The Base Change Of Fundamental Group Schemes

Fuente: arXiv
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Auteurs principaux: Li, Lingguang, Tian, Niantao
Format: Preprint
Publié: 2026
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author Li, Lingguang
Tian, Niantao
author_facet Li, Lingguang
Tian, Niantao
contents Let $k$ be a field, $K/k$ a field extension, $X$ a connected scheme proper over $k$, $x_K\in X_K(K)$ lying over $x\in X(k)$, $\mathcal{C}_X$ and $\mathcal{C}_{X_K}$ the Tannakian categories over $X$ and $X_K$ respectively, $π(\mathcal{C}_X,x)$ and $π(\mathcal{C}_{X_K},x_K)$ the corresponding Tannaka group schemes respectively. We give equivalent conditions to the isomorphisms of fundamental group schemes $$π(\mathcal{C}_{X_K},x_K)\xrightarrow{\cong} π(\mathcal{C}_X,x)_K.$$ As application, we generalize the base change of certain fundamental group schemes under separable extension and extension of algebraically closed fields, such as S, Nori, EN, F, Étale, Loc, ELoc and Unipotent fundamental group schemes.
format Preprint
id arxiv_https___arxiv_org_abs_2602_11110
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle The Base Change Of Fundamental Group Schemes
Li, Lingguang
Tian, Niantao
Algebraic Geometry
14F35, 14L15, 14J60
Let $k$ be a field, $K/k$ a field extension, $X$ a connected scheme proper over $k$, $x_K\in X_K(K)$ lying over $x\in X(k)$, $\mathcal{C}_X$ and $\mathcal{C}_{X_K}$ the Tannakian categories over $X$ and $X_K$ respectively, $π(\mathcal{C}_X,x)$ and $π(\mathcal{C}_{X_K},x_K)$ the corresponding Tannaka group schemes respectively. We give equivalent conditions to the isomorphisms of fundamental group schemes $$π(\mathcal{C}_{X_K},x_K)\xrightarrow{\cong} π(\mathcal{C}_X,x)_K.$$ As application, we generalize the base change of certain fundamental group schemes under separable extension and extension of algebraically closed fields, such as S, Nori, EN, F, Étale, Loc, ELoc and Unipotent fundamental group schemes.
title The Base Change Of Fundamental Group Schemes
topic Algebraic Geometry
14F35, 14L15, 14J60
url https://arxiv.org/abs/2602.11110