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arXiv 2203.07974math.RTmath.NTmath.OA
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约化Adelic群的Plancherel测度与Von Neumann维数

Plancherel Measures of Reductive Adelic Groups and Von Neumann Dimensions

Jun Yang

摘要:

给定数域$F$和$F$上的约化群$G$,由其局部群$G(F_v)$的Plancherel测度可以确定椭圆群$G(\mathbb{A}_F)$及其上的Placerel测度$ν_{G(\mathbb{A}_F)}$的酉对偶$\hat{G(\mathbb{A}_F)}$.给定有限Plancherel测度的子集$X\subset \hat{G(\mathbb{A}_F)}$,设$H_X$是$X$中不可约表示的直积分.除了一个$G(\mathbb{A}_F)$ -模和一个$G(F)$ -模之外,$H_X$也是群冯诺依曼代数$\mathcal{L}(G(F))$上的一个模,因此存在一个标准维数$\dim_{\mathcal{L}(G(F))}H_X\in [0,\infty)$ .证明了如果$G$是半单单连通的,且$G(\mathbb{A}_F)$具有Tamagawa测度,则$G(\mathbb{A}_F)$的Plancherel测度与代数$\mathcal{L}(G(F))$:$\dim_{\mathcal{L}(G(F))}H_X=ν_{G(\mathbb{A}_F)}(X)$上的维数一致.

英文摘要:

Given a number field $F$ and a reductive group $G$ over $F$, the unitary dual $\hat{G(\mathbb{A}_F)}$ of the adelic group $G(\mathbb{A}_F)$ and the Placherel measure $ν_{G(\mathbb{A}_F)}$ on it can be determined by the Plancherel measure of its local groups $G(F_v)$. Given a subset $X\subset \hat{G(\mathbb{A}_F)}$ of finite Plancherel measure, let $H_X$ be the direct integral of the irreducible representations in $X$. Besides a $G(\mathbb{A}_F)$-module and a $G(F)$-module, $H_X$ is also a module over the group von Neumann algebra $\mathcal{L}(G(F))$, hence there is a canonical dimension $\dim_{\mathcal{L}(G(F))}H_X\in [0,\infty)$. It is proved that the Plancherel measure of $G(\mathbb{A}_F)$ coincides with the dimension over the algebra $\mathcal{L}(G(F))$: $\dim_{\mathcal{L}(G(F))}H_X=ν_{G(\mathbb{A}_F)}(X)$, if $G$ is semisimple, simply connected and $G(\mathbb{A}_F)$ is equipped with the Tamagawa measure.

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