English

Deformation rings which are not local complete intersections

Number Theory 2010-03-17 v1

Abstract

We study the inverse problem for the versal deformation rings R(Γ,V)R(\Gamma,V) of finite dimensional representations VV of a finite group Γ\Gamma over a field kk of positive characteristic pp. This problem is to determine which complete local commutative Noetherian rings with residue field kk can arise up to isomorphism as such R(Γ,V)R(\Gamma,V). We show that for all integers n1n \ge 1 and all complete local commutative Noetherian rings W\mathcal{W} with residue field kk, the ring W[[t]]/(pnt,t2)\mathcal{W}[[t]]/(p^n t,t^2) arises in this way. This ring is not a local complete intersection if pnW{0}p^n\mathcal{W}\neq\{0\}, so we obtain an answer to a question of M. Flach in all characteristics.

Keywords

Cite

@article{arxiv.1003.3143,
  title  = {Deformation rings which are not local complete intersections},
  author = {Frauke M. Bleher and Ted Chinburg and Bart de Smit},
  journal= {arXiv preprint arXiv:1003.3143},
  year   = {2010}
}

Comments

16 pages

R2 v1 2026-06-21T14:58:26.652Z