Résumé
We study the naturalness of electroweak symmetry breaking and baryogenesis in the next-to-minimal supersymmetric standard model (NMSSM). Our study is motivated by the recent LEP bounds on the Higgs boson mass which severely constrains the low tan
β region of the minimal supersymmetric standard model (MSSM). We show that the low tan
β region of the NMSSM is clearly favoured over the MSSM with regard to the physical Higgs boson mass, fine-tuning, and electroweak baryogenesis.