boosts. Focussing explicitly on baryons as quark-diquark
systems, we reduce their manifestly covariant Bethe-Salpeter equation to
covariant 3-dimensional forms by projecting on the relative quark-diquark
energy. Guided by a phenomenological multi gluon exchange representation of
covariant confining kernels, we derive explicit solutions for harmonic
confinement and for the MIT Bag Model. We briefly sketch implications of
breaking the spherical symmetry of the ground state and the transition from the
instant form to the light cone via the infinite momentum frame.Comment: 14 pages, 3 figure
Comment on "Forward K+ production in subthreshold pA collisions at 1.0 GeV"
A Comment on the letter by V. Koptev, et al. - Phys. Rev. Lett. 87 (2001)
022301.Comment: 3 Pages, 1 figure (epsfig
Systematics of the Exclusive Meson Production in the Proton-Proton System in Relativistic Quark-Models
We investigate the exclusive production of the pseudoscalar mesons pi0, eta,
eta', K+ and of the vector mesons omega, phi in a microscopic gluon-exchange or
instanton model. We describe the baryons as covariant quark - scalar diquark
systems with harmonic confinement, thus taking into account center-of-mass
corrections and Lorentz contraction in different frames. The excitation of
intermediate baryon resonances is accounted by colorless 2-gluon (soft Pomeron)
exchange. We find that our model accounts for the systematics of the high
precision data on exclusive meson production from various modern proton
factories.Comment: 13 pages, 11 figure
Mesonic Content of the Nucleon and the Roper Resonance
We investigate colorless (mesonic)
3q-q qbar components in the nucleon and the Roper resonance N*(1440).
Starting from constituent quarks and gluons we estimate the excitation of
quark-antiquark pairs in a gluon exchange model with the strong coupling
constant extracted from a comparison with a non-perturbative resonating group
calculation of the pi, eta, rho and omega content of the nucleon. Applying the
same model to the Roper resonance, we find as the most striking result a very
strong scalar-isoscalar sigma content of the N*(1440) with a strength of the
3q-q qbar configurations comparable to the 3q component itself.Comment: 9 pages, 3 figures, 1 table; modified text, new figure
Protoninduced Pion-, Eta- and Kaon-Production at Threshold
We present some details of our recent theoretical investigations on the total
cross section of the reactions , and at threshold. Applying standard nonrelativistic perturbation
theory within the framework of meson exchange models (MEC) to all of the
investigated processes we observe that theory is still far--off from a
quantitative understanding of the existing data, although the qualitative
behaviour of the threshold cross sections can be reproduced. The often quoted
--dependence of the cross section at threshold is due
to a calculational mistake of Koltun and Reitan (1966) and not based on
theoretical grounds, where threebody phasespace behaviour would yield ,
which can be affected by final state and short range effects. To respect the
high momentum transfers for and
relativistic models were developed. Hereby the --production still is
based on MEC, while the production was investigated in the
quark-gluon-picture based on the Bethe--Salpeter formalism.Comment: 4 pages; contribution to BARYONS98, Bonn, Germany, September 199
Multinucleon Mechanisms in Inclusive Subthreshold K+ Production in p+C12 Collisions at 1 GeV
We analyze recent inclusive data on K+ production in proton induced
Lambda-multi nucleon knock out on Carbon 12. We describe collective effects
among the incoming p and bound nucleons in a pi, rho rescattering model via the
excitation of various baryon resonances. We find the dominance of Lambda N and
Lambda NN final states for K+ momenta below 200 MeV/c, while for momenta above
400 MeV/c the data reflect a continuum with an unbound Lambda together with the
bound residual nucleus C 12.Comment: 5 pages, 1 figur
Spin-3/2 fields in the heavy-baryon effective theory
In the framework of the path integral approach we develop the velocity
component formalism for spin-1/2 and -3/2 baryons coupled with pseudoscalar
mesons in the limit of heavy baryons.
Starting from the most general chiral meson-baryon lagrangian including the
invariance of spin-3/2 fields under point transformation we detail various
problems in integrating out the heavy velocity components in the baryon fields
and derive the effective lagrangian for the light components up to
O(1/M_{baryon}).Comment: LaTeX, 9 pages, no figure
Chiral Symmetry in algebraic and analytic approaches
We compare among themselves two different methods for the derivation of
results following from the requirement of polynomial boundedness of tree-level
chiral amplitudes. It is shown that the results of the algebraic approach are
valid also in the framework of the analytical one. This means that the system
of Sum Rules and Bootstrap equations previously obtained with the help of the
latter approach can be analyzed in terms of reducible representations of the
unbroken Chiral group with the known structure of the mass matrix.Comment: LaTeX file, 4 page
Production and Width of the Pentaquark Theta+(1540) in Strangeness Production in the Proton-Proton System
We analyze recent experimental information on the excitation of the
Theta+(1540) pentaquark in the hadronic reaction pp -> p Sigma+ K0. Upon
describing the conventional production process - which serves as a
normalization - in a meson exchange model, we estimate the resonant Theta+
induced cross section and the width of the pentaquark via K - exchange in a
meson-baryon and a quark-gluon model. From a comparison with experiment we
extract information on the width of the Theta+, the p Theta+ K0 coupling
constant in the meson exchange and the relative s or p wave function for a
nucleon-kaon cluster in the Theta+.Comment: 23 pages, 5 figure
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