Papers by Tullio Ceccherini
Décompositions paradoxales des groupes de Burnside
Comptes Rendus Mathematique, 1998
Le nombre de Tarski T(G) d'un groupe G est defini comme une mesure de la complexite des decom... more Le nombre de Tarski T(G) d'un groupe G est defini comme une mesure de la complexite des decompositions paradoxales possibles de G. Nous exposons une methode pour estimer ces nombres, en termes de croissance relative ou de rayon spectral d'une marche aleatoire simple appropriee. En particulier, nous produisons une fonction f m telle que T(G) 2 generateurs d'exposant impair n ≥ 665.
Colloquium Mathematicum, 1997
Numerical estimates are given for the spectral radius of simple random walks on Cayley graphs. Em... more Numerical estimates are given for the spectral radius of simple random walks on Cayley graphs. Emphasis is on the case of the fundamental group of a closed surface, for the usual system of generators.
Simplicity of the fixed point algebra in O ∞ under special canonical action of a compact group
Approximately Inner and Centrally Free Commuting Squares of Type II1Factors and Their Classification
Journal of Functional Analysis, 1996
Abstract We investigate in detail the concepts of approximate innerness and central freeness for ... more Abstract We investigate in detail the concepts of approximate innerness and central freeness for commuting squares of type II1factors, with finite horizontal Jones index, introduced in [Po2], and prove a classification result showing that if[formula]is a nondegenerate approximately inner and centrally free commuting square of type II1factors withQ⊂Nstable andΓQ, Pstrongly amenable, then the commuting square is isomorphic to[formula], whereQst⊂Pstis the standard model of the inclusionQ⊂P.
Monatshefte f?r Mathematik, 2002
Consider the tesselation of the hyperbolic plane by m-gons, ℓ per vertex. In its 1-skeleton, we c... more Consider the tesselation of the hyperbolic plane by m-gons, ℓ per vertex. In its 1-skeleton, we compute the growth series of vertices, geodesics, tuples of geodesics with common extremities. We also introduce and enumerate holly trees, a family of reduced loops in these graphs. We then apply Grigorchuk's result relating cogrowth and random walks to obtain lower estimates on the spectral radius of the Markov operator associated with a symmetric random walk on these graphs.
Journal of Functional Analysis - J FUNCT ANAL, 1992
We show that the group of automorphisms of the Cuntz algebra 0, canonically associated to a group... more We show that the group of automorphisms of the Cuntz algebra 0, canonically associated to a group G of unitaries on the generating Hilbert space is ergodic if and only if G has no non-zero finite dimensional stable subspace; it is prime if G is strongly compact and more generally we give necessary and suficient conditions. If the defining representation of G is the direct sum of finite dimensional representations with determinant one the fixed point subalgebra Oc of 0, is a simple C*-algebra. These results extend in part to 0, results previously known for O,,n<oci.
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Papers by Tullio Ceccherini