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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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We review the application of inverse scattering in nuclear physics. We emphasize the various ways in which inversion can be used to understand nuclear interactions, and survey the results that have been obtained. We discuss S → V inversion from both theoretical and experimentally fitted S-matrices as well as a new method for direct observable →V inversion. The various alternative approaches to inverse scattering are briefly reviewed, and their range of applicability is discussed. This is not a review of formal inversion methods, but the iterative perturbative (IP) approach is described in some detail together with a discussion of the physics results which have been obtained using it and other inversion methods. The case of p+4He scattering is presented in some detail as a case study exemplifying the kind of information which can now be obtained by the application of inverse scattering techniques. It also brings out the comparative properties of different inversion methods.

A new nonconventional mechanism for the basic 2π-fusion reaction pn → d + (ππ)0 in the energy region Tp = 1.0-1.4 GeV is suggested. The mechanism is aimed at providing a consistent explanation for the comprehensive experimental studies of this reaction in exclusive setting done recently by the WASA-at-COSY Collaboration. The basic assumption of the model proposed is the production of the I(J P ) = 0(3 + ) dibaryon resonance D03 in the pn collision. The interference of two decay channels of this resonance: D03 → d + σ → d + (ππ)0 and D03 → D12 + π → d + (ππ)0 is shown to give a strong near-threshold enhancement in the ππ invariant mass spectrum, which is well known as the ABC effect. The σ-meson parameters found to reproduce the ABC enhancement are in a general agreement with models which predict the chiral symmetry restoration at high excitation energy and/or high density of matter, although they are essentially less than those accepted for the free σ meson. So, this result might be considered as an indication of partial chiral symmetry restoration in dense and excited quark matter.The famous Abashian-Booth-Crowe (ABC) effect discovered more than 50 years ago [1] is observed in doublepionic fusion reactions [1-3] as a pronounced spectral enhancement of isoscalar nature just above the ππ-production threshold. The effect was initially interpreted [1] as being due to strong ππ rescattering in the scalar-isoscalar channel, associated naturally with the σ meson. However later on the interpretation was left since no narrow resonance with an appropriate mass (m ≃ 300 MeV) was found in ππ scattering at low energies. At the same time, an other interpretation [4] for the ABC effect, based on a generation of two ∆ isobars via the t-channel meson exchange and their subsequent decays with pion emission, was commonly accepted. Although the "t-channel ∆∆" mechanism did not provide quantitative description of the data, it allowed to reproduce the shape of differential cross sections found in the numerous inclusive experiments on double-pionic fusion [4,5].The situation has changed dramatically quite recently, after publication of the results of the first exclusive and kinematically complete experiments for the basic 2π-fusion reaction pn → d + π 0 π 0 done by the CEL-SIUS/WASA [6] and then by the WASA-at-COSY Collaborations [7]. The comparison of the new experimental data with theoretical predictions has demonstrated clearly that the above t-channel ∆∆ model cannot reproduce even the qualitative behaviour of the experimental energy and angular distributions, giving just a low background in the considered energy region (T p = 1.0-1.4 GeV). At the same time, the most intriguing discovery of these exclusive experiments was an observation of a pronounced resonance structure in the total 2π-production cross section. This fact has been interpreted as a generation of the dibaryon resonance D 03 * Electronic address: platonova@nucl-th.sinp.msu.ru † Electronic address: kukulin@nucl-th.sinp.msu.ru in the pn collision, with quantum number...