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Inverse problems for deformation rings
Journal article   Open access   Peer reviewed

Inverse problems for deformation rings

Frauke M. Bleher, Ted Chinburg and Bart de Smit
Transactions of the American Mathematical Society, Vol.365(11), pp.6149-6165
11/01/2013
DOI: 10.1090/S0002-9947-2013-05848-5
url
https://doi.org/10.1090/S0002-9947-2013-05848-5View
Published (Version of record) Open Access

Abstract

Let W be a complete Noetherian local commutative ring with residue field k of positive characteristic p. We study the inverse problem for the universal deformation rings RW(Γ, V) relative to W of finite dimensional representations V of a profinite group Γ over k. We show that for all p and n ≥ 1, the ring W[[t]]/(pnt, t2) arises as a universal deformation ring. This ring is not a complete intersection if pnW ≠ {0}, so we obtain an answer to a question of M. Flach in all characteristics. We also study the 'inverse inverse problem' for the ring W[[t]]/(pnt, t2); this is to determine all pairs (Γ, V) such that RW(Γ, V) is isomorphic to this ring.
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