Exact Treatment of Continuum Couplings in Nuclear Optical Potentials via Feshbach Theory

Abstract

We present a full-coupling construction of the Feshbach effective interaction in a converged continuum-discretized coupled-channels (CDCC) calculation. The method retains the complete Green's function in the excluded continuum space, treating the continuum-continuum couplings to all orders within the discretized CDCC model space, and therefore yields an explicitly non-local dynamic polarization potential. Applied to $d+^{58}$Ni scattering, the projected two-body potential reproduces the parent CDCC elastic observables and gives a reasonable description of the available experimental data, providing a direct numerical check of the projection. The resulting non-local potential exposes the spatial structure generated by virtual breakup, continuum propagation, and absorption in the continuum. Through the generalized optical theorem, we quantify the continuum-coupling contribution to the elastic flux loss and compare it with the elastic-breakup cross section over a broad incident-energy range. The calculation shows that the elastic-breakup fraction increases with energy, whereas the additional absorption associated with continuum components is strongest at intermediate energies.