Meson PVV Interactions are determined by Quark Loops

We show that all abnormal parity three-body meson interactions can be adequately described by quark loops, evaluated at zero external momentum, with couplings determined by $U(N_f)$ symmetry. We focus primarily on radiative meson decays which involve one pseudoscalar. The agreement with experiment for non-rare decays is surprisingly good and requires very few parameters, namely the coupling constants $g_{\pi qq}$ and $g_{\rho qq}$ and some mixing angles. This agreement extends to some three-body decays that are dominated by pion pairs in a P-wave state.Comment: 21 pages, Revtex, one figur

Analysis of three-nucleon forces effects in the A=3A=3 system

Using modern nucleon-nucleon interactions in the description of the $A=3,4$ nuclear systems the $\chi^2$ per datum results to be much bigger than one. In particular it is not possible to reproduce the three- and four-nucleon binding energies and the $n-d$ scattering length simultaneously. This is one manifestation of the necessity of including a three-nucleon force in the nuclear Hamiltonian. In this paper we perform an analysis of some, widely used, three-nucleon force models. We analyze their capability to describe the aforementioned quantities and, to improve their description, we propose modifications in the parametrization of the models. The effects of these new parametrization are studied in some polarization observables at low energies.Comment: 10 pages, to be published in Few-Body Systems. Presented at the workshop on "Relativistic Description of Two- and Three-body Systems in Nuclear Physics" ECT* Trento, 19 - 23 October 200

Momentum and Coordinate Space Three-nucleon Potentials

In this paper we give explicit formulae in momentum and coordinate space for the three-nucleon potentials due to $\rho$ and $\pi$ meson exchange, derived from off-mass-shell meson-nucleon scattering amplitudes which are constrained by the symmetries of QCD and by the experimental data. Those potentials have already been applied to nuclear matter calculations. Here we display additional terms which appear to be the most important for nuclear structure. The potentials are decomposed in a way that separates the contributions of different physical mechanisms involved in the meson-nucleon amplitudes. The same type of decomposition is presented for the $\pi - \pi$ TM force: the $\Delta$, the chiral symmetry breaking and the nucleon pair terms are isolated.Comment: LATEX, 33 pages, 3 figures (available as postscript files upon request

Can neutron electromagnetic form factors be obtained by polarized inclusive electron scattering off polarized three-nucleon bound states?

The investigation of the electromagnetic inclusive responses of polarized $^{3}$He within the plane wave impulse approximation is briefly reported. A particular emphasys is put on the extraction, from the inclusive responses at the quasielastic peak, of the neutron form factors from feasible experiments.Comment: 6 pages, Latex, 4 Postscript figures. Presented to XVth Conference on "Few-body problems in Physics", Groningen July 1997.To appear in Nucl. Phys.

ρ\rho-ω\omega mixing and spin dependent CSV potential

We construct the charge symmetry violating (CSV) nucleon-nucleon potential induced by the $\rho^0$-\o mixing due to the neutron-proton mass difference driven by the $NN$ loop. Analytical expression for for the two-body CSV potential is presented containing both the central and non- central $NN$ interaction. We show that the $\rho$$NN$ tensor interaction can significantly enhance the charge symmetry violating $NN$ interaction even if momentum dependent off-shell $\rho^0$-$\omega$ mixing amplitude is considered. It is also shown that the inclusion of form factors removes the divergence arising out of the contact interaction. Consequently, we see that the precise size of the computed scattering length difference depends on how the short range aspects of the CSV potential are treated.Comment: Accepted for publication in Phys. Rev.

Quadratic momentum dependence in the nucleon-nucleon interaction

We investigate different choices for the quadratic momentum dependence required in nucleon-nucleon potentials to fit phase shifts in high partial-waves. In the Argonne v18 potential L**2 and (L.S)**2 operators are used to represent this dependence. The v18 potential is simple to use in many-body calculations since it has no quadratic momentum-dependent terms in S-waves. However, p**2 rather than L**2 dependence occurs naturally in meson-exchange models of nuclear forces. We construct an alternate version of the Argonne potential, designated Argonne v18pq, in which the L**2 and (L.S)**2 operators are replaced by p**2 and Qij operators, respectively. The quadratic momentum-dependent terms are smaller in the v18pq than in the v18 interaction. Results for the ground state binding energies of 3H, 3He, and 4He, obtained with the variational Monte Carlo method, are presented for both the models with and without three-nucleon interactions. We find that the nuclear wave functions obtained with the v18pq are slightly larger than those with v18 at interparticle distances < 1 fm. The two models provide essentially the same binding in the light nuclei, although the v18pq gains less attraction when a fixed three-nucleon potential is added.Comment: v.2 important corrections in tables and minor revisions in text; reference for web-posted subroutine adde

Local three-nucleon interaction from chiral effective field theory

The three-nucleon (NNN) interaction derived within the chiral effective field theory at the next-to-next-to-leading order (N2LO) is regulated with a function depending on the magnitude of the momentum transfer. The regulated NNN interaction is then local in the coordinate space, which is advantages for some many-body techniques. Matrix elements of the local chiral NNN interaction are evaluated in a three-nucleon basis. Using the ab initio no-core shell model (NCSM) the NNN matrix elements are employed in 3H and 4He bound-state calculations.Comment: 17 pages, 9 figure

A New Treatment of 2N and 3N Bound States in Three Dimensions

The direct treatment of the Faddeev equation for the three-boson system in 3 dimensions is generalized to nucleons. The one Faddeev equation for identical bosons is replaced by a strictly finite set of coupled equations for scalar functions which depend only on 3 variables. The spin-momentum dependence occurring as scalar products in 2N and 3N forces accompanied by scalar functions is supplemented by a corresponding expansion of the Faddeev amplitudes. After removing the spin degrees of freedom by suitable operations only scalar expressions depending on momenta remain. The corresponding steps are performed for the deuteron leading to two coupled equations.Comment: 19 page

Charge-Symmetry-Breaking Three-Nucleon Forces

Leading-order three-nucleon forces that violate isospin symmetry are calculated in Chiral Perturbation Theory. The effect of the charge-symmetry-breaking three-nucleon force is investigated in the trinucleon systems using Faddeev calculations. We find that the contribution of this force to the 3He - 3H binding-energy difference is approximately 5 keV.Comment: 14 pages, 3 figure

Charge-Asymmetry of the Nucleon-Nucleon Interaction

Based upon the Bonn meson-exchange model for the nucleon-nucleon ($NN$) interaction, we study systematically the charge-symmetry-breaking (CSB) of the $NN$ interaction due to nucleon mass splitting. Particular attention is payed to CSB generated by the $2\pi$-exchange contribution to the $NN$ interaction, $\pi\rho$ diagrams, and other multi-meson-exchanges. We calculate the CSB differences in the $^1S_0$ effective range parameters as well as phase shift differences in $S$, $P$ and higher partial waves up to 300 MeV lab. energy. We find a total CSB difference in the singlet scattering length of 1.6 fm which explains the empirical value accurately. The corresponding CSB phase-shift differences are appreciable at low energy in the $^1S_0$ state. In the other partial waves, the CSB splitting of the phase shifts is small and increases with energy, with typical values in the order of 0.1 deg at 300 MeV in $P$ and $D$ waves.Comment: 11 pages, RevTex, 14 figure