Generalized Skyrme crystals

This Letter deals with triply-periodic (crystalline) solutions in a family of Skyrme systems, namely where the field takes values in the squashed 3-sphere. The family includes the standard Skyrme model (round 3-sphere), and the Skyrme-Faddeev case (maximal squashing). In the round case, the lowest-energy crystal is the well-known cubic lattice of half-skyrmions; but in the squashed case the minimal-energy crystal structures turn out to be different. We describe some of the solutions that arise, including arrays of vortices and multi-sheeted structures.