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pro vyhledávání: '"Overkamp, Otto"'
Autor:
Overkamp, Otto
Let $G$ be a smooth algebraic group over the field of rational functions of an excellent Dedekind scheme $S$ of equal characteristic $p>0.$ A N\'eron lft-model of $G$ is a smooth separated model $\mathscr{G} \to S$ of $G$ satisfying a universal prope
Externí odkaz:
http://arxiv.org/abs/2409.13599
Autor:
Overkamp, Otto, Suzuki, Takashi
We first prove Bosch-L\"utkebohmert-Raynaud's conjectures on existence of global N\'eron models of not necessarily semi-abelian algebraic groups in the perfect residue fields case. We then give a counterexample to the existence in the imperfect resid
Externí odkaz:
http://arxiv.org/abs/2310.14567
Autor:
Overkamp, Otto, Suzuki, Takashi
The base change conductor is an invariant introduced by Chai which measures the failure of a semiabelian variety to have semiabelian reduction. We investigate the behaviour of this invariant in short exact sequences, as well as under duality and isog
Externí odkaz:
http://arxiv.org/abs/2310.01289
Autor:
Overkamp, Otto
We prove Chai's conjecture on the additivity of the base change conductor of semiabelian varieties in the case of Jacobians of proper curves. This includes the first infinite family of non-trivial wildly ramified examples. Along the way, we extend Ra
Externí odkaz:
http://arxiv.org/abs/2212.05018
Autor:
Overkamp, Otto, Smeets, Arne
We give cohomological criteria for logarithmic good reduction of elliptic surfaces up to modification. Along the way, we prove several more general results about such surfaces in positive characteristic, as well as about log smooth morphisms.
Externí odkaz:
http://arxiv.org/abs/2212.01070
Autor:
Overkamp, Otto
We study the structure of Jacobians of geometrically reduced curves over arbitrary (i. e., not necessarily perfect) fields. We show that, while such a group scheme cannot in general be decomposed into an affine and an Abelian part as over perfect fie
Externí odkaz:
http://arxiv.org/abs/2110.00545
Autor:
Overkamp, Otto
We study N\'eron models of pseudo-Abelian varieties over excellent discrete valuation rings of equal characteristic $p>0$ and generalize the notions of good reduction and semiabelian reduction to such algebraic groups. We prove that the well-known re
Externí odkaz:
http://arxiv.org/abs/2003.03764
Akademický článek
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Autor:
Overkamp, Otto
Publikováno v:
Math. Proc. Camb. Phil. Soc. 171 (2021) 65-97
We prove that a Kummer surface defined over a complete strictly Henselian discretely valued field $K$ of residue characteristic different from 2 admits a strict Kulikov model after finite base change. The Kulikov models we construct will be schemes,
Externí odkaz:
http://arxiv.org/abs/1806.10105
Autor:
Overkamp, Otto
We investigate N\'eron models of Jacobians of singular curves over strictly Henselian discretely valued fields, and their behaviour under tame base change. For a semiabelian variety, this behaviour is governed by a finite sequence of (a priori) real
Externí odkaz:
http://arxiv.org/abs/1710.06663