2024/10/30 by Burton, Peter, Panangaden, Jane
#30E20 #37A44 #37A55 #46L55 #Complex Variables (math.CV) #Dynamical Systems (math.DS) #FOS: Mathematics #Operator Algebras (math.OA)
paper · doi:10.48550/arxiv.2410.22701
Furstenberg's × 2 × 3 conjecture has remained a central open problem in ergodic theory for over 50 years, and it serves as the basic test case for a broad class of rigidity phenomena which are believed to hold in number-theoretic dynamics. More recently, two related statements have appeared in the literature: a question about periodic approximation raised by Levit and Vigdorovich in the context of approximate group theory and a periodic equidistribution conjecture formulated by Lindenstrauss. The purpose of this article is to provide equivalent formulations for these three statements in a complex-analytic setting and an operator-algebraic setting, giving nine conjectures grouped into three triples. The complex-analytic conjectures involve so-called Carathéodory functions on the unit disk that satisfy a certain functional identity, and we find that Furstenberg's conjecture is equivalent to the assertion that every such function is a convex combination of rational functions. The operator-algebraic conjectures involve tracial states on the full group C^∗-algebra of a certain semidirect product, which is related to Baumslag-Solitar groups.