Finite quotients, arithmetic invariants, and hyperbolic volume

Abstract: For any pair of orientable closed hyperbolic $3$--manifolds, this paper shows that any isomorphism between the profinite completions of their fundamental groups witnesses a bijective correspondence between the Zariski dense $\mathrm{PSL}(2,\mathbb{Q}^{\mathtt{ac}})$--representations of their fundamental groups, up to conjugacy; moreover, corresponding pairs of representations have identical invariant trace fields and isomorphic invariant quaternion algebras. (Here, $\mathbb{Q}^{\mathtt{ac}}$ denotes an algebraic closure of $\mathbb{Q}$.) Next, assuming the $p$--adic Borel regulator injectivity conjecture for number fields, this paper shows that uniform lattices in $\mathrm{PSL}(2,\mathbb{C})$ with isomorphic profinite completions have identical invariant trace fields, isomorphic invariant quaternion algebras, identical covolume, and identical arithmeticity.