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Sur le groupe unitaire relatif à une involution d’un corps algébriquement clos

Bruno Deschamps (2011)

Journal de Théorie des Nombres de Bordeaux

Dans cet article, nous tentons de généraliser à d’autres situations l’isomorphisme de groupes topologiques qui existe entre le groupe / et le groupe unitaire 𝕌 = { z / | z | = 1 } .Nous montrons que cet isomorphisme existe algébriquement en toute généralité : pour tout corps algébriquement clos C et toute involution c de C les groupes 𝕌 ( C , c ) = { z C / z c ( z ) = 1 } et C < c > / sont isomorphes. Nous donnons ensuite un exemple d’involution c 0 de qui n’est pas conjuguée, dans le groupe Aut ( ) , à la conjugaison complexe et telle que 𝕌 ( , c 0 ) soit topologiquement isomorphe...

The arithmetic of curves defined by iteration

Wade Hindes (2015)

Acta Arithmetica

We show how the size of the Galois groups of iterates of a quadratic polynomial f can be parametrized by certain rational points on the curves Cₙ: y² = fⁿ(x) and their quadratic twists (here fⁿ denotes the nth iterate of f). To that end, we study the arithmetic of such curves over global and finite fields, translating key problems in the arithmetic of polynomial iteration into a geometric framework. This point of view has several dynamical applications. For instance, we establish a maximality theorem...

The local lifting problem for actions of finite groups on curves

Ted Chinburg, Robert Guralnick, David Harbater (2011)

Annales scientifiques de l'École Normale Supérieure

Let k be an algebraically closed field of characteristic p > 0 . We study obstructions to lifting to characteristic 0 the faithful continuous action φ of a finite group G on k [ [ t ] ] . To each such  φ a theorem of Katz and Gabber associates an action of G on a smooth projective curve Y over k . We say that the KGB obstruction of φ vanishes if G acts on a smooth projective curve X in characteristic  0 in such a way that X / H and Y / H have the same genus for all subgroups H G . We determine for which G the KGB obstruction...

The Sylow p-Subgroups of Tame Kernels in Dihedral Extensions of Number Fields

Qianqian Cui, Haiyan Zhou (2013)

Bulletin of the Polish Academy of Sciences. Mathematics

Let F/E be a Galois extension of number fields with Galois group D 2 . In this paper, we give some expressions for the order of the Sylow p-subgroups of tame kernels of F and some of its subfields containing E, where p is an odd prime. As applications, we give some results about the order of the Sylow p-subgroups when F/E is a Galois extension of number fields with Galois group D 16 .

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