Dark matter in the finely tuned minimal supersymmetric standard model

We explore dark matter in the finely-tuned minimal supersymmetric standard model (MSSM) recently proposed by Arkani-Hamed and Dimopoulos. Relative to the MSSM, there are fewer particles at freeze-out, so the calculation of the relic abundance simplifies. Similarly, the predictions for direct detection of the dark matter sharpen. There is a large region of mixed bino—higgsino dark matter where the lightest supersymmetric particle will be accessible at both the LHC and future direct detection experiments, allowing for a conclusive identification of the dark matter particle. Typical dark matter-nucleon cross sections are ${10}^{-45}-{10}^{-44}{\mathrm{c}\mathrm{m}}^2$. This model also possesses a novel region where the dark matter annihilates via an $s$-channel Higgs boson resonance.

Figure 1

Points in the $\mu -M_1$ plane that satisfy the relic abundance constraint from WMAP. The region at low $M_1$ extending to large $\mu$ is the Higgs resonance region; the dark matter can be very nearly bino in this region. The diagonal line represents a mixed bino-higgsino dark matter region. The allowed region is shown for various values of $\tan \beta$, scalars masses, $m_S$, and $r\equiv M_2/M_1$. The top-quark mass is set to 178 GeV.

Figure 2

The spin-independent LSP-nucleon scattering cross section for point agreeing with the WMAP relic density constraint. Curves are plotted for various values of $m_S$ (the scale of the scalar masses), $\tan \beta$ (set at $m_S$), and $r\equiv M_2/M_1$. The flat regions for $m_{\chi }\gtrsim 80\mathrm{G}\mathrm{e}\mathrm{V}$ correspond to mixed bino-higgsino dark matter. The sharp decrease at lower masses is due to resonant annihilation through the Higgs boson and $Z$-boson poles. Also shown are the current bound from the results of the CDMS at Soudan [16], the projected bounds from this experiment [17], and projected bounds from a representative next generation dark matter experiment, GENIUS [18].