Let $V$ be an $n$-dimensional vector space over the finite field of order $q$. The spherical building $X_V$ associated with $GL(V)$ is the order complex of the nontrivial linear subspaces of $V$. Let $\mathfrak{ g}$ be the local coefficient system on $X_V$, whose value on the simplex $\sigma=[V_0 \subset \cdots \subset V_p] \in X_V$ is given by $\mathfrak{ g}(\sigma)=V_0$. Following the work of Lusztig and Dupont, we study the homology module $D^k(V)=\tilde{ H}_{ n-k-1}(X_V;\mathfrak{ g})$. Our results include a construction of an explicit basis of $D^1(V)$, and the following twisted analogue of a result of Smith and Yoshiara: For any $1 \leq k \leq n-1$, the minimal support size of a non-zero $(n-k-1)$-cycle in the twisted homology $\tilde{ H}_{ n-k-1}(X_V;\wedge^k \mathfrak{ g})$ is $\frac{ (n-k+2)!}{ 2}$.
Categories: math.CO