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Boundary integral exterior calculus

E. Schulz, R. Hiptmair, S. Kurz

Journal of the European Mathematical Society, 2025

Abstract

We report a surprising and deep structural property of boundary integral operators occurring in first-kind boundary integral equations associated with Hodge–Dirac and Hodge–Laplace operators for de Rham Hilbert complexes on a bounded domain Ω in a Riemannian manifold. We show that, as regards their induced bilinear forms, those boundary integral operators are Hodge–Dirac and Hodge–Laplace operators in the weak sense, this time set in a trace de Rham Hilbert complex on the boundary ∂Ω whose underlying spaces of differential forms are equipped with non-local inner products defined through layer potentials. On the way to this main result we conduct a thorough analysis of layer potentials in operator-induced trace spaces and derive representation formulas.

This paper is the culmination of my PhD research at ETH Zürich. We establish that first-kind boundary integral operators for Hodge–Dirac operators are themselves Hodge–Dirac operators in trace de Rham complexes, equipped with non-local inner products defined through boundary potentials.

The framework unifies and extends classical results for scalar and vector boundary integral equations to differential forms of arbitrary degree on manifolds.