The foundations of $(2n,k)$-manifolds

The focus of our paper is a system of axioms that serves as a basis for introducing structural data for $(2n,k)$-manifolds $M^{2n}$, where $M^{2n}$ is a smooth, compact $2n$-dimensional manifold with a smooth effective action of the $k$-dimensional torus $T^k$. In terms of these data a construction of a model space $\mathfrak E$ with an action of the torus $T^k$ is given such that there exists a $T^k$-equivariant homeomorphism $\mathfrak E\to M^{2n}$. This homeomorphism induces a homeomorphism $\mathfrak E/T^k\to M^{2n}/T^k$. The number $d=n-k$ is called the complexity of a $(2n,k)$-manifold. Our theory comprises toric geometry and toric topology, where $d=0$. It is shown that the class of homogeneous spaces $G/H$ of compact Lie groups, where $\operatorname{rk}G=\operatorname{rk}H$, contains $(2n,k)$-manifolds that have nonzero complexity. The results are demonstrated on the complex Grassmann manifolds $G_{k+1,q}$ with an effective action of the torus $T^k$. Bibliography: 23 titles.

toric topology, manifolds with torus action, orbit space, moment map, complex Grassmann manifold