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 $pp\to pp \pi^0$, $pp\to pp \eta$ and $pp\to p\Lambda K^+$ 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 $\eta^2$--dependence of the $pp\to pp \pi^0$ 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 $\eta^4$, which can be affected by final state and short range effects. To respect the high momentum transfers for $pp\to pp \eta$ and $pp\to p\Lambda K^+$ relativistic models were developed. Hereby the $\eta$--production still is based on MEC, while the $K^+$ 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