KK ‐theory of amalgamated free products of C *‐algebras |
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Authors: | Rune Eliasen |
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Institution: | Quantitative Research, The Danish Labour Market Supplementary Pension (ATP), Kongens V?nge 8, DK–3400 Hiller?d, DenmarkPhone: +45 48 20 42 78 |
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Abstract: | J. Cuntz has conjectured the existence of two cyclic six terms exact sequences relating the KK ‐groups of the amalgamated free product A 1 ?? B A 2 to the KK ‐groups of A 1, A 2 and B. First we establish automatic existence of strict and absorbing homomorphisms. Then we use this result to verify the conjecture when B is a countable direct sum of matrix algebras and the embeddings of B into A 1 and A 2 are quasiunital. Inspired by the proof we achieve the following nice classification result: A separable C *‐algebra B is a countable direct sum of matrix algebras if and only if the unitary group of the multiplier algebra U M (B) is compact in the strict topology. Finally we prove the conjecture when the amalgamated free product has the property that any asymptotically split extension of A 1 ?? B A 2 is split. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) |
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Keywords: | C *‐algebras KK ‐theory amalgamated free products absorbing homomorphisms countable direct sums of matrix algebras |
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