Elliptic Boundary Value Problems and Partial Group Actions
Abstract
We consider a smooth compact manifold with boundary, , embedded in a smooth manifold of the same dimension on which an amenable group acts by isometries. We do not assume to be invariant under . This results in a {\em partial action} of on : For we let and obtain diffeomorphisms . We assume that any two images of under either coincide or are disjoint and that only finitely many lie in . The spherical blow-up of these images of in yields a manifold with boundary consisting of finitely many components. Moreover, inherits a partial action of~. We can then define the -algebra of operators on , generated by the algebra of operators of order and type zero in Boutet de Monvel's calculus on and partial isometries associated with the partial action. Denote by its symbol space. If the partial action of on Prim is topologically free, we find a criterion for the Fredholm property of the operators in . Moreover, we obtain the classification of the elliptic elements in modulo stable homotopies: For If is finitely generated and of polynomial growth, then the elements associated with the second summand do not contribute to the index.
Cite
@article{arxiv.2605.29750,
title = {Elliptic Boundary Value Problems and Partial Group Actions},
author = {Eske Ewert and Anton Yu. Savin and Elmar Schrohe},
journal= {arXiv preprint arXiv:2605.29750},
year = {2026}
}