I. T. Obukhovsky

On magnetic colour attraction in the NN system

Abstract Magnetic colour NN attraction arises if the nodeless NN wave function φ(RNN) is substituted by a function with one node. The latter corresponds to the quark configuration (1 s ) 4 (1 p ) 2 , [ƒ] X = [42], [ƒ] CS = [42] with the predominance of symmetric qq pairs in the CS space. As a result, the increased kinetic energy is roughly compensated and the quark configurations (1s)6 and (1s)4(1p)2(become approximately degenerate.

New mechanism for intermediate- and short-range nucleon-nucleon interaction

For the intermediate- and short-range part of the nucleon-nucleon interaction a new approach is suggested based on the formation of a symmetric six-quark bag in the state |(0s)6[6]X,L = 0 dressed due to strong coupling to π, σ and ρ fields (dressed bag). This new mechanism offers both a strong intermediate-range attraction which replaces the effective σ-exchange (or excitation of two isobars in the intermediate state) in traditional force models and also short-range repulsion. Part of the intermediate and the full long-range contribution to the nucleon-nucleon force is also in this approach described by the Yukawa meson-exchange mechanism. A simple illustrative model is developed which demonstrates clearly how well the suggested new mechanism can reproduce the NN data.

The nucleon-nucleon scattering and the baryon spectrum in the quark cluster model with two scales of interaction

Abstract The potential model which includes colour exchange interactions as well as π-and σ-exchanges at the quark level, is used to describe the baryon spectrum and the NN scattering data in the wide interval 0 E lab ⪅1 GeV. A modification of the resonating group method is suggested, which allows for the quark configurations s 6 and s 4 p 2 in the overlap region, and in this context the problem of the repulsive core is discussed.

The 12C nucleus as a 3α system with forbidden states

Abstract We have calculated the 0 1 + ground state and the 0 2 + and 0 3 + first excited states of 12 C in the model of three α-particles whose interaction is described using a local attractive potential with forbidden states, which well reproduces the α-α scattering phases. The methods of projection of the states forbidden by the Pauli exclusion principle in a system of three composite particles are discussed. The results of the calculation show that the condition of orthogonality to the forbidden states is sufficient to prevent the system from collapse. The binding energy value obtained (15.06 MeV) is somewhat overestimated. This discrepancy seems to come from neglecting triple exchanges of nucleons of different α-particles and from the fact that the 12 C real nucleus differs from the 3α system.

Electroproduction of the Roper resonance on the proton: the role of the three-quark core and the molecular

The Roper resonance is considered as a mixed state of a three-quark core configuration and a hadron molecular component N+sigma. 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 3P0 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.

N\sigma

A method for calculating the fractional parentage coefficients for many-quark systems in the scheme UCST(12) contains/implies UCS(6)*UT(2) contains/implies UC(3)*US(2)*UT(2) based on the complementarity of the permutation SN and unitary U(n) groups, is developed. The scalar factors of the Clebsch Gordan coefficients for the chain of groups U(mn) contains/implies U(m)*U(n) are shown to be independent of the ranks mn, and m and n of the groups and to be determined by the Young schemes associated with them. Tables of fractional parentage coefficients for low states of the six-quark (6q) system are presented.

component

A relativistic light-front quark model is used to describe both the elastic nucleon and nucleon-Roper transition form factors in a large Q2 range, up to 35 GeV2 for the elastic and up to 12 GeV2 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+sigma 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.

On the construction of wavefunctions in the six quark system

The impact of the short-range NΔ interaction on the pion photoproduction processes off the deuteron in the Δ-resonance region is studied in the framework of a recently proposed dressed-bag model. A common dressing procedure for bare three- and six-quark states is used to describe both the pion decay widths of baryon resonances and the effective NN (or NΔ) interaction at short ranges. It is shown that the effect of short-range NΔ interaction for the forward-angle π0 photoproduction off the deuteron cannot be neglected. The prospects for further development of the model to describe the short-range NN (or NΔ) correlations in the lightest nuclei are discussed.

Electromagnetic structure of the nucleon and the Roper resonance in a light-front quark approach

The spectrum and eigenfunctions of deuteronlike states in the quark bag for the configurationsS6 andS4P2 have been studied. The complete tables of the fractional parentage coefficients (f.p.c.) for these configurations in thej-j andL-S coupling schemes are presented. The universal method of calculation of the f.p.c. which is based on the complementarity of the unitary and permutation group, is considered. The method enable one to calculate the Clebsh-Gordon coefficients and the invariant symbols of the noted groups. It is shown that the lowest energy state of the configurationS12/4P32/2 resembles the partial wave3D1 and can, therefore, be coupled to it in a deuteron. On the contrary, the lowest states in the configurationsS12/6 andS12/4P12/2 resemble the3S1-wave.

A dressed-bag model study of the short-range NΔ interaction in pion photoproduction processes off the deuteron

Abstract The interference term between s - and t -pole contributions to the p ( e , e ′ π + ) n cross section is evaluated on the basis of the constituent quark model. It is shown that the contribution of baryon s -poles can be modeled by a nonlocal extension of the Kroll–Ruderman contact term. This contribution is in a destructive interference with the pion t -pole that is essential to improve the description of recent JLab data at the invariant mass W = 1.95 GeV . Some predictions are made for a new JLab measurement at higher values W = 2.1 – 2.3 GeV and Q 2 centered at 1.6 and 2.45 GeV 2 / c 2 .