Baryogenesis from an Earlier Phase Transition

We explore the possibility that the observed baryon asymmetry of the universe is the result of an earlier phase transition in which an extended gauge sector breaks down into the $SU(3)_C \times SU(2)_L \times U(1)_Y$ of the Standard Model. Our proto-typical example is the Topflavor model, in which there is a separate $SU(2)_1$ for the third generation from the $SU(2)_2$ felt by the first two generations. We show that the breakdown of $SU(2)_1 \times SU(2)_2 \to SU(2)_L$ results in lepton number being asymmetrically distributed through-out the three families, and provided the SM electroweak phase transition is {\em not} strongly first order, results in a non-zero baryon number, which for parameter choices that can be explored at the LHC, may explain the observed baryon asymmetry.