Meson exchange potentials in an NN quark model with quark-antiquark excitations

Abstract

In a recent quark-model study of the NN interaction, we explicitly incorporated the qq excitations inherent in the quark-gluon interaction lagrangian into the model space, and examined the contributions to the NN potential of particular components of the single-nucleon wave function, with specific baryon and meson quantum numbers, through the Wigner transforms of the resultant coupling terms of the quark exchange kernels. The present investigation focuses on the long-range parts of the potentials. It is shown that these arise almost entirely through two of the 25 possible types of exchange terms, and that these two correspond to the simple exchange of a pair between the two nucleons and contribute only through coupling terms for which the (3q) components have the quantum numbers of a nucleon and the component the color-singlet character of a real pseudoscalar or vector meson. The potentials arising from these simple color-singlet exchanges have been evaluated in explicit analytic form. In their dependence on nucleon ([sigma]1, [middle dot] [sigma]2) and ([tau]1 [middle dot] [tau]2) factors and the relative importance and signs of spin-spin, spin-independent central, LS, and tensor terms they have all the characteristics of conventional OBEP's. They are in remarkably good agreement with conventional OBEP's in the r [ges] 1.2 fm range and have the same qualitative radial features over an even wider range, the one exception being the steep short-range repulsive rise of the spin-independent central term of the [omega]-exchange potential. The corresponding exchange potential instead changes sign to become attractive at r < 0.8 fm.