S. A. Coon

Repulsive short range three-nucleon interaction

The three-nucleon interaction that is implied by the pion and the effective scalar and vector meson exchange components of the nucleon-nucleon interaction arises from the excitation of intermediate nucleon-antinucleon pairs. Using several wave-function models we show that this interaction is repulsive, reducing the calculated binding energy of the trinucleons by about 200\char21{}300 keV. The contributions of intermediate N(1440) resonances (and the same meson exchanges) to this three-nucleon interaction are also estimated and shown to be small.

Λ -neutron scattering lengths from radiative K − capture

Radiative capture of the K − by the deuteron is examined as a reaction for measurement of the �-neutron scattering lengths. Using the final state interaction, analogous to measurements of the radiative capture of pions by deuterium, the scattering lengths of both the triplet and singlet �-n interaction can be inferred. The problem of the separation of these two fundamental parameters without and with spin information in the experiment is addressed. It is shown that a measurement of the deviation of the vector deuteron polarization asymmetry from –1 provides a direct determination of the difference of the singlet and triplet scattering lengths.

Neutron charge radius and the Dirac equation

We consider the Dirac equation for a finite-size neutron in an external electric field. We explicitly incorporate Dirac-Pauli form factors into the Dirac equation. After a non-relativistic reduction, the Darwin-Foldy term is cancelled by a contribution from the Dirac form factor, so that the only coefficient of the external field charge density is

Vector meson dominance and {rho}-{omega} mixing

e/6 r^2_{En}

Relativistic corrections to the electric polarizability of the neutron

, i. e. the root mean square radius associated with the electric Sachs form factor . Our result is similar to a recent result of Isgur, and reconciles two apparently conflicting viewpoints about the use of the Dirac equation for the description of nucleons.

Chiral Symmetry and Low Energy Pion-Nucleon Scattering

The scale of a phenomenologically successful charge-symmetry-violating nucleon-nucleon interaction, that attributed to meson exchange with a {Delta}I=1 {rho}-{omega} transition, is set by the Coleman-Glashow SU(2)-breaking tadpole mechanism. A single tadpole scale has been obtained from symmetry arguments, electromagnetic meson and baryon measured mass splittings, and the observed isospin-violating ({Delta}I=1) decay {omega}{r_arrow}{pi}{sup +}{pi}{sup {minus}}. The hadronic realization of this tadpole mechanism lies in the I=1 a{sub 0} scalar meson. We show that measured hadronic and two-photon widths of the a{sub 0} meson, with the aid of the vector meson dominance model, recover the universal Coleman-Glashow tadpole scale. {copyright} {ital 1998} {ital The American Physical Society}

Off-mass-shell πN scattering and pp→ppπ0

We demonstrate in a solvable model the connection between the intrinsic electric polarizability ᾱ and the value α Sch obtained from neutron- atom scattering.

{lambda}-neutron scattering lengths from radiative K{sup -} capture

In these lectures, I examine the effect of the meson factory πN data on the current algebra/PCAC program which describes chiral symmetry breaking in this system. After historical remarks on the current algebra/PCAC versus chiral Lagrangians approaches to chiral symmetry, and description of the need for πN amplitudes with virtual (off-mass-shell) pions in nuclear force models and other nuclear physics problems, I begin with kinematics and isospin aspects of the invariant amplitudes. A detailed introduction to the hadronic vector and axial-vector currents and the hypothesis of partially conserved axial-vector currents (PCAC) follows. I review and test against contemporary data the PCAC predictions of the Goldberger-Treiman relation, and the Adler consistency condition for a πN amplitude. Then comes a detailed description of the current algebra Ward-Takahashi identities in the chiral limit and a brief account of the on-shell current algebra Ward-Takahashi identities. The latter identities form the basis of so-called current algebra models of πN scattering. I then test these models against the contemporary empirical πN amplitudes extrapolated into the subthreshold region via dispersion relations. The scale and the t dependence of the “sigma term” is determined by the recent data.

Lambda neutron scattering lengths from radiative K- capture

We adapt the off-shell πN amplitude of the Tucson-Melbourne three-body force to the half-off-shell amplitude of the pion rescattering contribution to pp→ppπ0 near threshold. This pion rescattering contribution, together with the impulse term, provides a good description of the data when the half-off-shell amplitude is linked to the phenomenological invariant amplitudes obtained from meson factory πN scattering data.

Λ-neutron scattering lengths from radiativeK−capture

Radiative capture of the K − by the deuteron is examined as a reaction for measurement of the �-neutron scattering lengths. Using the final state interaction, analogous to measurements of the radiative capture of pions by deuterium, the scattering lengths of both the triplet and singlet �-n interaction can be inferred. The problem of the separation of these two fundamental parameters without and with spin information in the experiment is addressed. It is shown that a measurement of the deviation of the vector deuteron polarization asymmetry from –1 provides a direct determination of the difference of the singlet and triplet scattering lengths.