Journal of the Ramanujan Mathematical Society

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Factors from Ergodic Theory and Group-Subgroup Subfactors


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1 Matematisk Institut, Ny Munkegade, 8000 AARHUS C, Denmark
     

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We show that the subfactors arising from factor maps between measure preserving ergodic dynamical systems, where the group acting is discrete and amenable, are the same as the subfactors arising as fixed point algebra inclusions coming from a finite group and a subgroup acting freely on the hyperfinite II1 -factor. This conclusion is used to obtain new numbers in the set Λ(M,N) introduced by Popa, in case of a group-subgroup subfactor.
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  • Factors from Ergodic Theory and Group-Subgroup Subfactors

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Authors

Sergey Dorofeev
Matematisk Institut, Ny Munkegade, 8000 AARHUS C, Denmark

Abstract


We show that the subfactors arising from factor maps between measure preserving ergodic dynamical systems, where the group acting is discrete and amenable, are the same as the subfactors arising as fixed point algebra inclusions coming from a finite group and a subgroup acting freely on the hyperfinite II1 -factor. This conclusion is used to obtain new numbers in the set Λ(M,N) introduced by Popa, in case of a group-subgroup subfactor.