Finite Temperature Effective Potential to Order $g^4,\la^2$ and the Electroweak Phase Transition

The standard model effective potential is calculated at finite temperature to order $g^4,\la^2$ and a complete zero temperature renormalization is performed. In comparison with lower order calculations the strength of the first order phase transition has increased dramatically. This effect can be traced back to infrared contributions from typical non-Abelian diagrams and to the infrared behaviour of the scalar sector close to the critical temperature. Several quantities, e.g. surface tension, latent heat and field expectation value are analyzed for an SU(2)-Higgs model and for the full standard model in detail. An explicit formula enabling further analytic or numerical study is presented. (DESY-94-025)