The Brown measure of the sum of a self-adjoint element and an imaginary multiple of a semicircular element

Jun 12, 2020
50 pages
Published in:
  • Lett.Math.Phys. 112 (2022) 2, 19
  • Published: Mar 7, 2022
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Abstract: (Springer)
We compute the Brown measure of x0+iσtx_{0}+i\sigma _{t}, where σt\sigma _{t} is a free semicircular Brownian motion and x0x_{0} is a freely independent self-adjoint element that is not a multiple of the identity. The Brown measure is supported in the closure of a certain bounded region Ωt\Omega _{t} in the plane. In Ωt,\Omega _{t}, the Brown measure is absolutely continuous with respect to Lebesgue measure, with a density that is constant in the vertical direction. Our results refine and rigorize results of Janik, Nowak, Papp, Wambach, and Zahed and of Jarosz and Nowak in the physics literature. We also show that pushing forward the Brown measure of x0+iσtx_{0}+i\sigma _{t} by a certain map Qt:ΩtRQ_{t}:\Omega _{t} \rightarrow {\mathbb {R}} gives the distribution of x0+σt.x_{0}+\sigma _{t}. We also establish a similar result relating the Brown measure of x0+iσtx_{0}+i\sigma _{t} to the Brown measure of x0+ctx_{0}+c_{t}, where ctc_{t} is the free circular Brownian motion.
Note:
  • 50 pages and 9 figures. Minor revisions in this version. To appear on Letters in Mathematical Physics
  • Brownian motion
  • density