Casimir free energy of a spherical cavity in a dielectric medium

An expression is derived for the Casimir free energy of a spherical cavity in a polar dielectric medium at finite temperature. In the process of the derivation the general problem of infinities and their renormalization in calculations of Casimir forces is analyzed. It is shown that the renormalized Casimir free energy has a minimum at a finite mesoscopic value of the cavity radius R=R-Min(Cas), with the repulsion for R <R-Min(Cas) and the attraction for R greater than or equal to R-Min(Cas). The implications of this result for the explanation of cavitation effects are discussed. (C) 1997 American Institute of Physics.