The Electroweak Phase Transition

The electroweak phase transition is investigated by means of the perturbatively calculated high temperature effective potential. An analytic result to order $g^4,\lambda^2$ is presented for the Abelian Higgs model, the SU(2)-Higgs model and the standard model and a complete on-shell renormalization at zero temperature is performed. Higher order corrections are found to increase the strength of the first order phase transition in the non-Abelian model, opposite to the Abelian case. This effect is traced back to the infrared contributions from the typical non-Abelian diagrams. The dependence of several phase transition parameters on the Higgs mass is analysed in detail. A new, gauge invariant, approach based on the composite field $\Phi^\dagger\Phi$ is introduced. This method, which supports the above Landau gauge results numerically, permits a conceptually simpler treatment of the thermodynamics of the phase transition. In particular, it enables a straightforward comparison with lattice data and the application of the Clausius-Clapeyron equation to the electroweak phase transition.