New Types of Meson-Exchange Currents in Few-Nucleon Systems Based on Dressed-Bag Model for NN Interaction

Abstract

A new model for basic NN-force has been developed in recent years by Moscow-Tübingen group [1]. The model assumes that two p-shell excited quarks in proper six-quark description for the NN-channel with a microscopic configuration \(\left| s^4p^2[42]_xL =0,2; ST \right \rangle\) deexcites via well known 3P0-mechanism into two s-wave pions and then pass to the two s-shell quarks. This leads to production of the intermediate state in NN-interaction in the form of a dressed six-quark bag: \(\left|s^6[6]_x + \sigma, L_\sigma = 0,2; S_\sigma = T_\sigma = 0\right \rangle\) and \(\left|s^6[6]_x + 2\pi, L_{2\pi} = 0,2; S_{2\pi} = 0, T_{2\pi} = 1\right \rangle\) at intermediate and short-range region. In the transition NN 2192; 6q + σ a strong scalar-isoscalar field φ σ (represented by σ meson production) is generated due to partial restoration of chiral symmetry. This spherical symmetric σ-field around 6q-bag results in strong effective “pressure” to six-quark bag from outside, which leads effectively to a strong attraction in the associated NN-channel. The external pressure to the six-quark core induced by σ-field generation in this approach is confronted with the so-called t-channel σ-exchange in traditional meson-exchange models. Similarly two meson-generation mechanism leads to the appearance of charged currents in the dressed bag (see Fig.1). These charged currents are different from traditional π±-currents in NN-channel due to their s-channel nature [2], but having the similar to the traditional MEC tensor structure of current operators. This non-trivial similarity leads to the same “selection rules” in our approach as in traditional MEC-operators.