Free positive multiplicative Brownian motion and the free additive convolution of semicircle and uniform distribution

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Main Author: Auer, Martin
Format: Preprint
Published: 2025
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author Auer, Martin
author_facet Auer, Martin
contents The free positive multiplicative Brownian motion $(h_t)_{t\geq0}$ is the large $N$ limit in non-commutative distribution of matrix geometric Brownian motion. It can be constructed by setting $h_t:=g_{t/2}g_{t/2}^*$, where $(g_t)_{t\geq0}$ is a free multiplicative Brownian motion, which is the large $N$ limit in non-commutative distribution of the Brownian motion in $\operatorname{Gl}(N,\mathbb{C})$. One key property of $(h_t)_{t\geq0}$ is the fact that the corresponding spectral distributions $(ν_t)_{t\geq0}\subset M^1((0,\infty))$ form a semigroup w.r.t. free multiplicative convolution. In recent work by M. Voit and the present author, it was shown that $ν_t$ can be expressed by the image measure of a free additive convolution of the semicircle and the uniform distribution on an interval under the exponential map. In this paper, we provide a new proof of this result by calculating the moments of the free additive convolution of semicircle and uniform distributions on intervals. As a by-product, we also obtain new integral formulas for $ν_t$ which generalize the corresponding known moment formulas involving Laguerre polynomials.
format Preprint
id arxiv_https___arxiv_org_abs_2505_05984
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Free positive multiplicative Brownian motion and the free additive convolution of semicircle and uniform distribution
Auer, Martin
Probability
Combinatorics
Functional Analysis
Operator Algebras
Primary 46L54, Secondary 60B20, 60E10, 05A19, 33C15
The free positive multiplicative Brownian motion $(h_t)_{t\geq0}$ is the large $N$ limit in non-commutative distribution of matrix geometric Brownian motion. It can be constructed by setting $h_t:=g_{t/2}g_{t/2}^*$, where $(g_t)_{t\geq0}$ is a free multiplicative Brownian motion, which is the large $N$ limit in non-commutative distribution of the Brownian motion in $\operatorname{Gl}(N,\mathbb{C})$. One key property of $(h_t)_{t\geq0}$ is the fact that the corresponding spectral distributions $(ν_t)_{t\geq0}\subset M^1((0,\infty))$ form a semigroup w.r.t. free multiplicative convolution. In recent work by M. Voit and the present author, it was shown that $ν_t$ can be expressed by the image measure of a free additive convolution of the semicircle and the uniform distribution on an interval under the exponential map. In this paper, we provide a new proof of this result by calculating the moments of the free additive convolution of semicircle and uniform distributions on intervals. As a by-product, we also obtain new integral formulas for $ν_t$ which generalize the corresponding known moment formulas involving Laguerre polynomials.
title Free positive multiplicative Brownian motion and the free additive convolution of semicircle and uniform distribution
topic Probability
Combinatorics
Functional Analysis
Operator Algebras
Primary 46L54, Secondary 60B20, 60E10, 05A19, 33C15
url https://arxiv.org/abs/2505.05984