V. N. Pomerantsev

Detailed study of the cluster structure of light nuclei in a three-body model (IV). Large space calculation for A = 6 nuclei with realistic nuclear forces☆

Abstract The structure of all low-lying states for the A = 6 nuclei ( 6 He, 6 Li, 6 Be) is described in detail in terms of a realistic three-body α + 2N model using the full Reid soft-core NN potential (RSC), the accurate Nα interaction potential with odd-even splitting in central and spin-orbital components and the exact RGM Pauli projectors onto forbidden 0s-states in five-nucleon subsystems. The model thus includes all necessary types of forces: central, spin-orbital, tensor, Coulomb and partial exchange. The new refined version of the model gives a good agreement with experiment without any free parameters for all static characteristics of A = 6 nuclei (except for the 6 Li quadrupole moment), for the 6 Li electromagnetic form factors, for the Coulomb displacements of the 0 + 1 and 2 + 1 levels of three 6 He, 6 Li, 6 Be nuclei, for the 6 He β-decay probability and for the γ-widths of the 6 Li excited states. An analysis of the geometric shapes of low-lying states of 6 He, 6 Li, 6 Be nuclei is given.

The orthogonal projection method in scattering theory

Abstract This work gives a detailed account of the orthogonal projection method in the theory of two- and three-body scattering, which is based on the employment of orthogonal projecting pseudopotentials. The method is applied to a number of physical problems, of which the following the most important: the improvement of convergence and the rearragement of Born series to make them convergent at low energies in the presence of bound states in a system, as well as the consideration of the Pauli exclusion principle in the scattering of composite particles and in the integral theory of direct nuclear reactions. The properties of eigenvalues of kernels of the equations obtained are investigated and the conditions for the convergence of their iterations are derived. For the three-body problem, the general case of three different particles is considered, as well as two particular cases, namely, two particles in the field of a heavy core and three identical particles. The proven theorems are illustrated by numerical examples. Other useful applications of the proposed approach are listed and discussed, in particular, those in solid-state physics and in the theory of electromagnetic transitions. The approach suggested is compared with those of the other authors and the prospects of using the developed formalism are discussed.

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.

Moscow-type NN potentials and three-nucleon bound states

A detailed description of Moscow-type (M-type) potential models for the NN interaction is given. The microscopic foundation of these models, which appear as a consequence of the composite quark structure of nucleons, is discussed. M-type models are shown to arise naturally in a coupled channel approach when compound or bag-like six-quark states, strongly coupled to the NN channel, are eliminated from the complete multiquark wave function. The role of the deep-lying bound states that appear in these models is elucidated. By introducing additional conditions of orthogonality to these compound six-quark states, a continuous series of almost on-shell equivalent nonlocal interaction models, characterized by a strong reduction or full absence of a local repulsive core (M-type models), is generated. The predictions of these interaction models for 3N systems are analyzed in detail. It is shown that M-type models give, under certain conditions, a stronger binding of the 3N system than the original phase-equivalent model with nodeless wave functions. An analysis of the 3N system with the new versions of the Moscow NN potential describing also the higher even partial waves is presented. Large deviations from conventional NN force models are found for the momentum distribution in the high momentum region. In particular, the Coulomb displacement energy for nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H binding energy is extrapolated to the experimental value.

The properties of the three-nucleon system with the dressed-bag model for NN interaction: I. New scalar three-body force

A multi-component formalism is developed to describe three-body systems with nonstatic pairwise interactions and non-nucleonic degrees of freedom. The dressed-bag model for NN interaction based on the formation of an intermediate six-quark bag dressed by a σ-field is applied to the 3N system, which results in a new three-body force between the six-quark bag and a third nucleon. Concise variational calculations of 3N bound states are carried out in the dressed-bag model including the new three-body force. It is shown that this three-body force gives at least half the 3N total binding energy, while the weight of non-nucleonic components in the 3 H and 3 He wavefunctions can exceed 10%. The new force model provides a very good description of 3N bound states with a reasonable magnitude of the aNN coupling constant. The model can serve as a natural bridge between dynamical description of few-nucleon systems and the very successful Walecka approach to heavy nuclei and nuclear matter.

The NN-potential with forbidden state suggested from a six-quark model with one-pion exchange

Abstract A new, realistic NN-potential is proposed which is suggested from a six-quark model with dominant quark configuration s4p2 and includes the one-pion exchange mechanism in the 1S0 and coupled 3S1 − 3D1 channels. The potential is purely attractive on the mass shell and includes a deep-lying forbidden state instead of a repulsive core. A very small number of free parameters is sufficient to succesfully describe both the 3S1 − 3D1 NN-phase shifts, the mixing parameter e and the singlet 1S0 phase shifts in a broad energy range from 0 to 400 MeV (alongside with effective range parameters) and also basic deuteron parameters (i.e. binding energy, RMS charge radius, quadrupole moment, etc.). The deuteron wave function components (u and w) have an inner node at the place of the hard core of the conventional realistic NN potentials.

The deuteron structure and NN-phase shifts for realistic local superdeep NN-potential with an extra state

Abstract The deutron structure and NN-phase shifts for triplet- and singlet-even states are studied in terms of a new model for an attractive local deep NN-potential with an extra state. The model is shown to permit a simultaneous and high-accuracy description of all the deuteron parameters, except the magnetic moment, and the behaviour of the longitudinal, A(q2), and transversal, B(q2), deuteron form factors in a broad range of transferred momenta. The deuteron wavefunction in the model is strongly enriched with high-momentum components and tabulated in a convenient form.

Experimental and theoretical indications for an intermediate σ-dressed dibaryon in the NN interaction

Abstract Numerous theoretical and experimental arguments in favor of the generation of intermediate σ-dressed dibaryon in NN interaction at middle and short distances are presented. We argue that this intermediate dibaryon should be responsible for the strong middle-range attraction and the short-range repulsion in the NN interaction, and also for the short-range correlations in nuclei. The suggested mechanism for the σ-dressing of the dibaryon is identical to that which explains the Roper-resonance structure, its dominant decay mode and its extraordinary low mass. It is arguing that the (partial) chiral symmetry restoration effects, common for the Roper resonance and dressed dibaryon, are responsible for strong renormalizing of their masses and widths and the observed σ-meson mass and decay width as well. The new experimental data on 2π-production in the scalar–isoscalar channel produced in pn- and pd-collisions and recent data on γγ correlations in pC and dC scattering in the GeV region seems to corroborate the existence of the σ-dressed dibaryon in two- and three-nucleon interactions. A similar transformation mechanism from the glue to the scalar field can be valid also in some J/Ψ decays and in enormous σ-meson production in central pp collisions at high energies.

Stark transitions and elastic scattering of excited muonic hydrogen

The quantum mechanical approach for the description of Stark mixing and elastic scattering of excited muonic hydrogen in collision with hydrogen atoms is developed in the adiabatic approximation. For principal quantum number ⩽12 and collision energies 0.1 ⩽E⩽10 eV the partial σn(l → l′;E), total σn(l;E) andl-averaged σn(E) cross sections are calculated. The differential and transport cross sections for the elastic scattering are also obtained.

Solving three-body scattering problems in the momentum lattice representation

A brief description of the novel approach toward solving few-body scattering problems in a finite-dimensional functional space of the L{sub 2} type is presented. The method is based on the complete few-body continuum discretization in the basis of stationary wave packets. This basis, being transformed to the momentum representation, leads to the cell-lattice-like discretization of the momentum space. So the initial scattering problem can be formulated on the multidimensional momentum lattice, which makes it possible to reduce the solution of any scattering problem above the breakup threshold (where the integral kernels include, in general, some complicated moving singularities) to convenient simple matrix equations that can be solved on the real energy axis. The phase shifts and inelasticity parameters for the three-body nd elastic scattering with MT I-III NN potential both below and above the three-body breakup threshold calculated with the proposed wave-packet technique are in a very good agreement with the previous accurate benchmark calculation results.