Subnormal subgroups and self-invariant maximal subfields in division rings

Abstract

A maximal subfield of a division ring is said to be self-invariant if it is its own normalizer. Subfields of this kind are important because they have a strong connection with Albert's conjecture on the cyclicity of division rings of prime index. We show that every maximal subfield of the Mal'cev-Neumann division ring, which is of infinite dimension, is self-invariant. We also apply the Mal'cev-Neumann structure to refute the conjecture that every noncentral subnormal subgroup of the multiplicative group of a division ring must contain a noncentral normal subgroup. Finally, among other things, we rely on self-invariant subfields to present a criterion for a division ring to have a finite-dimensional subdivision rings.