Extremal domains and P\\'{o}lya-type inequalities for the Robin Laplacian on rectangles and unions of rectangles
Pedro Freitas, James B. Kennedy · arXiv (Cornell University) · 2018
We show that eigenvalues of the Robin Laplacian with a positive boundary parameter $\\alpha$ on rectangles and unions of rectangtes satisfy P\\'{o}lya-type inequalities, albeit with an exponent smaller than that of the corresponding Weyl asympotics for a fixed domain. We determine the optimal exponents in either case, showing that they are different in the two situations. Our approach to proving these results includes a characterisation of the corresponding extremal domains for the $k$th eigenvalue in regions of the $(k,\\alpha)$-plane.