The paper presents a first step towards a family index theorem for classical self-adjoint boundary value problems. We address here the simplest nontrivial case of manifolds with boundary, namely the case of two-dimensional manifolds. The first result of the paper is an index theorem for families of first order self-adjoint elliptic differential operators with local boundary conditions, parametrized by points of a compact topological space X. We compute the K 1 (X)valued index in terms of the topological data over the boundary. The second result is universality of the index: we show that the index is a universal additive homotopy invariant for such families, if the vanishing on families of invertible operators is required.
Contents1. ind a (γ 1 ) = ind a (γ 2 ).
Family index for self-adjoint unbounded operatorsIn order to deal with unbounded self-adjoint operators (in particular, with self-adjoint differential operators) directly, one needs an analogue of the Atiyah-Singer theory [2]. Cf.[5], [7], [9]. This section is devoted to such an analogue adapted to our framework. The functor K 1 . Let H be a Hilbert space. Denote by B(H) the space of bounded linear operators H → H with the norm topology.