Shape sensitivity analysis of Neumann-Poincaré eigenvalues
Matteo Dalla Riva, Pier Domenico Lamberti, Paolo Luzzini, Paolo Musolino
TL;DR
This paper establishes that Neumann-Poincaré eigenvalues depend real-analytically on boundary shape perturbations and derives the explicit first-order derivative of symmetric functions of eigenvalues under infinite-dimensional perturbations. The approach hinges on pulling back to a fixed boundary, employing Riesz projectors for symmetrizable operators, and expressing derivatives through a matrix representation on the eigen-subspace, with the derivative formula ultimately expressed via plasmonic eigenfunctions on the boundary. Applications include a Rellich-Pohožaev-type identity for dilations and a sphere-critically-for-sums result for NP-eigenvalues in any dimension $n\ge 3$, supporting conjectural optimality statements and generalizing prior Grieser and Zolésio findings. The work thus provides a rigorous perturbation-theory framework for NP-spectrum optimization, with potential implications for plasmonic design and boundary-shape optimization. Overall, the results extend analytic perturbation theory to symmetrizable, infinite-dimensional perturbations and establish concrete tools for understanding how geometry governs spectral behavior in boundary integral operators.
Abstract
This paper concerns the eigenvalues of the Neumann-Poincaré operator, a boundary integral operator associated with the harmonic double-layer potential. Specifically, we examine how the eigenvalues depend on the support of integration and prove that the map associating the support's shape to the eigenvalues is real-analytic. We then compute its first derivative and present applications of the resulting formula. The proposed method allows for handling infinite-dimensional perturbation parameters for multiple eigenvalues and perturbations that are not necessarily in the normal direction.
