Algebraic Model for Quantum Scattering. Reformulation, Analysis and Numerical Strategies

The convergence problem for scattering states is studied in detail within the framework of the Algebraic Model, a representation of the Schrodinger equation in an L^2 basis. The dynamical equations of this model are reformulated featuring new "Dynamical Coefficients", which explicitly reveal the potential effects. A general analysis of the Dynamical Coefficients leads to an optimal basis yielding well converging, precise and stable results. A set of strategies for solving the equations for non-optimal bases is formulated based on the asymptotic behaviour of the Dynamical Coefficients. These strategies are shown to provide a dramatically improved convergence of the solutions.Comment: 31 pages, 41 postscript figure

Theoretical analysis of resonance states in 4H^{4}H, 4He^{4}He and 4Li^{4}Li above three-cluster threshold

The resonance states of $^{4}H$, $^{4}He$ and $^{4}Li$, embedded in the three-cluster $d+N+N$ continuum, are investigated within a three-cluster model. The model treats the Pauli principle exactly and incorporates the Faddeev components for proper description of the boundary conditions for the two- and three-body continua. The hyperspherical harmonics are used to distinguish and numerate channels of the three-cluster continuum. It is shown that the effective barrier, created by three-cluster configuration $d+N+N$, is strong enough to accommodate two resonance states.Comment: 20 page, 4 figure

Monopole and quadrupole polarization effects on the alpha-particle description of 8^{8}Be

We investigate the effect of monopole and quadrupole modes on the elastic alpha-alpha resonance structure of $^{8}$Be. To this end we make a fully microscopic coupled channels calculation with three coupled channels, using the Algebraic Model. The continuum spectrum and wave functions are analyzed in terms of the individual channels to understand the nature of the resonances. It is shown that both monopole and quadrupole modes have a non-negligible effect on the resonances in the alpha-alpha continuum.Comment: 20 pages, 4 figures. submitted to Phys.Rev.

Algebraic Model for scattering of three-s-cluster systems; 2, Resonances in the three-cluster continuum of 6He and 6Be

The resonance states embedded in the three-cluster continuum of 6He and 6Be are obtained in the Algebraic Version of the Resonating Group Method. The model accounts for a correct treatment of the Pauli principle. It also provides the correct three-cluster continuum boundary conditions by using a Hyperspherical Harmonics basis. The model reproduces the observed resonances well and achieves good agreement with other models. A better understanding for the process of formation and decay of the resonance states in six-nucleon systems is obtained

Algebraic Model for scattering of three-s-cluster systems. II. Resonances in the three-cluster continuum of 6He and 6Be

The resonance states embedded in the three-cluster continuum of 6He and 6Be are obtained in the Algebraic Version of the Resonating Group Method. The model accounts for a correct treatment of the Pauli principle. It also provides the correct three-cluster continuum boundary conditions by using a Hyperspherical Harmonics basis. The model reproduces the observed resonances well and achieves good agreement with other models. A better understanding for the process of formation and decay of the resonance states in six-nucleon systems is obtained.Comment: 8 pages, 10 postscript figures, submitted to Phys. Rev.

Algebraic Model for scattering in three-s-cluster systems. I. Theoretical Background

A framework to calculate two-particle matrix elements for fully antisymmetrized three-cluster configurations is presented. The theory is developed for a scattering situation described in terms of the Algebraic Model. This means that the nuclear many-particle state and its asymptotic behaviour are expanded in terms of oscillator states of the intra-cluster coordinates. The Generating Function technique is used to optimize the calculation of matrix elements. In order to derive the dynamical equations, a multichannel version of the Algebraic Model is presented.Comment: 20 pages, 1 postscript figure, submitted to Phys. Rev.

A Microscopic Cluster Description of 12C

We investigate both bound and resonance states in 12C embedded in a three-\alpha-cluster continuum using two distinct three-cluster microscopic models. The first one relies on the Hyperspherical Harmonics basis to enumerate the channels describing the three-cluster continuum. The second model incorporates both Gaussian and Oscillator basis functions, and reduces the three-cluster problem to a two-cluster one, in which a two-cluster subsystem is described by a set of pseudo-bound state states. It is shown that the results agree well with comparable calculations from the literature.Comment: 31 pages, 12 figures, 9 table