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arXiv 0807.2286math.AGmath.NT
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一个相对方案的基本群方案与其类属光纤的比较

Comparison between the fundamental group scheme of a relative scheme and that of its generic fiber

Marco Antei

摘要:

证明了连通Dedekind概型上$X$的类纤$X_η$的基本群概型与$X$的基本群概型的类纤之间的自然态射$ϕ:π_1(X_η,x_η)\to π_1(X,x)_η$总是忠实平坦的.作为应用,我们给出了$X_η$上的有限控制点$G$ -扭子在$X$上扩张的一个充要条件.我们最后提供了$ϕ:π_1(X_η,x_η)\to π_1(X,x)_η$是同构的例子。

英文摘要:

We show that the natural morphism $ϕ:π_1(X_η,x_η)\to π_1(X,x)_η$ between the fundamental group scheme of the generic fiber $X_η$ of a scheme $X$ over a connected Dedekind scheme and the generic fiber of the fundamental group scheme of $X$ is always faithfully flat. As an application we give a necessary and sufficient condition for a finite, dominated pointed $G$-torsor over $X_η$ to be extended over $X$. We finally provide examples where $ϕ:π_1(X_η,x_η)\to π_1(X,x)_η$ is an isomorphism..

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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