Realization of GKM fibrations and new examples of Hamiltonian non-K\"ahler actions

Abstract

We classify fibrations of abstract $3$-regular GKM graphs over $2$-regular ones, and show that all fiberwise signed fibrations of this type are realized as the projectivization of equivariant complex rank $2$ vector bundles over quasitoric $4$-folds or $S^4$. We investigate the existence of invariant (stable) almost complex, symplectic, and K\"ahler structures on the total space. In this way we obtain infinitely many K\"ahler manifolds with Hamiltonian non-K\"ahler actions in dimension $6$ with prescribed one-skeleton, in particular with prescribed number of isolated fixed points.