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Algebraic and topological K-theory, relations with topology, commutative algebra, and operator algebras

18 votes
3 answers
1k views

Periodicity theorems in (generalized) cohomology theories

It is well-known that topological K-theory is blessed with the Bott periodicity theorem, which specifies an isomorphism between $K^2(X)$ and $K^0(X)$ (where $K^n$ is defined from $K^0$ by taking suspe …
Paul Siegel's user avatar
  • 29.2k
16 votes
2 answers
1k views

Is there an effective way to calculate K-theory using Morse functions?

Let $M$ be a compact manifold and let $f$ be a Morse function with exactly one critical point at each critical level. Then one can recover a CW-complex with the homotopy type of $M$ from just the cri …
Paul Siegel's user avatar
  • 29.2k
11 votes
4 answers
1k views

Relative K-theory and split exact sequences of C* algebras

Let $A$ be a C* algebra, $J$ an ideal, $\pi: A \to A/J$ the quotient map. Recall that the relative K theory group $K_0(A, A/J)$ consists of equivalence classes of triples $(p,q,x)$ where $p$ and $q$ …
Paul Siegel's user avatar
  • 29.2k
7 votes
2 answers
524 views

Integrality of the canonical trace and topology

Let $G$ be a discrete group and consider the reduced group C* algebra $C_r^\ast(G)$, viewed as an algebra of bounded operators on $\ell^2(G)$ by the regular representation. The canonical trace on $C_ …
Paul Siegel's user avatar
  • 29.2k
7 votes
1 answer
388 views

What are the relations in the unbounded model of K-homology?

I have posed this question to some experts at my university who would probably know the answer if there were a complete one, so my expectations are limited. It's possible that the question deserves t …
Paul Siegel's user avatar
  • 29.2k
7 votes
2 answers
765 views

Can anyone calculate KK(A,B) when neither A or B are the complex numbers?

Here I am referring to Kasparov's KK-theory, a bivariant functor on the category of separable C* algebras. It is well known that $KK(A, \mathbb{C})$ is K-homology and $KK(\mathbb{C}, B)$ is K-theory, …
Paul Siegel's user avatar
  • 29.2k