Borel complexity and automorphisms of C*-algebras

Abstract

We show that if $A$ is $\mathcal{Z}$, ${\mathcal{O}}_2$, ${\mathcal{O}}_{\infty }$, a UHF algebra of infinite type, or the tensor product of a UHF algebra of infinite type and ${\mathcal{O}}_{\infty }$, then the conjugation action $\mathrm{Aut}(A)\curvearrowright \mathrm{Aut}(A)$ is generically turbulent for the point-norm topology. We moreover prove that if $A$ is either (i) a separable C*-algebra which is stable under tensoring with $\mathcal{Z}$ or $\mathcal{K}$, or (ii) a separable ${\mathrm{II}}_1$ factor which is McDuff or a free product of ${\mathrm{II}}_1$ factors, then the approximately inner automorphisms of $A$ are not classifiable by countable structures.

19 pages