Group C-algebras as Compact Quantum Metric Spaces
نویسنده
چکیده
Let l be a length function on a group G, and let Ml denote the operator of pointwise multiplication by l on l(G). Following Connes, Ml can be used as a “Dirac” operator for C ∗ r (G). It defines a Lipschitz seminorm on C∗ r (G), which defines a metric on the state space of C∗ r (G). We investigate whether the topology from this metric coincides with the weak-∗ topology (our definition of a “compact quantum metric space”). We give an affirmative answer for G = Z when l is a word-length, or the restriction to Z of a norm on R. This works for C∗ r (G) twisted by a 2-cocycle, and thus for non-commutative tori. Our approach involves Connes’ cosphere algebra, and an interesting compactification of metric spaces which is closely related to geodesic rays.
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