Electroweak Baryogenesis and Dark Matter in the nMSSM

TL;DR

The paper investigates whether the nMSSM, a minimal singlet-extended MSSM, can accommodate both electroweak baryogenesis and a viable dark matter candidate. It analyzes the zero- and finite-temperature Higgs and neutralino sectors, derives the finite-temperature effective potential, and performs a numerical scan under LEP and perturbativity constraints. The authors demonstrate that a strongly first-order electroweak phase transition is achievable due to a tree-level cubic term, and that the LSP neutralino typically lies in the $m_{ ilde{N}_1} oughly 30$–$40$ GeV range with a substantial singlino component, yielding a relic density compatible with observations. The model predicts a light Higgs spectrum below $ oughly 250$ GeV with possible invisible decays to neutralinos, offering distinctive collider signatures and a concrete weak-scale connection between baryogenesis and dark matter.

Abstract

We examine the possibility of electroweak baryogenesis and dark matter in the nMSSM, a minimal extension of the MSSM with a singlet field. This extension avoids the usual domain wall problem of the NMSSM, and also appears as the low energy theory in models of dynamical electroweak symmetry breaking with a so-called fat-Higgs boson. We demonstrate that a strong, first order electroweak phase transition, necessary for electroweak baryogenesis, may arise in regions of parameter space where the lightest neutralino provides an acceptable dark matter candidate. We investigate the parameter space in which these two properties are fulfilled and discuss the resulting phenomenology. In particular, we show that there are always two light CP-even and one light CP-odd Higgs bosons with masses smaller than about 250 GeV. Moreover, in order to obtain a realistic relic density, the lightest neutralino mass tends to be smaller than $M_Z/2$, in which case the lightest Higgs boson decays predominantly into neutralinos.

Figures (8)

• Figure 1: Allowed regions in the $\tan\beta-\lambda$ plane. The region consistent with perturbative unification lies below the thick solid line, while the regions consistent with the LEP II constraints (and $m_{\tilde{N}_1}>25$ GeV) lie above the thinner lines. Among these, the solid line corresponds to a gaugino phase of $\phi = \pi$, while the dotted and dashed lines correspond to $\phi = 0,\:\:\pi/2$ respectively.
• Figure 2: Allowed regions in the $|\mu|-|M_2|$ plane for a gaugino phase of $\phi = 0,\:\pi/2,\:\pi$, and $(\tan\beta,\lambda)$ below the perturbativity bound. The allowed region lies in the central area. Recall that $\mu = -\lambda\,v_s$ in the model.
• Figure 3: Mass of the lightest neutralino. The region to the right of the solid line is consistent with the LEP II constraints listed above. The region surrounded by the dotted line is also consistent with perturbative unification.
• Figure 4: Values of $D$ for parameter sets leading to a strongly first order phase transition for: (a) $\lambda$ below the perturbative bound; (b) general values of $\lambda$ in the range $0.7<\lambda<2.0$. The region consistent with the experimental constraints lies within the area enclosed by the solid lines.
• Figure 5: Neutralino relic density as a function of mass for two values of the mixing parameter, $\left||{N}_{13}|^2 -|{N}_{14}|^2\right| = 0.1\,\hbox{(dotted)}, \:0.5\,\hbox{(dashed)}$ and typical values of the Higgs mixing parameters. The region to the right of the thick solid line is consistent with the observed $Z$ width. The scattered points correspond to parameter sets that give a strong first order phase transition, and are consistent with perturbative unification.