Does LEP prefer the NMSSM?

TL;DR

Addressing whether LEP data prefer the NMSSM over the MSSM, the paper analyzes naturalness and electroweak baryogenesis in the NMSSM. It shows that the extra $λ$ coupling lifts the lightest Higgs mass at low $tanβ$ via the tree-level contribution, reducing fine-tuning relative to the MSSM. It demonstrates that the NMSSM supports a strongly first-order electroweak phase transition through a tree-level cubic term, enabling electroweak baryogenesis within LEP constraints. By solving the μ problem with $λ N H_1 H_2$ and exploiting the extended Higgs sector, the NMSSM offers a coherent solution to Higgs mass limits, naturalness, and baryogenesis, with potential relevance for nearby models.

Abstract

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 \tanβregion of the minimal supersymmetric standard model (MSSM). We show that the low \tan βregion of the NMSSM is clearly favoured over the MSSM with regard to the physical Higgs boson mass, fine-tuning, and electroweak baryogenesis.

Figures (3)

• Figure 1: The maximum sensitivity parameter $\Delta^{max}$ as a function of the lightest physical Higgs mass for $tan\beta=2$. We have fixed $m_0=100$ GeV, $A_t(0)=0$ GeV, $M_2(0)=M_1(0)=500$ GeV and $\mu <0$ ($\lambda x <0$), while varying $M_3(0)$, $m_{H_1}(0)$ and $m_{H_2}(0)$. The darkest grey region correspond to the NMSSM, and the lighter grey region to the MSSM. The thin dotted line at 108 GeV, and the lightest shaded region to the left of it, represents the LEP excluded region on the standard model Higgs boson mass.
• Figure 2: Same as in Fig. (1) for $\tan\beta=3$.
• Figure 3: Same as in Fig. (1) for $\tan\beta=5$.