Bifurcation and global continuation of travelling-rotating Schrödinger maps on the sphere

Abstract

We study travelling-rotating solutions of the Schrödinger map equation into the sphere, viewed as tangent profiles of rigid vortex filaments. Two first integrals reduce the profile equation to a scalar cubic equation for the vertical component, giving an elliptic-function description and explicit closure conditions. We prove bifurcation from the equatorial branch at $\hat{I}{»}_k=R\sqrt{k^2-1}$, $k\ge 2$, and establish a global continuation alternative inside the regular non-polar class. The possible boundary mechanisms are pole contact, vertical collapse, and double-root degeneration. Numerical continuation of the equatorial branches suggests convergence to the north-pole boundary. Up to gauge, the reconstructed vortex filaments are of Kida type.