学术文献库

In this second article, we continue to study classes of groups constructed from a functorial method due to Vaughan Jones. A key observation of the author shows that these groups have remarkable diagrammatic properties that can be used to deduce their properties. Given any group and two of its endomorphisms, we construct a semidirect product. In our first article dedicated to this construction, we classify up to isomorphism all these semidirect products when one of the endomorphisms is trivial and described their automorphism group. In this article we focus on the case where both endomorphisms are automorphisms. The situation is rather different and we obtain semidirect products where the largest Richard Thompson's group $V$ is acting on some discrete analogues of loop groups. Note that these semidirect products appear naturally in recent constructions of quantum field theories. Moreover, they have been previously studied by Tanushevski and can be constructed via the framework of cloning systems of Witzel-Zaremsky. In particular, they provide examples of groups with various finiteness properties and possible counterexamples of a conjecture of Lehnert on co-context-free groups. We provide a partial classification of these semidirect products and describe explicitly their automorphism group. Moreover, we prove that groups studied in the first and second articles are never isomorphic to each other nor admit nice embeddings between them. We end the article with an appendix comparing Jones technology with Witzel-Zaremsky's cloning systems and with Tanushevski's construction. As in the first article, all the results presented were possible to achieve via a surprising rigidity phenomena on isomorphisms between these groups.