Weak scale baryogenesis

We discuss a simple model for baryogenesis during the weak phase transition, which uses the anomalous baryon violation in the weak interactions. A departure from thermal equilibrium is provided if the transition is first order, and CP violation occurs in the neutrino couplings. Generating a sufficiently large baryon number requires that the τ neutrino is heavier than an MeV, or there must be a fourth family with all members heavier than 45 GeV.