English

On a class of semihereditary crossed-product orders

Rings and Algebras 2014-06-30 v1

Abstract

Let FF be a field, let VV be a valuation ring of FF of arbitrary Krull dimension (rank), let KK be a finite Galois extension of FF with group GG, and let SS be the integral closure of VV in KK. Let f:G×GK{0}f:G\times G\mapsto K\setminus \{0\} be a normalized two-cocycle such that f(G×G)S{0}f(G\times G)\subseteq S\setminus \{0\}, but we do not require that ff should take values in the group of multiplicative units of SS. One can construct a crossed-product VV-algebra Af=σGSxσA_f=\sum_{\sigma\in G}Sx_{\sigma} in a natural way, which is a VV-order in the crossed-product FF-algebra (K/F,G,f)(K/F,G,f). If VV is unramified and defectless in KK, we show that AfA_f is semihereditary if and only if for all σ,τG\sigma,\tau\in G and every maximal ideal MM of SS, f(σ,τ)∉M2f(\sigma,\tau)\not\in M^2. If in addition J(V)J(V) is not a principal ideal of VV, then AfA_f is semihereditary if and only if it is an Azumaya algebra over VV.

Keywords

Cite

@article{arxiv.1406.7063,
  title  = {On a class of semihereditary crossed-product orders},
  author = {John S. Kauta},
  journal= {arXiv preprint arXiv:1406.7063},
  year   = {2014}
}