We investigate the statistical mechanics of a gas of spin-one particles with pair creation in a homogeneous magnetic field. It is shown that expansions for the thermodynamic potential and magnetization in fields below the mass scale of the constituent particles are well behaved. However, when the field is at or above the mass scale, an intrinsic pathology of the single-particle energy spectrum manifests itself in the statistical mechanics of the system. The nature of this intriguing phenomenon is discussed. © 1995 The American Physical Society.

• Received 6 June 1995

DOI:https://doi.org/10.1103/PhysRevD.52.7174