A construction which relates c-freeness to infinitesimal freeness

Abstract

We consider two extensions of free probability that have been studied in the research literature, and are based on the notions of <i>c-freeness</i> and respectively of <i>infinitesimal freeness</i> for noncommutative random variables. In a 2012 paper, Belinschi and Shlyakhtenko pointed out a connection between these two frameworks, at the level of their operations of 1-dimensional free additive convolution. Motivated by that, we propose a construction which produces a multi-variate version of the Belinschi-Shlyakhtenko result, together with a result concerning free products of multi-variate noncommutative distributions. Our arguments are based on the combinatorics of the specific types of cumulants used in c-free and in infinitesimal free probability. They work in a rather general setting, where the initial data consists of a vector space V given together with a linear map Δ : V → V ⊗ V. In this setting, all the needed brands of cumulants live in the guise of families of multilinear functionals on V, and our main result concerns a certain transformation Δ^* on such families of multilinear functionals.