An Index Theorem for Gauge-invariant Families: the Case of Solvable Groups

We define the gauge-equivariant index of a family of elliptic operators invariant with respect to the free action of a family G → B of Lie groups (these families are called “gauge-invariant families” in what follows). If the fibers of G → B are simply-connected and solvable, we compute the Chern character of the gauge-equivariant index, the result being given by an AtiyahSinger type formula that incorporates also topological information about the bundle G → B. The algebras of invariant pseudodifferential operators that we study, ψ inv (Y ) and Ψ inv (Y ), are generalizations of “parameter dependent” algebras of pseudodifferential operators (with parameter in R), so our results provide also an index theorem for elliptic, parameter dependent pseudodifferential operators. We apply these results to study Fredholm boundary conditions on a simplex.