Derivative expansion for the electromagnetic Casimir free energy at high temperatures

C. D. FOSCO; F. LOMBARDO; F.D. MAZZITELLI

PHYSICAL REVIEW D - PARTICLE AND FILDS

APS

Lugar: New York; Año: 2015 vol. 92 p. 1250071 - 12500711

0556-2821

We study the contribution of the thermal zero modes to the Casimir free energy in the case of a fluctuating electromagnetic (EM) field in the presence of real materials described by frequency-dependent, local and isotropic permittivity (ε) and permeability (μ) functions. Those zero modes, present at any finite temperature, become dominant at high temperatures since the theory is dimensionally reduced. Our work, within the context of the derivative expansion (DE) approach, focuses on the emergence of nonanalyticities in that dimensionally reduced theory. We conclude that the DE is well defined whenever the function ΩðωÞ, defined by 1⁄2ΩðωÞ2 ≡ ω2εðωÞ, vanishes in the zero-frequency limit for at least one of the two material media involved.