Spectral optimization of Dirac rectangles
Philippe Briet, David Krejčiřı́k
Abstract
We are concerned with the dependence of the lowest positive eigenvalue of the Dirac operator on the geometry of rectangles, subject to infinite-mass boundary conditions. We conjecture that the square is a global minimizer under both the area or perimeter constraints. Contrary to the well-known non-relativistic analogs, we show that the present spectral problem does not admit explicit solutions. We prove partial optimization results based on a variational reformulation and newly established lower and upper bounds to the Dirac eigenvalue. We also propose an alternative approach based on symmetries of rectangles and a non-convex minimization problem; this implies a sufficient condition formulated in terms of a symmetry of the minimizer which guarantees the conjectured results.