Operators related to subordination for free multiplicative convolutions

Abstract

It has been shown by Voiculescu and Biane that the analytic subordina- tion property holds for free additive and multiplicative convolutions. In this paper, we present an operatorial approach to subordination for free multiplicative convolutions. This study is based on the concepts of 'freeness with subordination', or 's-free inde- pendence', and 'orthogonal independence', introduced recently in the context of free additive convolutions. In particular, we introduce and study the associated multiplica- tive convolutions and construct related operators, called 'subordination operators' and 'subordination branches'. Using orthogonal independence, we derive decompositions of subordination branches and related decompositions of s-free and free multiplicative convolutions. The operatorial methods lead to several new types of graph products, called 'loop products', associated with different notions of independence (monotone, boolean, orthogonal, s-free). We also prove that the enumeration of rooted 'alternat- ing double return walks' on the loop products of graphs and on the free product of graphs gives the moments of the corresponding multiplicative convolutions.