G. Scharf et Wf. Wreszinski, THE CASIMIR EFFECT AND FIELD QUANTIZATION WITH BOUNDARIES, Nuovo cimento della Società Italiana di Fisica. A. Nuclei, particles and fields, 107(12), 1994, pp. 2879-2883
A general method to calculate a well-defined energy density for the Ca
simir problem is described. It is applied to spherical and plain geome
tries with Dirichlet boundary conditions where an image method can be
used. Our main result is a very simple expression for the energy densi
ty of a spherical bag, a problem hitherto unsolved.