We study the analogue, in orbit equivalence, of free product decompositions and free indecomposability for countable groups. We introduce the (orbit equivalence invariant) notion of freely indecomposable (FI) standard probability measure preserving equivalence relations and establish a criterion to check it, namely non-hyperfiniteness and vanishing of the first L2-Betti number. We obtain Bass–Serre rigidity results, i.e. forms of uniqueness in free product decompositions of equivalence relations with (FI) components. The main features of our work are weak algebraic assumptions and no ergodicity hypothesis for the components. We deduce, for instance, that a measure equivalence between two free products of non-amenable groups with vanishing first l2-Betti numbers is induced by measure equivalences of the components. We also deduce new classification results in orbit equivalence and II1 factors.
@article{10_4171_ggd_150,
author = {Aur\'elien Alvarez and Damien Gaboriau},
title = {Free products, orbit equivalence and measure equivalence rigidity},
journal = {Groups, geometry, and dynamics},
pages = {53--82},
year = {2012},
volume = {6},
number = {1},
doi = {10.4171/ggd/150},
url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/150/}
}
TY - JOUR
AU - Aurélien Alvarez
AU - Damien Gaboriau
TI - Free products, orbit equivalence and measure equivalence rigidity
JO - Groups, geometry, and dynamics
PY - 2012
SP - 53
EP - 82
VL - 6
IS - 1
UR - http://geodesic.mathdoc.fr/articles/10.4171/ggd/150/
DO - 10.4171/ggd/150
ID - 10_4171_ggd_150
ER -
