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

TL;DR

This paper introduces a numerically exact method combining Feshbach theory and CDCC to derive precise nuclear optical potentials, accurately capturing continuum effects and improving reaction predictions for weakly bound nuclei.

Contribution

The authors develop the first exact numerical implementation of full continuum coupling in nuclear optical potentials, surpassing previous weak-coupling approximations.

Findings

Exact potentials reproduce CDCC observables precisely.

Weak-coupling and folding models show significant deviations.

The method enables separation of elastic breakup from fusion processes.

Abstract

We present the first numerically exact implementation of full-coupling Feshbach theory for deriving effective optical potentials in nuclear reactions, overcoming long-standing computational barriers that previously necessitated weak-coupling approximations. By integrating Feshbach projection operators with the Continuum-Discretized Coupled-Channels (CDCC) method, we rigorously incorporate all continuum-continuum interactions, previously considered intractable, to extract dynamic polarization potentials that capture virtual excitations and absorption in reactions with weakly bound nuclei. Application to deuteron-induced reactions on $^{58}$Ni demonstrates that our full-coupling effective potentials reproduce CDCC observables exactly, while weak-coupling and folding-model approaches show significant deviations. The method uniquely separates elastic breakup from breakup-fusion processes through the optical theorem, enabling precise determination of incomplete and complete fusion cross sections, critical for interpreting rare-isotope beam experiments at facilities like FRIB. The non-local polarization potentials provide insights into the energy-dependent interplay between reaction mechanisms, with our analysis suggesting an increasing relative importance of elastic breakup at higher energies while continuum absorption shows more complex behavior. This exact treatment eliminates systematic uncertainties from coupling approximations, providing predictive power for unstable nuclei far from stability where experimental data are scarce.