Global Solutions to the 3D Half-Wave Maps Equation with Angular Regularity

Abstract: The half-wave maps equation is a nonlocal geometric equation arising in the continuum dynamics of Haldane-Shashtry and Calogero-Moser spin systems. In high dimensions $n\geq4$, global wellposedness for data which is small in the critical Besov space $\dot{B}^{n/2}_{2,1}$ is known since the works of Krieger, Sire and Kiesenhofer [13,9]. There is a major obstruction in extending these results to three dimensions due to the loss of the crucial $L^2_tL^\infty_x$ Strichartz estimate. In this work, we make progress on this case by proving that the equation is "weakly" globally well-posed (in the sense of Tao [28]) for initial data which is not only small in $\dot{B}^{3/2}_{2,1}$ but also possesses some angular regularity and weighted decay of derivatives. We use Sterbenz's improved Strichartz estimates in conjunction with certain commuting vector fields to develop trilinear estimates in weighted Strichartz spaces which avoid the use of the $L^2_tL^\infty_x$ endpoint.