New fermions, strongly coupled to the Standard Model Higgs boson, provide a well motivated extension of the Standard Model (SM). In this work we show that, once new physics at heavier scales is added to stabilize the Higgs potential, such an extension of the SM can strengthen the first order electroweak phase transition and make the electroweak baryogenesis mechanism feasible. We propose a SM extension with TeV Higgsinos, Winos and Binos that satisfy the following properties: a) The electroweak phase transition is strong enough to avoid sphaleron erasure in the broken phase for values of the Higgs mass m H < ∼ 300 GeV; b) It provides large CP-violating currents that lead to the observed baryon asymmetry of the Universe for natural values of the CP-violating phase; c) It also provides a natural Dark Matter candidate that can reproduce the observed dark matter density; d) It is consistent with electroweak precision measurements; e) It may arise from a softly broken supersymmetric theory with an extra (asymptotically free) gauge sector; f ) It may be tested by electron electric dipole moment experiments in the near future.
We study the velocity of bubble walls in the electroweak phase transition. For several extensions of the Standard Model, we estimate the friction and calculate the wall velocity, taking into account the hydrodynamics. We find that deflagrations are generally more likely than detonations. Nevertheless, for models with extra bosons, which give a strongly first-order phase transition, the deflagration velocity is in general quite high, 0.1 v w 0.6. Therefore, such phase transitions may produce an important signal of gravitational waves. On the other hand, models with extra fermions which are strongly coupled to the Higgs boson may provide a strongly first-order phase transition and small velocities, 10 −2 v w 10 −1 , as required by electroweak baryogenesis.
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