Algebraic commutators with respect to subnormal subgroups in division rings

Abstract

Let $D$ be a division ring and $K$ a subfield of $D$ which is not necessarily contained in the center $F$ of $D$. In this paper, we study the structure of $D$ under the condition of left algebraicity of certain subsets of $D$ over $K$. Among results, it is proved that if $D^{\ast }$ contains a noncentral normal subgroup which is left algebraic over $K$ of bounded degree $d$, then $[D:F]\le d^2$. In case $K=F$, the obtained results show that if either all additive commutators or all multiplicative commutators with respect to a noncentral subnormal subgroup of $D^{\ast }$ are algebraic of bounded degree $d$ over $F$, then $[D:F]\le d^2$.

15 pages, accepted for publication in Acta Mathematica Hungarica