Casimir Energies of Cylinders: Universal Function

TL;DR

This paper presents new exact and numerical results for the Casimir energies of waveguides with various polygonal cross sections, revealing a potential universal behavior of energy dependence on shape, and compares these with the proximity force approximation.

Contribution

It provides the first exact formulas for interior Casimir energies of certain polygonal waveguides and explores their universal shape dependence.

Findings

Exact formulas for triangular and rectangular cross sections.

Universal behavior of Casimir energy as a function of shape.

Comparison showing deviations from proximity force approximation.

Abstract

New exact results are given for the interior Casimir energies of infinitely long waveguides of triangular cross section (equilateral, hemiequilateral, and isosceles right triangles). Results for cylinders of rectangular cross section are rederived. In particular, results are obtained for interior modes belonging to Dirichlet and Neumann boundary conditions (TM and TE modes). These results are expressed in rapidly convergent series using the Chowla-Selberg formula, and in fact may be given in closed form, except for general rectangles. The energies are finite because only the first three heat-kernel coefficients can be nonzero for the case of polygonal boundaries. What appears to be a universal behavior of the Casimir energy as a function of the shape of the regular or quasi-regular cross-sectional figure is presented. Furthermore, numerical calculations for arbitrary right triangular cross sections suggest that the universal behavior may be extended to waveguides of general polygonal cross sections. The new exact and numerical results are compared with the proximity force approximation (PFA).