English

Noether's normalization in skew polynomial rings

Rings and Algebras 2025-07-02 v2

Abstract

We study Noether's normalization lemma for finitely generated algebras over a division algebra. In its classical form, the lemma states that if II is a proper ideal of the ring R=F[t1,,tn]R=F[t_1,\ldots,t_n] of polynomials over a field FF, then the quotient ring R/IR/I is a finite extension of a polynomial ring over FF. We prove that the lemma holds when R=D[t1,,tn]R=D[t_1,\ldots,t_n] is the ring of polynomials in nn central variables over a division algebra DD. We provide examples demonstrating that Noether's normalization may fail for the skew polynomial ring D[t1,,tn;σ1,,σn]D[t_1,\ldots,t_n;\sigma_1,\ldots,\sigma_n] with respect to commuting automorphisms σ1,,σn\sigma_1,\ldots,\sigma_n of DD. We give a sufficient condition for σ1,,σn\sigma_1,\ldots,\sigma_n under which the normalization lemma holds for such ring. In the case where D=FD=F is a field, this sufficient condition is proved to be necessary.

Keywords

Cite

@article{arxiv.2407.12686,
  title  = {Noether's normalization in skew polynomial rings},
  author = {Elad Paran and Thieu N. Vo},
  journal= {arXiv preprint arXiv:2407.12686},
  year   = {2025}
}
R2 v1 2026-06-28T17:44:39.079Z