Casimir energy of a scalar field with a space-dependent mass distribution

The Casimir energy is evaluated for a free scalar field that has a mass term m²(x₁), depending on one space coordinate x₁. The formalism for evaluating the Casimir energy is developed for the case of m²(x₁) finite everywhere in d-dimensional space-time. The case with $\text{m}{}^2\text{(x}{}_1\text{) = m}{}_0{}^2\text{θ(}\text{1}\text{2}\text{L}\text{-|x}{}_1\text{|) + m}{}_{\mathrm{\infty }}{}^2\text{θ (|x}{}_1\text{| -}\text{1}\text{2}\text{L}$) is explicity evaaluated for any value of 1197 1568 V m₀ and m_∞ without any approximation. The result consists of valume energy terms, a surface term, and a non-leading term. Most of the UV divergences are in the volume energy terms and renormalize the coupling constants of the underlying theory. The surface energy term is finite for d ? 4 and divergent for d ? 5 due to the boundaries being sharp. A closed finite expression is obtained for the non-leading term. Our results are shown to reproduce the known Casimir energies for the limiting cases, 1197 15 m₀ → ∞ andm_∞ → ∞.