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Séminaire de Probabilités XLIV, Catherine Donati-Martin, Antoine Lejay, Alain Rouault (Ed.) (2012) 191-206
Spectral distribution of the free unitary Brownian motion: another approach
Nizar Demni 1, Taoufik Hmidi 1
(2012)

We revisit the description provided by Ph. Biane of the spectral measure of the free unitary Brownian motion. We actually construct for any $t \in (0,4)$ a Jordan curve $\gamma_t$ around the origin, not intersecting the semi-axis $[1,\infty[$ and whose image under some meromorphic function $h_t$ lies in the circle. Our construction is naturally suggested by a residue-type integral representation of the moments and $h_t$ is up to a Möbius transformation the main ingredient used in the original proof. Once we did, the spectral measure is described as the push-forward of a complex measure under a local diffeomorphism yielding its absolute-continuity and its support. Our approach has the merit to be an easy yet technical exercise from real analysis.
1 :  Institut de Recherche Mathématique de Rennes (IRMAR)
CNRS : UMR6625 – Université de Rennes 1 – École normale supérieure de Cachan - ENS Cachan – Institut National des Sciences Appliquées (INSA) : - RENNES – Université de Rennes II - Haute Bretagne
Théorie ergodique
Equations aux dérivées partielles
Mathématiques/Algèbres d'opérateurs

Mathématiques/Analyse classique
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