On Fixed-Point Sets of $\Z_2$-Tori in Positive Curvature

TL;DR

This paper extends the understanding of fixed point sets of $ ext{Z}_2$-tori in positively curved manifolds, lowering rank bounds and classifying cohomology rings of fixed point components.

Contribution

It improves previous bounds on the rank of $ ext{Z}_2$-tori and classifies the cohomology rings of their fixed point sets in positively curved manifolds.

Findings

Lowered rank bounds to approximately n/6 and n/8.

Classified the cohomology rings of fixed point sets.

Extended previous symmetry results to $ ext{Z}_2$-tori.

Abstract

In recent work of Kennard, Khalili Samani, and the last author, they generalize the Half-Maximal Symmetry Rank result of Wilking for torus actions on positively curved manifolds to $\mathbb{Z}_2$-tori with a fixed point. They show that if the rank is approximately one-fourth of the dimension of the manifold, then fixed point set components of small co-rank subgroups of the $\Z_2$-torus are homotopy equivalent to spheres, real projective spaces, complex projective spaces, or lens spaces. In this paper, we lower the bound on the rank of the $\mathbb{Z}_2$-torus to approximately $n/6$ and $n/8$ and are able to classify either the integral cohomology ring or the $\mathbb{Z}_2$-cohomology ring, respectively, of the fixed point set of the $\mathbb{Z}_2$-torus.