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arXiv 2603.05554math.AGmath.NT
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抛物群方案的简化

Reductification of parahoric group schemes

Arnab Kundu

AI总结:

本文研究抛物群方案在有限伽罗华扩张下的可约性,并证明在良好余特征下,一般平凡抛物 torsors 的平凡性。

摘要:

抛物群方案是某些可能非可约、光滑、有理积分模型的可约群方案,在一个赫森利安离散赋值域K上定义,其余赋值域是完美域。我们证明,任何这样的群方案P在某个(可能剧烈分歧的)有限伽罗华扩张L/K后成为可约的。更具体地说,我们证明存在一个可约的积分模型G,使得P可以恢复为G的韦尔限制的伽罗华不变子群的平滑。我们的工作扩展了Balaji-Seshadri和Pappas-Rapoport在温和分歧和单连通半单设定下的结果。作为应用,我们建立了抛物群的格罗滕迪克-塞雷猜想的抛物类比,在足够好的余特征情况下。具体来说,我们确认当通用可约群是单连通时,一般平凡的抛物 torsors 是平凡的。证明通过将问题归结为一个堆叠可约群在堆叠离散赋值环上的陈述。

英文摘要:

Parahoric group schemes are certain possibly non-reductive, smooth, affine integral models of reductive group schemes defined over a henselian discretely valued field $K$ whose residue field is perfect. We show that any such group scheme $\mathscr{P}$ becomes reductive, in a particular regard, after a (possibly wildly ramified) finite Galois extension $L/K$. More precisely, we prove that there exists a reductive integral model $\mathscr{G}$ of the base change $\mathscr{P}_L$ such that $\mathscr{P}$ can be recovered as the smoothening of the subgroup of Galois invariants of the Weil restriction of $\mathscr{G}$. Our work extends results of Balaji--Seshadri and Pappas--Rapoport from the tamely ramified and simply-connected semisimple setting. As an application, we establish a parahoric analogue of the Grothendieck--Serre conjecture in sufficiently good residue characteristics. Specifically, we confirm that generically trivial parahoric torsors are trivial whenever the generic reductive group is simply-connected. The proof proceeds by reducing the problem to a statement about a stacky reductive group over a stacky discrete valuation ring.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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