EFFECTIVE SCALAR FIELD-THEORY FOR THE ELECTROWEAK PHASE-TRANSITION

We investigate an effective model for the finite-temperature symmetry- restoration phase transition of the electroweak theory. It is obtained by dimensional reduction of the (3 + 1)-dimensional full theory and b y subsequent integration over all static gauge degrees of freedom. The resulting theory corresponds to a 3-dimensional 0(4) ferromagnet cont aining cubic and quartic terms of the field in its potential function. Possible nonperturbative effects of a magnetic screening mass are par ametrically included in the potential, We analyse the theory using mea n-field and numerical Monte Carlo (MC) simulation methods. At the valu e of the physical Higgs mass, m(H) = 37 GeV, considered in the present investigation, we find a discontinuous symmetry-restoring phase trans ition, We determine the critical temperature, order parameter jump, in terface tension and latent heat characteristics of the transition. The Monte Carlo results indicate a somewhat weaker first-order phase tran sition as compared to the mean-field treatment, demonstrating that non -perturbative fluctuations of the Higgs field are relevant, This effec t is especially important for the interface tension. Any observation o f hard first-order transition could result only from non-perturbative effects related to the gauge degrees of freedom.