Essentially finite $G$-torsors
| Autor: | Ghiasabadi, Archia, Reppen, Stefan |
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| Rok vydání: | 2022 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | Let $X$ be a smooth projective curve of genus $g$, defined over an algebraically closed field $k$, and let $G$ be a connected reductive group over $k$. We say that a $G$-torsor is essentially finite if it admits a reduction to a finite group, generalising the notion of essentially finite vector bundles to arbitrary groups $G$. We give a Tannakian interpretation of such torsors, and we prove that all essentially finite $G$-torsors have torsion degree, and that the degree is 0 if $X$ is an elliptic curve. We then study the density of the set of $k$-points of essentially finite $G$-torsors of degree $0$, denoted $M_{G}^{\text{ef},0}$, inside $M_{G}^{\text{ss},0}$, the $k$-points of all semistable degree 0 $G$-torsors. We show that when $g=1$, $M_{G}^{\text{ef}}\subset M_{G}^{\text{ss},0}$ is dense. When $g>1$ and when $\text{char}(k)=0$, we show that for any reductive group of semisimple rank 1, $M_{G}^{\text{ef},0}\subset M_{G}^{\text{ss},0}$ is not dense. Comment: Final version. To appear in Bull. Sci. math |
| Databáze: | arXiv |
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