On finite extensions of lamplighter groups

Abstract

We study a family of groups consisting of the simplest extensions of lamplighter groups. We use these groups to answer multiple open questions in combinatorial group theory, providing groups that exhibit various combinations of properties: 1) Decidable Subgroup Membership and undecidable Uniform Subgroup Membership Problem, 2) Rational volume growth series and undecidable Word Problem and 3) Recursive (even context-free) language of conjugacy geodesics, decidable Word Problem, and undecidable Conjugacy Problem. We also consider the co-Word Problem, residual finiteness and the Isomorphism Problem within this class.

27 pages, 6 figures. v2: Removed the very last (wrong) remark, and fixed a reference