3 - Fold Local index theorem

Although this is a slightly modified version of the paper [23], it has to be seen as preliminary work.

3-Fold Local Index Theorem means Local (Local (Local Index Theorem))). Local Index Theorem is the Connes-Moscovici local index theorem [4], [5]. The second ’’Local” refers to the cyclic homology localised to a certain separable subring of the ground algebra, while the last one refers to Alexander-Spanier type cyclic homology. Localised cyclic homology had already appeared in the literature, see Connes [3], Karoubi [9] [10], Loday [12].

The Connes-Moscovici work is based on the operator R.(A) = P - e associated to the elliptic pseudo-differential operator A on the smooth manifold M, where P . e are idempotents, see [4], Pg. 353.

The operator R(A) has two main merits: it is a smoothing operator and its distributional kernel is situated in an arbitrarily small neigh- bourhood of the diagonal in M x M.

The operator R(A) has also two setbacks: -i) it is not an idempotent and therefore it does not have a genuine Connes-Karoubi-Chern character in the absolute cyclic homology of the algebra of smoothing operators, see Connes [2], [3], Karoubi [9] [10] ; -ii) even if it were an idempotent, its Connes-Karoubi-Chern character would belong to the cyclic homology of the algebra of smoothing operators with arbitrary supports, which is trivial.

This paper presents a new solution to the difficulties raised by the two setbacks.

For which concerns -i), we show that although R(A) is not an idem- potent, it satisfies the identity (R(A))2 = R(-A) - [R(A).e + e.R(A)]. We show that the operator R(A) has a genuine Chern character provided the cyclic homology complex of the algebra of smoothing operators is localised to the separable sub-algebra A = C + C.e, see Section 7.1.

For which concerns -ii), we introduce the notion of local cyclic homology; this is constructed on the foot-steps of the Alexander-Spanier homology, i.e. by filtering the chains of the cyclic homology complex of the algebra of smoothing operators by their distributional support, see Section 6.

Using these new instruments, we give a reformulation of the Connes- Moscovici local Index Theorem, see Theorem 8.1, Section 8. As a corollary of this theorem, we show that the local cyclic homology of the algebra of smoothing operators is at least as big as the Alexander-Spanier homology of the base manifold.

The present reformulation of Connes-Moscovici local index theorem opens the way to new investigations, see Section 9.