The Electroweak Phase Transition: a Status Report *

The possibility that the observed cosmological baryon density might be a consequence of non-perturbative dynamics at the electroweak phase transition is one of the most exciting topics at the interface of particle physics and cosmology. However, determining the viability of electroweak baryogenesis in (minimal extensions of) the standard model requires knowledge of the equilibrium behavior of the electroweak phase transition, nonequilibrium dynamics around expanding bubble walls, and non-perturbative baryon violating processes in both the high and low temperature phases [1]. This talk will examine the current understanding of the electroweak phase transition. Determining the order of the phase transition, and the magnitudes of the latent heat, correlation lengths, and the baryon violation rate at the transition are some of the key questions. Viable baryogenesis scenarios require a first order transition with rapid suppression of baryon violating transitions in the low temperature phase [1, 2, 3]. Performing reliable quantitative calculations of electroweak transition properties is challenging, in part because there is important dynamics, both perturbative and non-perturbative, on many differing length scales. Approximation methods which have been applied to this problem include weak coupling perturbation theory (or mean field theory) [2, 4, 5], ǫ-expansions [6, 7, 8], and numerical simulations [9, 10, 11, 12]. Each of these approaches have significant (but differing) limitations; for example, ordinary perturbation theory is valid if the Higgs mass is much lighter than the W -boson mass, but does not appear to be trustworthy for the experimentally allowed range of possible Higgs masses. Nevertheless, all of these approaches