Functional derivation of Casimir energy at non-zero temperature
  Performing functional integration of the free Lagrangian, we find the vacuum energy of a field. The functional integration is performed in a way which easily generalizes to systems at non-zero temperature. We use this technique to obtain the Casimir energy density and pressure at arbitrary temperatures. 
Avijit K. Ganguly (Indian Institute of Science, Bangalore), Palash B.   Pal (Saha Institute, Calcutta)