Attractive features of Higgsino Dark Matter in the Next-to-Minimal Supersymmetric Standard Model

TL;DR

This work shows that in the General NMSSM, Higgsino-dominated dark matter can satisfy the observed relic density with masses well below the MSSM benchmark, thanks to substantial Higgsino–Singlino mixing. The authors derive analytic expressions for the mixing effects on both the mass spectrum and DM-nucleon interactions, and perform extensive numerical scans incorporating the latest LZ (2024) constraints and Higgs data. They find viable regions with $m_{ ilde\chi^0_1}$ around a few hundred GeV up to about $1~\rm TeV$, with SI scattering rates that can be suppressed through cancellations among Higgs states, and SD rates further reduced by mixing. The results highlight that the GNMS framework opens a richer parameter space for Higgsino DM than the MSSM, with distinct experimental signatures accessible to HL-LHC, DARWIN, CTA, and IceCube-Gen2 in the near future.

Abstract

In the Higgsino dark matter (DM) scenario of the Minimal Supersymmetric Model (MSSM), the mixing of Gaugino and Higgsino influences the mass splitting between neutralinos predominantly composed of Higgsino and introduces coupling between the DM and Higgs bosons. These effects modify the DM-nucleon scattering cross-section, causing conflicts with the latest direct detection results from LZ experiments for both substantial and minute mixings. Consequently, the experimental measurement of DM relic density necessitates the Higgsino DM mass to be approximately 1.1 TeV. We discovered that in the Higgsino DM scenario of the Next-to-Minimal Supersymmetric Model (NMSSM), the mixing of Higgsino and Singlino introduces analogous effects, with a crucial distinction being that the current LZ experiment permits significant mixing between Singlino and Higgsino. This pronounced mixing effect effectively attenuates the interactions between Higgsino-dominated neutralinos and standard model particles, enabling DM masses exceeding roughly 670 GeV to achieve the correct relic abundance. Through analytical formulas and numerical results, we elucidated these characteristics which were not observed before. Our research reveals that in the NMSSM, when comprehensively examining the mixing effects of Higgsino, Gaugino, and Singlino, the properties of Higgsino DM become markedly more intricate compared to the MSSM predictions.

Figures (4)

• Figure 1: Two-dimensional profile likelihoods of the function $\cal{L}$ in Eq. (\ref{['Likelihood']}), projected onto the $|m_{\tilde{\chi}_1^0}|-\lambda$, $|m_{\tilde{\chi}_1^0}|-d^\prime$, $|m_{\tilde{\chi}_1^0}|-N_{15}$, and $|m_{\tilde{\chi}_1^0}|-\Delta m$ planes, respectively. Here, $N_{15} \simeq \sin \theta$ represents the fraction of Singlino component in the Higgsino-dominated DM, and $\Delta m \equiv m_{\tilde{\chi}_1^{\pm}}- |m_{\tilde{\chi}_1^0}|$ denotes the mass splittings between $\tilde{\chi}_1^\pm$ and $\tilde{\chi}_1^0$. Since the best point (marked with pin symbol) yields $\chi^2 \simeq 0$, the boundaries for $1 \sigma$ and $2 \sigma$ confidence intervals correspond to $\chi^2 \simeq 2.3$ and $\chi^2 \simeq 6.18$, respectively, indicated by white and red solid lines. This figure illustrates how the DM relic abundance constrains the parameter space of the GNMSSM. In generating this figure, we have applied constraints from the 2022 LZ results LZ:2022lsv and the latest Higgs data fitting procedures described in Ref. LZ:2022lsv, as detailed in the preceding text.
• Figure 3: Profile likelihood maps of $\cal{L}$, projected onto the $|m_{\tilde{\chi}_1^0}|-\lambda$ planes (upper panels) and the $|m_{\tilde{\chi}_1^0}|-V_h^S$ planes. In obtaining this figure, we updated the samples in Fig. \ref{['Fig1']} by including the constraints from the 2024 LZ results.
• Figure 4: Profile likelihoods of $\sigma^{\rm SD}_n$ and $\sigma^{\rm SI}_{\rm eff}$ as functions the DM mass. All displayed points satisfy the complete set of updated experimental constraints, reflecting current status of DM interactions with nucleon in the GNMSSM.
• Figure 6: Same as Fig. \ref{['Fig5']}, but for the dependence of relic abundance on the gaugino mass.