  We derive an effective ring model in momentum space for trapped bosons with
synthetic spin-orbit coupling. This effective model is characterized by a
peculiar form of the inter particle interactions, which is crucially modified
by the external confinement. The ring model allows for an intuitive
understanding of the phase diagram of trapped condensates with isotropic
spin-orbit coupling, and in particular for the existence of skyrmion lattice
phases. The model, which may be generally applied for spinor condensates of
arbitrary spin and spin-dependent interactions, is illustrated for the
particular cases of spin-1/2 and spin-1 condensates.

Quantum Gases