Breakup Amplitudes from the Pseudostate Extension of the Coupled-Reaction-Channels Method

A pseudochannel extension of the coupled-reaction-channel (CRC) ansatz had been used in earlier work to simulate the effect of the breakup channel on the rearrangement amplitudes. Comparisons with benchmark results on model systems established that rearrangement amplitudes and total breakup probability could be obtained accurately. However, achieving the same level of accuracy with respect to the state-to-state breakup amplitudes had eluded the earlier attempts that used global bases to generate the pseudo states. With the global bases it is difficult to control the spectrum of pseudostate energies and to obtain an optimal distribution of these pseudo-levels. In the present work, local bases in momentum space of the type used in Finite Element methods are employed. Pseudostates are generated using a local interpolation basis in the relative momentum of the two-body subsystem. Local nature of such a basis allows us to control the density of two-body pseudostates by simply adjusting the distribution of the grid points. In the present work, it is demonstrated that breakup amplitudes can be extracted quantitatively using pseudostates generated from a basis of local piecewise quadratic interpolation polynomials. For a local-potential s-wave model of the n+d scattering, state-to-state breakup amplitudes obtained from the present approach are compared with the benchmark results available in the literature. Results further confirm that pseudostate-extended CRC method is a viable and efficient approach for three-particle scattering.