Z'-ino-driven Electroweak Baryogenesis in the UMSSM

The viable window to electroweak baryogenesis in a supersymmetric $U(1)'$ model is studied in light of the 126 GeV Higgs boson. To investigate the decoupling of the sphaleron process in the broken phase, we evaluate the sphaleron rate and order of the electroweak phase transition. In this model, the electroweak phase transition is strongly first order due to the doublet-singlet Higgs mixing. Consequently, for typical parameter sets the $Z'$ boson has to be lighter than (150-300) GeV and thus leptophobic to be consistent with the collider bounds. We also estimate the baryon asymmetry of the universe based on the closed-time-path formalism, and find that the CP-violating source term fueled by the $Z'$-ino can generate sufficient baryon asymmetry.