Links between the integrable systems of CMC surfaces, isothermic surfaces and constrained Willmore surfaces

Abstract: Since constant mean curvature surfaces in 3-space are special cases of isothermic and constrained Willmore surfaces, they give rise to three, apriori distinct, integrable systems. We provide a comprehensive and unified view of these integrable systems in terms of the associated families of flat connections and their parallel sections: in case of a CMC surface, parallel sections of all three associated families of flat connections are given algebraically by parallel sections of either one of the families. As a consequence, we provide a complete description of the links between the simple factor dressing given by the conformal Gauss map, the simple factor dressing given by isothermicity, the simple factor dressing given by the harmonic Gauss map, as well as the relationship to the classical, the $\mu$- and the $\varrho$-Darboux transforms of a CMC surface. Moreover, we establish the associated family of the CMC surfaces as limits of the associated family of isothermic surfaces and constrained Willmore surfaces.