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Mehrdad Kalantar
University of Houston
Canonical nuclear embeddings of reduced C*-algebras of exact groups
October 2, 2015 1pm, 646 PGH
Abstract
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By a result of Kirchberg, every exact C*-algebra A can be embedded
into a nuclear C*-algebra B. In fact, Kirchberg and Phillips later proved that
the nuclear C*-algebra B can always be taken to be the Cuntz algebra on two generators.
However, in general, the nuclear embeddings that are guaranteed to exist by the
above results can be difficult to realize. Additionally, the image of an exact
C*-algebra under a nuclear embedding can be relatively small and, consequently,
properties like simplicity and primeness are not necessarily reflected in the
larger C*-algebra. Hence, for a given exact C*-algebra, it is natural to seek
for a more canonical nuclear embedding. In this direction, Ozawa proved
that the reduced C*-algebra C_r*(F_n) of the free group F_n on n generators
can be embedded into a nuclear C*-algebra that is contained in the injective envelope of C_r*(F_n).
This provides a rather “tight” nuclear embedding of the reduced C*-algebra C_r*(F_n). He furthermore conjectured that it should be possible to construct such an embedding for any exact C*-algebra. We prove Ozawa’s conjecture for the reduced C*-algebra of every discrete exact group.
This is joint work with Matthew Kennedy.
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