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Abért-Weiss have shown that the Bernoulli shift sΓ of a countably infinite group Γ is weakly contained in any free measure preserving action a of Γ. Proving a conjecture of Ioana we establish a strong version of this result by showing that sΓ × a is weakly equivalent to a. Using random Bernoulli shifts introduced by Abért-Glasner-Virag we generalized this… (More)

Ultraproducts of measure preserving actions of countable groups are used to study the graph combinatorics associated with such actions, including chromatic, independence and matching numbers. Applications are also given to the theory of random colorings of Cayley graphs and sofic actions and equivalence relations.

- Brandon Seward, Robin D. Tucker-Drob
- Ann. Pure Appl. Logic
- 2016

We show that for any infinite countable group G and for any free Borel action G y X there exists an equivariant class-bijective Borel map from X to the free part Free(2G) of the 2-shift G y 2G. This implies that any Borel structurability which holds for the equivalence relation generated by Gy Free(2G) must hold a fortiori for all equivalence relations… (More)

A countable group Γ is called shift-minimal if every non-trivial measure preserving action of Γ weakly contained in the Bernoulli shift Γ y ([0, 1] , λ ) is free. We show that any group Γ whose reduced C∗-algebra Cr(Γ) admits a unique tracial state is shift-minimal, and that any group Γ admitting a free measure preserving action of cost> 1 contains a finite… (More)

This note answers a question of Kechris: if H < G is a normal subgroup of a countable group G, H has property MD and G/H is amenable and residually finite then G also has property MD. Under the same hypothesis we prove that for any action a of G, if b is a free action of G/H, and bG is the induced action of G then CInd G H(a|H)×bG weakly contains a.… (More)

We classify the ergodic invariant random subgroups of inductive limits of finite alternating groups.

A measure preserving action of a countably in nite group Γ is called totally ergodic if every in nite subgroup of Γ acts ergodically. For example, all mixing and mildly mixing actions are totally ergodic. This note shows that if an action of Γ is totally ergodic then there exists a nite normal subgroup N of Γ such that the stabilizer of almost every point… (More)

We study actions of countable discrete groups which are amenable in the sense that there exists a mean on X which is invariant under the action of G. Assuming that G is nonamenable, we obtain structural results for the stabilizer subgroups of amenable actions which allow us to relate the first `-Betti number of G with that of the stabilizer subgroups. An… (More)

Abért and Weiss have shown that the Bernoulli shift s0 of a countably infinite group 0 is weakly contained in any free measure preserving action a of 0. Proving a conjecture of Ioana, we establish a strong version of this result by showing that s0 × a is weakly equivalent to a. Using random Bernoulli shifts introduced by Abért, Glasner, and Virag, we… (More)

The last two decades have seen the emergence of a theory of set theoretic complexity of classification problems in mathematics. In these lectures we will discuss recent developments concerning the application of this theory to classification problems in ergodic theory. The first lecture will be devoted to a general introduction to this area. The next two… (More)