A two-component model is developed for the intermediate-range NN interaction based on a new mechanism with an intermediate symmetric six-quark bag "dressed" by σ and other fields. To calculate the transition amplitude, the microscopic six-quark shell-model in combination with the 3 P 0 -quark pion production mechanism is used. As a result, an effective energy-dependent NN interaction is constructed. The new quark-meson model for the NN interaction has been demonstrated to result in a new type of NN tensor force at intermediate ranges, which is crucially important for the treatment of tensor mixing at intermediate energies. The suggested model is able to describe NN phase shifts in a broad energy range from low energy up to 1 GeV, and the deuteron structure. The generalization of the model results in new spin-orbit 2N and 3N forces and new mesonexchange currents induced by intermediate dressed bag components, and also in the enhancement of a collective σ-field in nuclei. Keywords: Quark model; NN interaction; dressed bag; NN phase shifts; deuteron structure. Two-Component Dressed-Bag Model for NN Interaction 3intermediate ranges ∼ 1-2 fm. This is represented in traditional OBE-models by an effective σ-exchange between free nucleons.Thus, we describe the intermediate-range attraction in the NN sector through an s-channel propagation of an intermediate space-symmetric six-quark bag, stabilized by the scalar-isoscalar σ field. [17][18][19][20] Quite unexpectedly, we discovered that this mechanism of NN interaction, owing to some symmetry properties of the six-quark wavefunctions in initial, intermediate and final states, produces a new tensor force in the NN channel at intermediate range, induced by the intermediate 6q-bag formation. This new force originates entirely from specific symmetry requirements of the 6q wavefunctions and is interrelated tightly with the respective central NN force (both components are being expressed via common vertex factors and propagators). It is very interesting to confront this tensor force induced by the σ-meson generated in the intermediate six-quark bag with the conventional tensor force induced mainly by π-and ρ-meson exchanges in the t-channel between nucleons.Very similarly to the above σ-meson dressing in the six-quark bag, one can consider also π-and ρ-meson dressings with the same s-channel mechanism. This leads to other important implications of the model: • The modified pion cloud of the bag results in new specific e.-m. pair currents which can replace the conventional meson-exchange current terms (e.g. ρπγ) in the treatment of e.-m. effects with large momentum transfer. • The ρ-meson cloud of the bag results quite naturally in an intermediate-range coupling of the total spin (in the NN system and in the bag) with the orbital momentum of the bag and thus leads to an effective intermediate-and short-range new spin-orbit force. It is important to remark in this connection that within the traditional OBE models one uses very high values of cut-off parameters Λ πNN and Λ ρNN to ...

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The Roper resonance is considered as a mixed state of a three-quark core configuration and a hadron molecular component N + σ. Based on this ansatz we study electroproduction of the Roper resonance. The strong and electromagnetic couplings induced by the quark core are calculated in the 3 P0 model. The contribution of the vector meson cloud to the electromagnetic transition is given in the framework of the VMD model. Results are compared with the recent JLab electroproduction data.

A relativistic light-front quark model is used to describe both the elastic nucleon and nucleonRoper transition form factors in a large Q 2 range, up to 35 GeV 2 for the elastic and up to 12 GeV 2 for the resonance case. Relativistic three-quark configurations satisfying the Pauli exclusion principle on the light-front are used for the derivation of the current matrix elements. The Roper resonance is considered as a mixed state of a three-quark core configuration and a molecular N + σ hadron component. Based on this ansatz we obtain a realistic description of both processes, elastic and inelastic, and show that existing experimental data are indicative of a composite structure of the Roper resonance.

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