More on constructing counterexamples
to
Burnside and Kurosh problems
by
Lakhdar Hammoudi
Abstract: About a century ago Burnside raised
the idea of finiteness in group theory by asking whether a finitely generated
(f.g.) periodic group is necessarily finite. This question gave birth
to the study of finiteness conditions in algebra and led to the proliferation
of Burnside type problems. Probably the most striking among these problems
is the 1941 question of Kurosh about the existence of a f.g. infinite dimensional
algebraic algebra. This problem is in fact strongly related to that
of Burnside. Actually, in 1945 Jacobson observed that a counterexample to
the Kurosh problem gives a counterexample to the Burnside problem.
However, Kurosh's question is also connected to other difficult questions
such as the Koethe and Amitsur conjectures. Although there are many
counterexamples to the Burnside problem, for a long time, however the only
known counterexamples to both the Burnside and Kurosh problems were those
constructed by Golod, using the well known Golod-Shafarevich lemma.
Recently Smoktunowicz constructed a 3 generated nil algebra over a denumerable
field such that its algebra of polynomials with two commuting indeterminates
is not nil. These algebras cannot be constructed over a nondenumerable
field, since every f.g. nil algebra over a nondenumerable field is absolutely
nil. Our main goal here is to develop a technique to give new counterexamples
to the Burnside and Kurosh problems. We mainly show that for any integer
$d\geq 2$ and over any field ${\mathbb {K}}$, we construct a residually finite
non nilpotent nil algebra over ${\mathbb {K}}$ generated by $d$ elements
such that any $d-1$ elements generate a nilpotent subalgebra. This
leads to analogous results for nonassociative algebras and groups.
We shall point out that we made the effort to prove that our technique gives
similar results to Golod's. On the other hand, although our algebras
and groups satisfy the Golod-Shafarevich lemma, the proof is completely different,
as we do not use this lemma. Our algebras are also different from Smoktunowicz's
as we carry out our construction over every field, which leads to absolutely
nil algebras.