English

Effect of increasing the ramification on pseudo-deformation rings

Number Theory 2021-12-07 v2

Abstract

Given a continuous, odd, semi-simple 22-dimensional representation of GQ,NpG_{\mathbb{Q},Np} over a finite field of odd characteristic pp and a prime \ell not dividing NpNp, we study the relation between the universal deformation rings of the corresponding pseudo-representation for the groups GQ,NpG_{\mathbb{Q},N\ell p} and GQ,NpG_{\mathbb{Q},Np}. As a related problem, we investigate when the universal pseudo-representation arises from an actual representation over the universal deformation ring. Under some hypotheses, we prove analogues of theorems of Boston and B\"{o}ckle for the reduced pseudo-deformation rings. We improve these results when the pseudo-representation is unobstructed and pp does not divide 21\ell^2-1. When the pseudo-representation is unobstructed and pp divides +1\ell+1, we prove that the universal deformation rings in characteristic 00 and pp of the pseudo-representation for GQ,NpG_{\mathbb{Q},N\ell p} are not local complete intersection rings. As an application of our main results, we prove a big R=TR=\mathbb{T} theorem.

Keywords

Cite

@article{arxiv.1907.06608,
  title  = {Effect of increasing the ramification on pseudo-deformation rings},
  author = {Shaunak V. Deo},
  journal= {arXiv preprint arXiv:1907.06608},
  year   = {2021}
}

Comments

41 Pages, v2: following referee's comments added some remarks and a subsection in the introduction, reorganized Section 2, modified some proofs and made some minor corrections, comments are welcome