Improved calculation of effective potential and symmetry-restored transition in Higgs model

Early in the 1970s, some authors suggested that the electroweak gauge symmetry should be restored at high enough temperature and density. Recently the electroweak phase transition has attracted much attention, because it is of crucial importance for the baryon asymmetry of the universe. So it is required to discuss the electroweak phase transition in detail. The basical tool for studying the phase transition is effective potential, and naive calculation of the effective potential has two difficulties. Here we will propose a self-consistent calculation of the effecitve potential by the resummation of hard thermal loops, and use this improved method to discuss the symmetry-restored transition in the Higgs model.