778 articles – 1385 references  [version française]
 HAL: hal-00204107, version 1
 arXiv: 0801.1942
 Available versions: v1 (2008-01-13) v2 (2008-01-24)
 On smooth curves endowed with a large automorphism $p$-group in characteristic $p>0$.
 (2008-01-12)
 Let $k$ be an algebraically closed field of characteristic $p>0$ and $C$ a connected nonsingular projective curve over $k$ with genus $g \geq 2$. This paper continues the work begun by Lehr and Matignon, namely the study of "big actions", i.e. the pairs $(C,G)$ where $G$ is a $p$-subgroup of the $k$-automorphism group of $C$ such that $\frac{|G|}{g} >\frac{2\,p}{p-1}$. If $G_2$ denotes the second ramification group of $G$ at the unique ramification point of the cover $C \rightarrow C/G$, we first display necessary conditions on $G_2$ for $(C,G)$ to be a big action, which allows us to pursue the classification of big actions. Our main source of examples comes from the construction of curves with many rational points using ray class field theory for global function fields, as initiated by J-P. Serre and followed by Lauter and Auer. In particular, we obtain explicit examples of big actions with $G_2$ abelian of large exponent.
 1: Institut de Mathématiques de Bordeaux (IMB) CNRS : UMR5251 – Université Sciences et Technologies - Bordeaux I – Université Victor Segalen - Bordeaux II
 Subject : Mathematics/Number TheoryMathematics/Algebraic Geometry
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 hal-00204107, version 1 http://hal.archives-ouvertes.fr/hal-00204107 oai:hal.archives-ouvertes.fr:hal-00204107 From: Magali Rocher <> Submitted on: Saturday, 12 January 2008 10:17:57 Updated on: Sunday, 13 January 2008 10:37:54