In this talk, we shall consider equivariant subproduct system of Hilbert spaces and their Toeplitz and Cuntz–Pimsner algebras. We will provide results about their topological invariants through K(K)-theory. More specifically, we will show that the Toeplitz algebra of the subproduct system of an SU(2)-representation is equivariantly KKequivalent to the algebra of complex numbers so that the (K)K- theory groups of the Cuntz–Pimsner algebra can be effectively computed using a Gysin exact sequence involving an analogue of the Euler class of a sphere bundle. Finally, we will discuss why and how C*-algebras in this class satisfy KK-theoretic Poincaré duality.[-]

The right side of the Baum-Connes conjecture is the $K$-theory of the reduced $C^*$-algebra $C^*_{red} (G)$ of the group $G$. This algebra is the completion of the algebra $L^1(G)$ in the norm of the algebra of operators acting on $L^2(G)$. If we complete the algebra $L^1(G)$ in the norm of the algebra of operators acting on $L^p(G)$ we will get the Banach algebra $C^{*,p}_{red}(G)$. The $K$-theory of this algebra serves as the right side of the $L^p$-version of the Baum-Connes conjecture. The construction of the left side and the assembly map in this case requires a little bit of techniques of asymptotic morphisms for Banach algebras. A useful category of Banach algebras for this purpose includes all algebras of operators acting on $L^p$-spaces (which may be called $L^p$-algebras).
The current joint work in progress with Guoliang Yu aims at proving the following result:
The $L^p$-version of the Baum-Connes conjecture with coefficients in any $L^p$-algebra is true for any discrete group $G$ which admits an affine-isometric, metrically proper action on the space $X = l^p(Z)$, where $Z$ is a countable discrete set, so that the linear part of this action is induced by a measure-preserving action of $G$ on $Z$.
I will discuss the techniques involved in this work.[-]