title: Ring solitons on vortices.
abstract: Interaction of a ring dark or antidark soliton (RDS and RADS, respectively) with a vortex is considered in the defocusing nonlinear Schrödinger equation with cubic (for RDS) or saturable (for RADS) nonlinearities. By means of direct simulations, it is found that the interaction gives rise to either an almost isotropic or a spiral-like pattern. A transition between them occurs at a critical value of the RDS or RADS amplitude, the spiral pattern appearing if the amplitude exceeds the critical value. An initial ring soliton created on top of the vortex splits into a pair of rings moving inward and outward. In the subcritical case, the inbound ring reverses its polarity, bouncing from the vortex core, without conspicuous effect on the core. In the transcritical case, the bounced ring soliton suffers a spiral deformation, while the vortex changes its position and structure and also loses its axial symmetry. Through a variational-type approach to the system's Hamiltonian, we additionally find that the vortex-RDS and vortex-RADS interactions are, respectively, attractive and repulsive. Simulations with the vortex placed eccentrically with respect to the RDS or RADS reveal the generation of strongly localized multispot dark and/or antidark coherent structures. The occurrence of spiral-like patterns in many numerical experiments prompted an attempt to generate a spiral dark soliton, but the latter is found to suffer a core instability that converts it into a rotating dipole emitting waves in the outward direction.
authors.affiliation: Program in Applied and Computational Mathematics, Princeton University, Fine Hall, Washington Road, Princeton, New Jersey 08544, USA.
authors.forename: P G
authors.initials: PG
authors.lastname: Kevrekidis
authors.forename: H E
authors.initials: HE
authors.lastname: Nistazakis
authors.forename: D J
authors.initials: DJ
authors.lastname: Frantzeskakis
authors.forename: B A
authors.initials: BA
authors.lastname: Malomed
authors.forename: A R
authors.initials: AR
authors.lastname: Bishop