2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48250The use of classical thermal field to approximate real-time quantum thermal field theory is discussed. For a λϕ^4 theory, it is shown that the classical Rayleigh-Jeans divergence can be canceled with the appropriate counterterms, and a comparison is made between the classical and quantum perturbative expansion. It is explained why Hard Thermal Loops prevent the same method to work for gauge theories.5 pages, 2 eps figures, talk presented at the 5th International Workshop on Thermal Field Theories and Their Applications, Regensburg, Germany, August 10-14, 1998High Energy Physics - Phenomenologytext