This paper continues the project started in [13] where Poincaré duality in K -theory was studied for singular manifolds with isolated conical singularities. Here, we extend the study and the results to general stratified pseudomanifolds. We review the axiomatic definition of a smooth stratification S of a topological space X and we define a groupoid T S X , called the S-tangent space. This groupoid is made of different pieces encoding the tangent spaces of strata, and these pieces are glued into the smooth noncommutative groupoid T S X using the familiar procedure introduced by A. Connes for the tangent groupoid of a manifold. The main result is that C * (T S X) is Poincaré dual to C(X), in other words, the S-tangent space plays the role in K -theory of a tangent space for X . 58B34, 46L80, 19K35, 58H05, 57N80; 19K33, 19K56, 58A35
IntroductionThis paper takes place in a longstanding project aiming to study index theory and related questions on stratified pseudomanifolds using tools and concepts from noncommutative geometry.The key observation at the beginning of this project is that in its K -theoritic form, the Atiyah-Singer index theorem [2] involves ingredients that should survive to the singularities allowed in a stratified pseudomanifold. This is possible, from our opinion, as soon as one accepts reasonable generalizations and new presentation of certain classical objects on smooth manifolds, making sense on stratified pseudomanifolds.The first instance of these classical objects that need to be adapted to singularities is the notion of tangent space. Since index maps in [2] are defined on the K -theory of the tangent spaces of smooth manifolds, one must have a similar space adapted to stratified pseudomanifolds. Moreover, such a space should satisfy natural requirements. It should coincide with the usual notion on the regular part of the pseudomanifold and incorporate in some way copies of usual tangent spaces of strata, while keeping enough smoothness to allow interesting computations. Moreover, it should be Poincaré dual In [13], we introduced a candidate to be the tangent space of a pseudomanifold with isolated conical singularities. It appeared to be a smooth groupoid, leading to a noncommutative C * -algebra, and we proved that it fulfills the expected K -duality.In [22], the second author interpreted the duality proved in [13] as a principal symbol map, thus recovering the classical picture of Poincaré duality in K -theory for smooth manifolds. This interpretation used a notion of noncommutative elliptic symbols, which appeared to be the cycles of the K -theory of the noncommutative tangent space.In [14], the noncommutative tangent space together with other deformation groupoids was used to construct analytical and topological index maps, and their equality was proved. As expected, these index maps are straight generalizations of those of [2] for manifolds.The present paper is devoted to the construction of the noncommutative tangent space for a general stratified pseudomanifold and the proof of ...