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Periodicity in the cohomology of finite general linear groups via 𝑞-divided powers
Transactions of the American Mathematical Society ( IF 1.3 ) Pub Date : 2021-05-07 , DOI: 10.1090/tran/8383
Rohit Nagpal , Steven V Sam , Andrew Snowden

Abstract:We show that $\bigoplus _{n \ge 0} \mathrm {H}^t(\mathbf {GL}_{n}(\mathbf {F}_q), \mathbf {F}_{\ell })$ canonically admits the structure of a module over the $q$-divided power algebra (assuming $q$ is invertible in $\mathbf {F}_{\ell }$), and that, as such, it is free and (for $q \neq 2$) generated in degrees $\le t$. As a corollary, we show that the cohomology of a finitely generated $\mathbf {VI}$-module in non-describing characteristic is eventually periodic in $n$. We apply this to obtain a new result on the cohomology of unipotent Specht modules.


中文翻译:

通过𝑞-除幂的有限一般线性群的上同调中的周期性

摘要:我们证明 $\bigoplus _{n \ge 0} \mathrm {H}^t(\mathbf {GL}_{n}(\mathbf {F}_q), \mathbf {F}_{\ell })$ 规范地承认模块在 $q$-divided power 代数上的结构(假设 $q$ 在 $\mathbf {F}_{\ell }$ 中是可逆的),因此,它是免费的和(对于 $q \neq 2$)以度 $\le t$ 生成。作为推论,我们证明有限生成的 $\mathbf {VI}$-模在非描述特征中的上同调最终在 $n$ 中是周期性的。我们应用它来获得关于单能 Specht 模块上同调的新结果。
更新日期:2021-05-07
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