# On vanishing and localizing of transmission eigenfunctions near singular points: a numerical study

## TL;DR

This numerical study investigates how transmission eigenfunctions behave near singular points, revealing that they vanish or localize depending on the cusp angle, thus enriching spectral theory and impacting inverse scattering applications.

## Contribution

First numerical analysis of eigenfunction behavior near cusp singularities, showing vanishing or localization depending on the interior angle, with implications for spectral theory and inverse scattering.

## Key findings

- Eigenfunctions vanish near cusps with angles less than π
- Eigenfunctions localize near cusps with angles greater than π
- Vanishing and blowup orders are inversely proportional to the cusp angle

## Abstract

This paper is concerned with the intrinsic geometric structure of interior transmission eigenfunctions arising in wave scattering theory. We numerically show that the aforementioned geometric structure can be much delicate and intriguing. The major findings can be roughly summarized as follows. If there is a cusp on the support of the underlying potential function, then the interior transmission eigenfunction vanishes near the cusp if its interior angle is less than $\pi$, whereas the interior transmission eigenfunction localizes near the cusp if its interior angle is bigger than $\pi$. Furthermore, we show that the vanishing and blowup orders are inversely proportional to the interior angle of the cusp: the sharper the angle, the higher the convergence order. Our results are first of its type in the spectral theory for transmission eigenvalue problems, and the existing studies in the literature concentrate more on the intrinsic properties of the transmission eigenvalues instead of the transmission eigenfunctions. Due to the limitedness of the computing resources, our study is by no means exclusive and complete. We consider our study only in a certain geometric setup including corner, curved corner and edge singularities. Nevertheless, we believe that similar results hold for more general cusp singularities and rigorous theoretical justifications are much desirable. Our study enriches the spectral theory for transmission eigenvalue problems. We also discuss its implication to inverse scattering theory.