Analysis of the 6^6He β\beta decay into the α+d\alpha+d continuum within a three-body model

The beta-decay process of the $^6$He halo nucleus into the alpha+d continuum is studied in a three-body model. The $^6$He nucleus is described as an alpha+n+n system in hyperspherical coordinates on a Lagrange mesh. The convergence of the Gamow-Teller matrix element requires the knowledge of wave functions up to about 30 fm and of hypermomentum components up to K=24. The shape and absolute values of the transition probability per time and energy units of a recent experiment can be reproduced very well with an appropriate alpha+d potential. A total transition probability of 1.6E-6 s$^{-1}$ is obtained in agreement with that experiment. Halo effects are shown to be very important because of a strong cancellation between the internal and halo components of the matrix element, as observed in previous studies. The forbidden bound state in the alpha+d potential is found essential to reproduce the order of magnitude of the data. Comments are made on R-matrix fits.Comment: 18 pages, 9 figures. Accepted for publication in Phys.Rev.

A unique decay process: beta delayed emission of a proton and a neutron by the 11^{11}Li halo nucleus

The neutron-rich $^{11}$Li halo nucleus is unique among nuclei with known separation energies by its ability to emit a proton and a neutron in a $\beta$ decay process. The branching ratio towards this rare decay mode is evaluated within a three-body model for the initial bound state and with Coulomb three-body final scattering states. The branching ratio should be comprised between two extreme cases, i.e.\ a lower bound $6 \times 10^{-12}$ obtained with a pure Coulomb wave and an upper bound $5 \times 10^{-10}$ obtained with a plane wave. A simple model with modified Coulomb waves provides plausible values between between $0.8 \times 10^{-10}$ and $2.2 \times 10^{-10}$ with most probable total energies of the proton and neutron between 0.15 and 0.3 MeV.Comment: 15 pages, 3 figure

Phase equivalent potentials for three-body halos

We compare the properties of three-body systems obtained with two-body potentials with Pauli forbidden states and with the corresponding phase equivalent two-body potentials. In the first case the forbidden states are explicitly excluded in the calculation. Differences arise due to the off-shell properties of these on-shell equivalent potentials. We use the adiabatic hyperspherical method to formulate a practical prescription to exclude Pauli forbidden states in three-body calculations. Schematic as well as realistic potentials are used. Almost indistinguishable results are obtained.Comment: 18 pages, 6 figure

Multichannel coupling with supersymmetric quantum mechanics and exactly-solvable model for Feshbach resonance

A new type of supersymmetric transformations of the coupled-channel radial Schroedinger equation is introduced, which do not conserve the vanishing behavior of solutions at the origin. Contrary to usual transformations, these ``non-conservative'' transformations allow, in the presence of thresholds, the construction of potentials with coupled scattering matrices from uncoupled potentials. As an example, an exactly-solvable potential matrix is obtained which provides a very simple model of Feshbach-resonance phenomenon.Comment: 10 pages, 2 figure

Exact Soliton-like Solutions of the Radial Gross-Pitaevskii Equation

We construct exact ring soliton-like solutions of the cylindrically symmetric (i.e., radial) Gross- Pitaevskii equation with a potential, using the similarity transformation method. Depending on the choice of the allowed free functions, the solutions can take the form of stationary dark or bright rings whose time dependence is in the phase dynamics only, or oscillating and bouncing solutions, related to the second Painlev\'e transcendent. In each case the potential can be chosen to be time-independent.Comment: 8 pages, 7 figures. Version 2: stability analysis of the dark solutio

Crossover from one to three dimensions for a gas of hard-core bosons

We develop a variational theory of the crossover from the one-dimensional (1D) regime to the 3D regime for ultra-cold Bose gases in thin waveguides. Within the 1D regime we map out the parameter space for fermionization, which may span the full 1D regime for suitable transverse confinement.Comment: 4 pages, 2 figure

11Li beta decay into 9Li and deuteron within a three-body model

The beta decay process of the 11Li halo nucleus into 9Li and d is studied in a three-body model. The 11Li nucleus is described as a 9Li+n+n system in hyperspherical coordinates on a Lagrange mesh. Various 9Li+d potentials are compared involving a forbidden state, a physical bound state, and a resonance near 0.25 MeV in the s-wave. With an added surface absorption, they are compatible with elastic scattering data. The transition probability per time unit is quite sensitive to the location of the resonance. For a fixed resonance location, it does not depend much on the potential choice at variance with the 6He delayed deuteron decay. The calculated transition probability per time unit is larger than the experimental value but the difference can be explained by a slightly higher resonance location and/or by absorption from the 9Li+d final channel.Comment: 14 pages, 7 figures, 3 table