Algebraic Groups Constructed From Rings with Involution

Abstract

We define a class of groups constructed from rings equipped with an involution. We show that under suitable conditions, these groups are either algebraic or arithmetic, including as special cases the orientation-preserving isometry group of hyperbolic 4-space, $SL(2,R)$ for any commutative ring $R$, various symplectic and orthogonal groups, and an important class of arithmetic subgroups of $S{O}^{+}(4,1)$. We investigate when such groups are isomorphic and conjugate, and relate this to problem of determining when hyperbolic $4$-orbifolds are homotopic.

This is essentially a re-draft of arXiv:1908.01250. However, as there have been significant changes (including the title), it made sense to resubmit as a separate document