## Osaka Journal of Mathematics

### On the cohomology of torus manifolds

#### Abstract

A torus manifold is an even-dimensional manifold acted on by a half-dimensional torus with non-empty fixed point set and some additional orientation data. It may be considered as a far-reaching generalisation of toric manifolds from algebraic geometry. The orbit space of a torus manifold has a rich combinatorial structure, e.g., it is a manifold with corners provided that the action is locally standard. Here we investigate relationships between the cohomological properties of torus manifolds and the combinatorics of their orbit quotients. We show that the cohomology ring of a torus manifold is generated by two-dimensional classes if and only if the quotient is a homology polytope. In this case we retrieve the familiar picture from toric geometry: the equivariant cohomology is the face ring of the nerve simplicial complex and the ordinary cohomology is obtained by factoring out certain linear forms. In a more general situation, we show that the odd-degree cohomology of a torus manifold vanishes if and only if the orbit space is face-acyclic. Although the cohomology is no longer generated in degree two under these circumstances, the equivariant cohomology is still isomorphic to the face ring of an appropriate simplicial poset.

#### Article information

Source
Osaka J. Math., Volume 43, Number 3 (2006), 711-746.

Dates
First available in Project Euclid: 25 September 2006

https://projecteuclid.org/euclid.ojm/1159190010

Mathematical Reviews number (MathSciNet)
MR2283418

Zentralblatt MATH identifier
1111.57019

Subjects
Primary: 57R91: Equivariant algebraic topology of manifolds

#### Citation

Masuda, Mikiya; Panov, Taras. On the cohomology of torus manifolds. Osaka J. Math. 43 (2006), no. 3, 711--746. https://projecteuclid.org/euclid.ojm/1159190010

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