arXiv subjects

M. F. Gari

Publications and source records attributed to M. F. Gari.

5 recordsLinked to original sources

arXiv2000

Form Factors of the Nucleon in a Selfconsistent Chiral Model

In the present paper we extend the Schwinger model of the nucleon to the inclusion of loop corrections. Starting from a chiral model of nucleon and delta for the mesons $π,ρ$ and $A_1$ we extend our nonperturbative sefconsistent regularisation scheme to the calculation of the nucleon form factors. Chiral symmetry requires loops according to the interactions ${\cal L}_{ππρ}, {\cal L}_{ρρρ}, {\cal L}_{ρπA_1}, {\cal L}_{ρA_1 A_1}$.The coupling constants are strictly introduced by chiral symmetry. The use of low energy theorems and SU(3) relations allow an otherwise parameterfree calculation of the form factors of the nucleon.

hep-ph↗

arXiv1996

A Consistent Meson-Field-Theoretical Description of PP-Bremsstrahlung

A parameter-free and relativistic extension of the RuhrPot meson-baryon model is used to define the dominant isoscalar meson-exchange currents. We compute pp-bremsstrahlung observables below the $π-$production threshold using a relativistic hadronic current density that includes impulse, wave function re-orthonormalization, meson-recoil, $\bar{\rm N}$N creation and annihilation, $ρπγ$ + $ωπγ$ + $ρηγ$ + $ωηγ$ vector-meson decay and N$Δγ(π,ρ)$ exchange currents. We obtain a good description of the available data. The N$Δγ(π)$ current is shown to dominate the large two-body contributions and closed-form expressions for various non-relativistic approximations are analyzed. An experimental sensitivity to the admixture of pseudo-scalar and pseudo-vector admixture of the NN$π$ interaction is demonstrated. We examine the Lorentz invariance of the NN$\rightleftharpoons$NN $t$-matrices and show a dominantly pseudo-vector NN$π$ coupling renders impulse approximation calculations without boost operators to be essentially exact. Conversely, a similar analysis of the $Δ{\rm N}\rightleftharpoons$NN transitions shows that boost operators and the two-body $NΔγ$ wave function re-orthonormalization meson-recoil currents are required in NN, $Δ$N and $ΔΔ$ coupled channel $t$-matrix applications. The need for additional data is stressed.

nucl-th↗

arXiv1996

Does The 3N-Force Have A Hard Core?

The meson-nucleon dynamics that generates the hard core of the RuhrPot two-nucleon interaction is shown to vanish in the irreducible 3N force. This result indicates a small 3N force dominated by conventional light meson-exchange dynamics and holds for an arbitrary meson-theoretic Lagrangian. The resulting RuhrPot 3N force is defined in the appendix. A completely different result is expected when the Tamm-Dancoff/Bloch-Horowitz procedure is used to define the NN and 3N potentials. In that approach, (e.g. full Bonn potential) both the NN {\it and} 3N potentials contain non-vanishing contributions from the coherent sum of meson-recoil dynamics and the possibility of a large hard core requiring explicit calculation cannot be ruled out.

nucl-th↗

arXiv1995

Meson-Exchange Currents in pp-Bremsstrahlung

The long-standing discrepancy between pp-bremsstrahlung data and calculations based on the relativistic impulse approximation current is substantially reduced by the inclusion of the PV$γ$ and intermediate-state $Δ$-resonance iso-scalar meson-exchange currents. The success of the standard procedures adopted here shows that pp-bremsstrahlung provides a powerful tool for the further study of $T$=1 isoscalar exchange currents. The need for addition high-precision data is stressed.

nucl-th↗

arXiv1995

Sensitivity of pp-Bremsstrahlung to Meson-Exchange Currents

We present pp-bremsstrahlung cross section calculations at the $π$-production threshold to search for kinematics that best differentiate model-dependent descriptions of the NN $t$-matrix and accentuate the contributions of isoscalar meson-exchange currents. Existing optimization procedures are shown to be completely unreliable due to the neglect of meson-exchange currents and phase space variations. We show that phase-space hides the most important differences in model $t$-matrices, but that improved data will be critical to further investigations of exchange currents.

nucl-th↗