Implications of a light stop for the spontaneous CP breaking at finite temperature in a nonminimal supersymmetric standard model

We study the implications of a light stop for the spontaneous CP breaking at finite temperature in the Higgs sector of the Minimal Supersymmetric Standard Model with a gauge singlet. Assuming CP conservation at zero temperature, we show that the presence of a large mixing between the left- and the right-handed stops can trigger easily the spontaneous breaking of CP inside the bubbles nucleated during the electroweak phase transition. This allows to avoid the fine-tuning among the vacuum expectation values in the region of interest for the generation of the baryon asymmetry, namely the bubble walls, which has been recently analized.