H. Kleinert et A. Zhuk, THE CASIMIR EFFECT AT NONZERO TEMPERATURES IN A UNIVERSE WITH TOPOLOGY S-1XS-1XS-1, Theoretical and mathematical physics, 108(3), 1996, pp. 1236-1248
We investigate the influence of finite-size effects on the free energy
of mass and massless scalar fields at nonzero temperatures in a unive
rse with the topology of a three-dimensional torus. The renormalized f
ree energy and the resulting energy density and pressure are found. Th
eir physical consequences are discussed.