Bosch–Lütkebohmert–Raynaud's conjecture on Néron models of smooth algebraic groups

Let SS be a global excellent Dedekind scheme with function field KK, and let GG be a smooth algebraic group over KK. A Néron lft-model of GG is a smooth separated SS-group algebraic space, locally of finite type, with generic fibre GG and the Néron mapping property; a Néron model is a Néron lft-model that is of finite type over SS. A subgroup is unirational if its underlying scheme admits a scheme-theoretically dominant morphism from an open subscheme of some affine space over KK. Bosch–Lütkebohmert–Raynaud's conjecture. (I) If GG contains no subgroup isomorphic to Ga\operatorname{\mathbf{G}_a}, then GG admits a Néron lft-model over SS. (II) Moreover, if GG contains no non-trivial unirational closed subgroup, then GG admits a Néron model over SS. The conjecture proposes global criteria for the existence, respectively finite-type existence, of Néron models, extending the completely understood local case. The source gives no resolution of either assertion.

Sources & referencesView supporting material

Primary source

Otto Overkamp, “On Bosch-Lütkebohmert-Raynaud's Conjecture I”, arXiv:2409.13599 (2024).

Additional references

2 papers in this index state this conjecture (2023–2024). The statement above is taken from the most recent of them; the others are arXiv:2310.14567.

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