We reconsider the vacuum (Casimir) energy of a massive scalar field obeying Dirichlet boundary conditions inside a spherical cavity. Using zeta-function regularization, we carefully recalculate the analytic part of the zeta function via the uniform asymptotic expansion of the modified Bessel functions. We correct a sign error present in an earlier calculation that affected the large-mass behavior. The renormalized vacuum energy is shown to vanish as m→∞, as required on physical grounds. Numerical results reveal that the energy changes sign several times as a function of the cavity radius.
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Bordag et al. (2026) studied this question.
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