PERTURBATIVE STUDY OF THE ELECTROWEAK PHASE TRANSITION

The electroweak phase transition is studied at finite temperature. The effective action is given to higher orders, including wave function correction factors and the full $g^4,{\lambda }^2$ effective potential. An upper bound for the Higgs mass $m_H\approx 70GeV$ is concluded for the reliability of the perturbative approach. A gauge invariant treatment of the phase transition is presented.