Effects of velocity-dependent and spin-orbit terms of the Skyrme interaction on non-locality parameter of microscopic optical potentials

Tóm tắt

We investigate how the velocity-dependent (t₁ and t₂) and spin-orbit (W₀) terms of the Skyrme effective interaction influence the non-locality parameter β of the microscopic optical potential (MOP) for neutron elastic scattering off the doubly closed-shell nuclei ¹⁶O, ⁴⁰Ca, ⁴⁸Ca, and ²⁰⁸Pb at incident energies below 20 MeV. The MOP is constructed within the particle-vibration coupling framework on top of self-consistent Hartree-Fock plus random-phase approximation calculations by using the SLy5 parametrisation. Three calculation schemes are compared: the full Skyrme interaction, the interaction without t₁ and t₂, and the interaction without W₀ in the residual interaction. The velocity-dependent terms exert a pronounced and mass-dependent influence on β: removing them increases β_v by 0.27 fm for ¹⁶O but decreases it by 0.50 fm for ²⁰⁸Pb. The spin-orbit term, by contrast, produces much weaker modifications, typically below 0.1 fm. The extracted β values lie in the range 0.70–1.43 fm, with most values exceeding the widely adopted Perey-Buck value of 0.85 fm, suggesting that this empirical parameter underestimates the true microscopic non-locality for most nuclei.