2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48785In this paper the phase structure of the massive $λϕ^4$ model at finite temperature ($T \neq 0$) is investigated by applying a resummation method inspired by the renormalization-group (RG) improvement to the one-loop effective potential. The resummation method a la RG-improvement is shown to work quite succesfully by resumming up systematically large correction-terms of $O(λT/μ)$ and of $O(λ(T/μ)^2)$. The temperature-dependent phase transition of the model is shown to proceed through the second order transition. The critical exponents are determined analytically and are compared with those in other analyses.6 pages, Latex file with sprocl.sty and epsf.sty, including 1 figure (eps.file). Talk presented at 1998 YITP-Workshop on QCD and Hadron Physics. To be published in ProceedingsHigh Energy Physics - Phenomenologytext