English

On Clifford theory with Galois action

Group Theory 2016-04-26 v3 Representation Theory

Abstract

Let G^\widehat{G} be a finite group, NN a normal subgroup of G^\widehat{G} and θIrrN\theta\in \operatorname{Irr}N. Let F\mathbb{F} be a subfield of the complex numbers and assume that the Galois orbit of θ\theta over F\mathbb{F} is invariant in G^\widehat{G}. We show that there is another triple (G^1,N1,θ1)(\widehat{G}_1,N_1,\theta_1) of the same form, such that the character theories of G^\widehat{G} over θ\theta and of G^1\widehat{G}_1 over θ1\theta_1 are essentially "the same" over the field F\mathbb{F} and such that the following holds: G^1\widehat{G}_1 has a cyclic normal subgroup CC contained in N1N_1, such that θ1=λN1\theta_1=\lambda^{N_1} for some linear character λ\lambda of CC, and such that N1/CN_1/C is isomorphic to the (abelian) Galois group of the field extension F(λ)/F(θ1)\mathbb{F}(\lambda)/\mathbb{F}(\theta_1). More precisely, "the same" means that both triples yield the same element of the Brauer-Clifford group BrCliff(G,F(θ))\operatorname{BrCliff}(G,\mathbb{F}(\theta)) defined by A. Turull.

Keywords

Cite

@article{arxiv.1409.3559,
  title  = {On Clifford theory with Galois action},
  author = {Frieder Ladisch},
  journal= {arXiv preprint arXiv:1409.3559},
  year   = {2016}
}

Comments

v3: Referee's comments included, and a few other small corrections