$\mathbb{Z}_2$-homology of the orbit spaces $G_{n,2}/T^n$
V. Ivanović,
S. Terzić University of Montenegro
Abstract:
We study the
$\mathbb Z_2$-homology groups of the orbit space
$X_n = G_{n,2}/T^n$ for the canonical action of the compact torus
$T^n$ on a complex Grassmann manifold
$G_{n,2}$. Our starting point is the model
$(U_n, p_n)$ for
$X_n$ constructed by Buchstaber and Terzić (2020), where
$U_n = \Delta _{n,2}\times \mathcal{F}_{n}$ for a hypersimplex
$\Delta_{n,2}$ and an universal space of parameters
$\mathcal{F}_{n}$ defined in the works of Buchstaber and Terzić (2019), (2020). It is proved by Buchstaber and Terzić (2021) that
$\mathcal{F}_{n}$ is diffeomorphic to the moduli space
$\mathcal{M}_{0,n}$ of stable
$n$-pointed genus zero curves. We exploit the results of Keel (1992) and Ceyhan (2009) on homology groups of
$\mathcal{M}_{0,n}$ and express them in terms of thestratification of
$\mathcal{F}_{n}$ which are incorporated in the model
$(U_n, p_n)$. In the result we provide the description of cycles in
$X_n$, inductively on
$ n. $ We obtain as well explicit formulas for
$\mathbb Z_2$-homology groups for
$X_5$ and
$X_6$. The results for
$X_5$ recover by different method the results from Buchstaber and Terzić (2021) and Süss (2020). The results for
$X_6$ we consider to be new.
Keywords:
Torus action, Grassmann manifold,spaces of parameters. Received: March 4, 2024Revised: June 23, 2024Accepted: July 3, 2024
DOI:
10.4213/tm4429