Electroweak Baryogenesis without the Phase Transition

The baryogenesis is reanalyzed based on the model by A.G.Cohen et al., in which the lepton number, generated by the neutrinos' scattering from the bubble walls appearing in the development of the electroweak phase transition, is converted to the baryon number excess through the sphaleron transition. A formula obtained in this paper on the lepton number production rate is correct for the both thin and thick walls within the linear approximation. Investigation on the time-devel...

Scalar fields can play a dominant role in the dynamics of the Universe until shortly before nucleosynthesis. Examples are provided by domination by a kinetic mode of a scalar field, which may be both the inflaton and the late time `quintessence', and also by more conventional models of reheating. The resultant modification to the pre-nucleosynthesis expansion rate can allow solely an asymmetry in right handed electrons to produce a net baryon asymmetry when reprocessed by the...

The electroweak sphaleron process breaks the baryon number conservation within the realms of the Standard Model of particle physics (SM). Recently, it is pointed out that its decoupling may provide the out-of-equilibrium condition required for baryogenesis. In this paper, we study such a scenario taking into account the baryon-number wash-out effect of the sphaleron itself to improve the estimate. We clarify the amount of CP violation required for this scenario to explain the...

We study scenarios in which the baryon asymmetry is generated from the decay of a particle whose mass originates from the spontaneous breakdown of a symmetry. This is realized in many models, including low-scale leptogenesis and theories with classical scale invariance. Symmetry breaking in the early universe proceeds through a phase transition that gives the parent particle a time-dependent mass, which provides an additional departure from thermal equilibrium that could modi...

We study the cosmological evolution of asymmetries in the two-Higgs doublet extension of the Standard Model, prior to the electroweak phase transition. If Higgs flavour-exchanging interactions are sufficiently slow, then a relative asymmetry among the Higgs doublets corresponds to an effectively conserved quantum number. Since the magnitude of the Higgs couplings depends on the choice of basis in the Higgs doublet space, we attempt to formulate basis-independent out-of-equili...

The evolution of the electro-weak phase transition, including reheating due to the release of latent heat in shock waves, is calculated for various values of as yet unknown parameters of electro-weak theory such as latent heat and bubble wall surface tension. We show that baryon production, which occurs in the vicinity of the bubble walls of the phase transition, can be a sensitive function of bubble wall velocity, and this velocity dependence is important to include in the c...

If stable electroweak strings are copiously produced during the electroweak phase transition, they may contribute significantly to the presently observed baryon to entropy ratio of the universe. This analysis establishes the feasibility of implementing an electroweak baryogenesis scenario without a first order phase transition.

In this talk I briefly review the main ideas and challenges involved in the computation of the baryon asymmetry of the Universe. (Invited talk given at ``The Birth of the Universe and Fundamental Physics'', Rome, May 18--21, 1994.)

We argue that the creation of a baryon asymmetry in the early universe is an intriguing case where several aspects of ``Beyond'' physics are needed. We then concentrate on baryogenesis in a strong first-order phase transition and discuss that supersymmetric variants of the electroweak theory (MSSM and some version of NMSSM) rather naturally provide the necessary ingredients. The charginos and the stops play a prominent role. We present CP-violating dispersion relations in the...

After some introductory remarks about the prospects of first order phase transitions in the early universe, we discuss in some detail the electroweak phase transition. In the standard model case a clear picture is arising including perturbative and nonperturbative effects. Since in this case the phase transition is not strongly first order as needed for baryogenesis, we discuss supersymmetric variants of the standard model, the MSSM with a light stop$_R$ and a NMSSM model whe...