A Classification of Toric, Folded-Symplectic Manifolds

Abstract: Given a $G$-toric, folded-symplectic manifold with co-orientable folding hypersurface, we show that its orbit space is naturally a manifold with corners $W$ equipped with a smooth map $\psi: W \to \frak{g}^*$, where $\frak{g}^*$ is the dual of the Lie algebra of the torus, $G$. The map $\psi$ has fold singularities at points in the image of the folding hypersurface under the quotient map to $W$ and it is a unimodular local embedding away from these points. Thus, to every $G$-toric, folded-symplectic manifold we can associate its orbit space data $\psi:W \to \frak{g}^*$, a unimodular map with folds. We fix a unimodular map with folds $\psi:W \to \frak{g}^*$ and show that isomorphism classes of $G$-toric, folded-symplectic manifolds whose orbit space data is $\psi:W \to \frak{g}^*$ are in bijection with $H^2(W; \mathbb{Z}_G\times \mathbb{R})$, where $\mathbb{Z}_G= \ker(\exp :\mathfrak{g} \to G)$ is the integral lattice of $G$. Thus, there is a pair of characteristic classes associated to every $G$-toric, folded-symplectic manifold. This result generalizes a classical theorem of Delzant, a classification of non-compact toric, symplectic manifolds due to Lerman and Karshon, and the classification of toric, origami manifolds, due to Cannas da Silva, Guillemin, and Pires, in the case where the folding hypersurface is co-orientable.