Coulomb bridge mechanism for peripheral polarization of weakly bound projectiles

Abstract

We identify the matrix elements that carry peripheral polarization of weakly bound projectiles through the Feshbach dynamical polarization potential (DPP) within the continuum-discretized coupled-channels (CDCC) framework. Splitting the two P-Q bridge couplings into nuclear and Coulomb parts, while keeping a single Q-space propagator common to every term, decomposes the DPP into a nuclear, a Coulomb, and an interference component, $\Delta U_{\mathrm{DPP}}=\Delta U_N+\Delta U_C+\Delta U_{NC}$. Applied to $d+{}^{58}$Ni, ${}^6$Li$+{}^{208}$Pb, ${}^{11}$Be$+{}^{64}$Zn, and ${}^8$B$+{}^{64}$Zn, the decomposition reveals a controlled hierarchy: a nuclear bridge in the light system, a mixed bridge with strong destructive interference in the heavy stable case, and a Coulomb-dominated bridge in both halo systems, with the proton halo showing constructive nuclear-Coulomb interference. For the halo reactions, peripheral partial waves ($L\gtrsim 35$) satisfy ${\sigma }_R^L\simeq {\sigma }_{\mathrm{DPP}}^L\simeq {\sigma }_{\mathrm{BU}}^L$, with the high-$L$ DPP tail dominated by ${\sigma }_C^L$. Two diagnostic calculations isolate the responsible matrix elements: removing the off-diagonal Coulomb propagation inside Q leaves the pattern essentially intact, whereas removing the Coulomb part of the P-Q bridge collapses both DPP-induced absorption and breakup. The peripheral polarization of halo reactions is therefore a Coulomb-bridge effect, and the high-$L$ elastic-breakup yield serves as its observable signature.