Noncommutative Brownian motions with Kesten distributions and related Poisson processes

TL;DR

This paper introduces a two-parameter family of noncommutative Brownian motions that interpolate between free and monotone probability, using ordered non-crossing partitions and related combinatorics.

Contribution

It presents a novel interpolation framework connecting free and monotone probability through noncommutative Brownian motions and Poisson processes, based on new combinatorial structures.

Findings

Provides a new interpolation between free and monotone Brownian motions.

Establishes relations between Delaney's and Euler's numbers via non-crossing partitions.

Demonstrates that mixed moments reproduce free and monotone counterparts.

Abstract

We introduce and study a noncommutative two-parameter family of noncommutative Brownian motions in the free Fock space. They are associated with Kesten laws and give a continuous interpolation between Brownian motions in free probability and monotone probability. The combinatorics of our model is based on ordered non-crossing partitions, in which to each such partition $P$ we assign a weight depending on the numbers of disorders and orders in $P$ related to the natural partial order on the set of blocks of $P$ implemented by the relation of being inner or outer. In particular, we obtain a simple relation between Delaney's numbers (related to inner blocks in non-crossing partitions) and generalized Euler's numbers (related to orders and disorders in ordered non-crossing partitions). An important feature of our interpolation is that the mixed moments of the corresponding creation and annihilation processes also reproduce their monotone and free counterparts, which does not take place in other interpolations. The same combinatorics is used to construct an interpolation between free and monotone Poisson processes.