A type III$_1$ factor with the smallest outer automorphism group

Abstract

The canonical modular homomorphism provides an embedding of $\mathbb{R}$ into the outer automorphism group Out($M$) of any type III$_{1}$ factor $M$. We provide an explicit construction of a full factor of type III$_{1}$ with separable predual such that the outer automorphism group is minimal, i.e. this embedding is an isomorphism. We obtain such a III$_{1}$ factor by using an amalgamated free product construction.