Nombres de Betti L2 et facteurs de type II1
Séminaire Bourbaki : volume 2002/2003, exposés 909-923, Astérisque, no. 294 (2004), Exposé no. 920, pp. 321-333.

Damien Gaboriau a montré récemment que les nombres de Betti L2 des feuilletages mesurés à feuilles contractiles sont des invariants de la relation d’équivalence associée. Sorin Popa a utilisé ce résultat joint à des propriétés de rigidité des facteurs de type II1 pour en déduire l’existence de facteurs de type II1 dont le groupe fondamental est trivial.

Damien Gaboriau showed recently that the L2 Betti numbers of measured foliations with contractile leaves are invariants of the associated equivalence relation. Sorin Popa used this result, together with rigidity properties of type II1 factors whose fundamental group is trivial.

Classification : 46L35, 57R30
Mot clés : nombres de Betti L2, feuilletage, facteur de type II1, groupe fondamental d’un facteur de type II1
Keywords: L2 Betti numbers, foliation, type II1 factor, fundamental group of a type II1 factor
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Connes, Alain. Nombres de Betti $L^2$ et facteurs de type ${\rm II}_1$, dans Séminaire Bourbaki : volume 2002/2003, exposés 909-923, Astérisque, no. 294 (2004), Exposé no. 920, pp. 321-333. https://www.numdam.org/item/SB_2002-2003__45__321_0/

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