## Abstract

Let F be a field of odd prime characteristic p, G a group, U the group of units in the group algebra FG, and U ^{+} the subgroup of U generated by the elements of U fixed by the anti-automorphism of FG which inverts all elements of G. It is known that U is nilpotent if G is nilpotent and the commutator subgroup G′ has p-power order, and then the nilpotency class of U is at most the order of G′; this bound is attained if and only if G′ is cyclic and not a Sylow subgroup of G. Adalbert Bovdi and János Kurdics proved the 'if' part of this last statement by exhibiting a nontrivial commutator of the relevant weight. For the special case when G is a nonabelian torsion group (so G′ cannot possibly be a Sylow subgroup), the present paper identifies such a commutator in U ^{+}, showing (Theorem 1) that the same bound is attained even by the nilpotency class of this subgroup. We do not know what happens when G′ is not a Sylow subgroup but G is not torsion. It can happen that U ^{+} is nilpotent even though U is not. The torsion groups G which allow this are known (from the work of Gregory T. Lee) to be precisely the direct products of a finite p-group P, a quaternion group Q of order 8, and an elementary abelian 2-group. Theorem 2: in this case, the nilpotency class of U ^{+} is strictly smaller than the nilpotency index of the augmentation ideal of the group algebra FP, and this bound is attained whenever P is a powerful p-group. The nonabelian group P of order 27 and exponent 3 is not powerful, yet the G = P × Q formed with this P also leads to a U ^{+} attaining the general bound, so here a necessary and sufficient condition remains elusive.

Original language | English |
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Pages (from-to) | 171-180 |

Number of pages | 10 |

Journal | Publicationes Mathematicae |

Volume | 79 |

Issue number | 1-2 |

DOIs | |

Publication status | Published - 2011 |

Externally published | Yes |

## Keywords

- Group ring
- Involution
- Nilpotency class
- Symmetric units

## ASJC Scopus subject areas

- Mathematics(all)