Kähler complexity one Hamiltonian $T$-manifolds have trivial paintings

Abstract

Let a torus $T$ act on a symplectic manifold $(M,\omega )$ with moment map $\varphi$. We say that the Hamiltonian $T$-manifold $(M,\omega ,\varphi )$ has complexity one if $\frac{1}{2}\dim M-\dim T=1$, and that it is Kähler if it admits an invariant compatible complex structure. In this paper, we show how the class of Kähler complexity one Hamiltonian $T$-manifolds sits inside the class of complexity one Hamiltonian $T$-manifolds by proving that every compact, connected Kähler complexity one Hamiltonian $T$-manifold has a trivial painting. As a corollary, we show that two tall compact, connected Kähler complexity one Hamiltonian $T$-manifolds are symplectomorphic exactly if they have the same genus, Duistermaat-Heckman measure, and skeleton. Here, $(M,\omega ,\varphi )$ is tall exactly if every non-empty fiber ${\varphi }^{-1}(\alpha )$ contains more than one orbit.

15 pages