Higgsino dark matter in the MSSM

A cosmologically stable neutral component from a nearly pure $SU(2)$ doublet, with a mass $\sim 1.1\mathrm{TeV}$, is one appealing candidate for dark matter (DM) consistent with all direct dark matter searches. We explore this possibility in the context of the minimal supersymmetric extension of the Standard Model, with the Higgsino playing the role of DM, in theories where supersymmetry breaking is transmitted by gravitational interactions at the unification scale $M\simeq 2\times {10}^{16}\mathrm{GeV}$. We focus on the search for “light” supersymmetric spectra, which could be within reach of present and/or future colliders, in models with universal and nonuniversal Higgs and gaugino Majorana masses. The lightest supersymmetric particles of the spectrum are, by construction, two neutralinos and one chargino, almost degenerate, with a mass $\sim 1.1\mathrm{TeV}$, and a mass splitting of a few GeV. Depending on the particular scenario the gluino can be at its experimental lower mass bound $\sim 2.2\mathrm{TeV}$; in the squark sector, the lightest top squark can be as light as $\sim 1.6\mathrm{TeV}$, and the lightest slepton, the right-handed stau, can have a mass as light as 1.2 TeV. The lightest neutralino can be found in the next generation of direct dark matter experimental searches. In the most favorable situation, the gluino, with some specific decay channels, could be found during the next run of the LHC, and the lightest top squark during the high-luminosity LHC run.

Figure 1

Left: the shaded region is forbidden by the spin-independent cross section for ${\overline{\chi }}_1^0{\chi }_1^0$-proton in the plane $(M_1^0,M_2^0)$. Vertical (horizontal) dashed lines are mass values of ${\chi }_3^0$ (${\chi }_4^0$) in TeV. Dotted lines are $m_{{\chi }_2^0}-m_{{\chi }_1^0}$ in GeV. Right: plot of ${\sigma }_p^{\mathrm{SI}}$ (in pb) as a function of $M_1^0=M_2^0$ in TeV.

Figure 2

Mass spectra (in TeV) for neutralinos (left) and charginos (right) (solid lines) for $M_1^0=M_2^0$ and $\mu =1.1\mathrm{TeV}$. The mass differences $m_{{\chi }_2^0}-m_{{\chi }_1^0}$ (left) and $m_{{\chi }_1^{\pm }}-m_{{\chi }_1^0}$ (right) are in GeV.

Figure 3

Left: contour (dashed) lines of $A_t^0/\mu$ in the plane $(m_0/|\mu |,t_{\beta })$ satisfying the EoM (2.2) for universal gaugino masses. The shaded region is forbidden by the EWSB condition. Right: the same for contour (solid) lines of the lightest top squark running mass $m_{{\tilde{t}}_1}$ in TeV.

Figure 4

Left: contour (dashed) lines of $A_t^0/\mu$ in the plane $(m_0/|\mu |,t_{\beta })$ satisfying the EoM (2.2) for nonuniversal gaugino masses such that $M_{\tilde{g}}=2.2\mathrm{TeV}$. The shaded region is forbidden by the EWSB condition. Right: the same for contour (solid) lines of the lightest top squark running mass $m_{{\tilde{t}}_1}$ in TeV.

Figure 5

Left: contour (dashed) lines of $A_t^0/\mu$ in the plane $(m_0/|\mu |,m_H/|\mu |)$ for $t_{\beta }=10$ satisfying the EoM (2.2) for universal gaugino masses. The shaded region is forbidden by the EWSB condition. Right: the same for the contour (solid) lines of the lightest top squark running mass $m_{{\tilde{t}}_1}$ in TeV.

Figure 6

Left: contour (dashed) lines of $A_t^0/\mu$ in the plane $(m_0/|\mu |,m_H/|\mu |)$ for $t_{\beta }=10$ satisfying the EoM (2.2) for nonuniversal gaugino masses. The shaded region is forbidden by the EWSB condition. Right: the same for the contour (solid) lines of the lightest top squark running mass $m_{{\tilde{t}}_1}$ in TeV.