Does LEP prefer the NMSSM?

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 beta region of the minimal supersymmetric standard model (MSSM). We show that the low tan beta region of the NMSSM is clearly favoured over the MSSM with regard to the physical Higgs boson mass, fine-tuning, and electroweak baryogenesis. (C) 2000 Elsevier Science B.V. All rights reserved.