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Explicit Selmer groups for cyclic covers of ℙ¹

Michael Stoll, Ronald van Luijk (2013)

Acta Arithmetica

For any abelian variety J over a global field k and an isogeny ϕ: J → J, the Selmer group S e l ϕ ( J , k ) is a subgroup of the Galois cohomology group H ¹ ( G a l ( k s / k ) , J [ ϕ ] ) , defined in terms of local data. When J is the Jacobian of a cyclic cover of ℙ¹ of prime degree p, the Selmer group has a quotient by a subgroup of order at most p that is isomorphic to the ‘fake Selmer group’, whose definition is more amenable to explicit computations. In this paper we define in the same setting the ‘explicit Selmer group’, which is isomorphic...

Extension of Estermann’s theorem to Euler products associated to a multivariate polynomial

Ludovic Delabarre (2013)

Bulletin de la Société Mathématique de France

Given a multivariate polynomial h X 1 , , X n with integral coefficients verifying an hypothesis of analytic regularity (and satisfying h ( 0 ) = 1 ), we determine the maximal domain of meromorphy of the Euler product p prime h p - s 1 , , p - s n and the natural boundary is precisely described when it exists. In this way we extend a well known result for one variable polynomials due to Estermann from 1928. As an application, we calculate the natural boundary of the multivariate Euler products associated to a family of toric varieties.

Failure of the Hasse principle for Châtelet surfaces in characteristic 2

Bianca Viray (2012)

Journal de Théorie des Nombres de Bordeaux

Given any global field k of characteristic 2 , we construct a Châtelet surface over k that fails to satisfy the Hasse principle. This failure is due to a Brauer-Manin obstruction. This construction extends a result of Poonen to characteristic 2 , thereby showing that the étale-Brauer obstruction is insufficient to explain all failures of the Hasse principle over a global field of any characteristic.

Families of hypersurfaces of large degree

Christophe Mourougane (2012)

Journal of the European Mathematical Society

Grauert and Manin showed that a non-isotrivial family of compact complex hyperbolic curves has finitely many sections. We consider a generic moving enough family of high enough degree hypersurfaces in a complex projective space. We show the existence of a strict closed subset of its total space that contains the image of all its sections.

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