Nuclear vorticity in isoscalar E1 modes: Skyrme-RPA analysis

Abstract

Two basic concepts of nuclear vorticity, hydrodynamical (HD) and Rawenthall-Wambach (RW), are critically inspected. As a test case, we consider the interplay of irrotational and vortical motion in isoscalar electric dipole E1(T=0) modes in 208 Pb, namely the toroidal and compression modes. The modes are described in a self-consistent random-phase-approximation (RPA) with the Skyrme force SLy6. They are examined in terms of strength functions, transition densities, current fields, and formfactors. It is shown that the RW conception (suggesting the upper component of the nuclear current as the vorticity indicator) is not robust. The HD vorticity is not easily applicable either because the definition of a velocity field is too involved in nuclear systems. Instead, the vorticity is better characterized by the toroidal strength which closely corresponds to HD treatment and is approximately decoupled from the continuity equation.

Low-energy dipole excitation modes in $^{10}$Be

“…The toroidal dipole mode is characterized by the vorticity of nuclear current and is the counter part of the standard compressive dipole mode for the IS-GDR as originally proposed by nuclear fluid-dynamics to understand the IS-LED strengths in the stable nuclei [25,26]. In this decade, the vortical nature of the toroidal mode have been microscopically studied with mean-field approaches mainly for spherical nuclei in the heavymass region [27,28,29,30,31,32]. Recently, theoretical studies of the toroidal mode have been extended to deformed nuclei, in which further rich phenomena are expected because of coupling of the LED mode with the nuclear deformation [33,34,35,36,37].…”