The uniqueness of the spectral flow on spaces of unbounded self--adjoint Fredholm operators
Abstract
Description
We discuss several natural metrics on spaces of unbounded self--adjoint operators and their relations, among them the Riesz and the graph metric. We show that the topologies of the spaces of Fredholm operators resp. invertible operators depend heavily on the metric. Nevertheless we prove that in all cases the spectral flow is up to a normalization the only integer invariant of non-closed paths which is path additive and stable under homotopies with endpoints varying in the space of invertible self-adjoint operators.
Furthermore we show that for certain Riesz continuous paths of self--adjoint Fredholm operators the spectral flow can be expressed in terms of the index of the pair of positive spectral projections at the endpoints.
Finally we review the Cordes--Labrousse theorem on the stability of the Fredholm index with respect to the graph metric in a modern language and we generalize it to the Clifford index and to the equivariant index.
32 pages, 2 figures; to appear in January 2005 in an AMS Contemporary Math Proceedings volume on 'Spectral Geometry of Manifolds with Boundary', edited by B. Booss--Bavnbek, G. Grubb and K.P. Wojciechowski
32 pages, 2 figures; to appear in January 2005 in an AMS Contemporary Math Proceedings volume on 'Spectral Geometry of Manifolds with Boundary', edited by B. Booss--Bavnbek, G. Grubb and K.P. Wojciechowski