From Steklov to Neumann and Beyond, via Robin: The Szegő Way. (7th August 2020)

• Record Type: Journal Article
• Authors: Freitas, Pedro; Laugesen, Richard S.
• Is Part Of: Canadian journal of mathematics. Volume 72:Number 4(2020)
• Page Start: 1024
• Page End: 1043
• Publication Date: 2020-08-07
• Subjects: 35P15, -- 30C70; Robin, -- Neumann, -- Steklov, -- vibrating membrane, -- absorbing boundary condition, -- conformal mapping; Mathematics -- Periodicals; Mathematics; Electronic journals; Periodicals; 510
• DOI: 10.4153/S0008414X19000154
• Languages: English
• ISSNs: 0008-414X

Abstract

Abstract: The second eigenvalue of the Robin Laplacian is shown to be maximal for the disk among simply-connected planar domains of fixed area when the Robin parameter is scaled by perimeter in the form $\unicode[STIX]{x1D6FC}/L(\unicode[STIX]{x1D6FA})$, and $\unicode[STIX]{x1D6FC}$ lies between $-2\unicode[STIX]{x1D70B}$ and $2\unicode[STIX]{x1D70B}$ . Corollaries include Szegő's sharp upper bound on the second eigenvalue of the Neumann Laplacian under area normalization, and Weinstock's inequality for the first nonzero Steklov eigenvalue for simply-connected domains of given perimeter. The first Robin eigenvalue is maximal, under the same conditions, for the degenerate rectangle. When area normalization on the domain is changed to conformal mapping normalization and the Robin parameter is positive, the maximiser of the first eigenvalue changes back to the disk.