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SUMMARY:Approximate equivalence of measure-preserving actions - Andreas Aa
 serud (Cardiff University)
DTSTART:20170309T140000Z
DTEND:20170309T150000Z
UID:TALK71433@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:I will talk about measure-preserving actions of countable disc
 rete groups on probability spaces. Classically\, one mainly considers two 
 notions of equivalence of such actions\, namely conjugacy (or isomorphism)
  and orbit equivalence\, both of which have nice descriptions in the langu
 age of von Neumann algebras.&nbsp\;I will briefly discuss this classical f
 ramework before going into some new notions of equivalence of actions. The
 se are approximate versions of conjugacy and orbit equivalence that were r
 ecently introduced and investigated by Sorin Popa and myself\, and which c
 an&nbsp\;most easily be defined in terms of ultrapowers of von Neumann alg
 ebras. I will discuss superrigidity within this new framework\, and&nbsp\;
 will also compare approximate conjugacy to (classical) conjugacy for actio
 ns of various classes of groups. This talk is based on joint work with Sor
 in Popa.<br><br><br><br><br>
LOCATION:Seminar Room 2\, Newton Institute
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