The zero-point (Casimir) energy of free vector (gluon) fields confined to a spherical cavity (bag) is computed. The result is quadratically divergent, but it is argued that this divergence may be absorbed by a suitable renormalization of a constant force parameter. If so, the result for eight gluons is $E=+\frac{0.51}{a}$. This result is substantially larger than that for a spherical shell (where both interior and exterior modes are present), and so affects Johnson's model of the quantum-chromodynamic vacuum. It is also smaller than, and of opposite sign to, the value used in bag-model phenomenology, so it will have important implications there.

• Received 27 March 1980

DOI:https://doi.org/10.1103/PhysRevD.22.1441