
## 5. Dirac operators

1. ### Faber-Krahn for Dirac operator with infinite mass boundary condition

#### Problem 5.1.

[T. Ourmières-Bonafos] Prove or disprove that among all planar domains of a given area, the disk is the unique minimizer for the smallest positive eigenvalue $\nu_1(\Omega)$ of the Dirac problem with infinite mass boundary conditions \left\{ \begin{aligned} -\mathsf{i} \big(\partial_1 v - \mathsf{i}\partial_2 v\big) &= \nu u &&\mbox{in} \quad \Omega \,, \\ -\mathsf{i}\big(\partial_1 u + \mathsf{i}\partial_2 u\big) &= \nu v &&\mbox{in} \quad \Omega \,, \\ \mathsf{i}\big(n_1 + \mathsf{i} n_2\big) u &= v &&\mbox{on} \quad \partial\Omega \,, \end{aligned} \right. where $n = (n_1,n_2)^\top$ is the outer unit normal to $\Omega$.
A geometric lower bound for the first non-negative eigenvalue has been obtained by R. Benguria, S. Fournais, E. Stockmeyer, and H. Van Den Bosch [MR3625007]. Moreover, P. Antunes has provided numerical evidence to support that the disk is in fact the minimizer.

Cite this as: AimPL: Shape optimization with surface interactions, available at http://aimpl.org/shapesurface.