Electroweak baryogenesis in the presence of an isosinglet quark

We consider the possibility of electroweak baryogenesis in a simple extension of the standard model with an extra singlet complex scalar and a vector-like down quark. We show that in the present model the first-order electroweak phase transition can be strong enough to avoid the baryon asymmetry washout by sphalerons and that the CP-violating effects could in principle be sufficient to explain the observed baryon-to-entropy ratio nB/s∼10−10. Other appealing features of the model include the generation of a CKM phase from spontaneous CP breaking at a high energy scale and a possible solution of the strong CP problem through the natural suppression of the parameter θ̄.