Orbital stability for the equivariant Chern--Simons gauged Landau--Lifshitz equation in $\mathbb{R}^2$

Abstract

We study the equivariant Chern--Simons gauged Landau--Lifshitz equation in $\mathbb R^2$. For equivariance index $m\ge2$ and a potential $V\in C^{3,1}([0,2])$ satisfying $V(0)=V'(0)=0$, we first establish local well-posedness for the Cauchy problem at the $H^2$ level, with the sphere constraint written in the natural affine space $u-\vec n\in H^2$. For nonnegative $V$ we then consider an $m$--equivariant ground state of $H_ω=E+ωM$, $ω>0$. Under a constrained nondegeneracy condition for the polar Hessian, the conserved energy and mass give orbital stability in $H^1$. A Gustafson--Shatah type continuation argument, in which the Chern--Simons feedback is treated as a tame nonlocal zeroth-order perturbation, upgrades this conditional stability to global $H^2$ existence for all $H^2$ initial data sufficiently close to the ground state orbit in $H^1$. For the quadratic potential we also verify the nondegeneracy condition in a nonempty interior near-BPS regime approaching the self-dual point $(κ,ω)=(1,0)$. This yields a concrete family of globally defined orbitally stable ground states.