Fixed Convex-Lens Spectral Constants: M\"obius Reduction, Sharp Model Theorems, and Angle-Dependent Bounds
For the intersection of two disks meeting at angle $2\alpha$, let $C(\alpha)$ be the least constant in the associated spectral-set inequality. We give a self-contained M"obius reduction to the corresponding numerical-range problem on a sector and determine the sharp constant for affine square-zero operators $B=\lambda...