Natural SUSY with a bino- or wino-like LSP

In natural supersymmetry models, Higgsinos are always light because ${\mu }^2$ cannot be much larger than $M_Z^2$, while squarks and gluinos may be very heavy. Unless gluinos are discovered at LHC13, the commonly assumed unification of gaugino mass parameters will imply correspondingly heavy winos and binos, resulting in a Higgsino-like lightest supersymmetric particle (LSP) and small inter-Higgsino mass splittings. The small visible energy release in Higgsino decays makes their pair production difficult to detect at the LHC. Relaxing gaugino mass universality allows for relatively light winos and binos without violating LHC gluino mass bounds and without affecting naturalness. In the case where the bino mass $M_1\lesssim \mu$, then one obtains a mixed bino-Higgsino LSP with instead sizable ${\tilde{W}}_1-{\tilde{Z}}_1$ and ${\tilde{Z}}_2-{\tilde{Z}}_1$ mass gaps. The thermal neutralino abundance can match the measured dark matter density in contrast to models with a Higgsino-like LSP where weakly interacting massive particles are underproduced by factors of 10–15. If instead $M_2\lesssim \mu$, then one obtains a mixed wino-Higgsino LSP with large ${\tilde{Z}}_2-{\tilde{Z}}_1$ but small ${\tilde{W}}_1-{\tilde{Z}}_1$ mass gaps with still an underabundance of thermally produced weakly interacting massive particles. We discuss dark matter detection in other direct and indirect detection experiments and caution that the bounds from these must be interpreted with care. Finally, we show that LHC13 experiments should be able to probe these nonuniversal mass scenarios via a variety of channels including $\text{multilepton}+E_T^{\text{miss}}$ events, $WZ+E_T^{\text{miss}}$ events, $Wh+E_T^{\text{miss}}$ events, and $W^{\pm }{W}^{\pm }+E_T^{\text{miss}}$ events from electroweak chargino and neutralino production.

Figure 1

Variation in fine-tuning measure ${\mathrm{\Delta }}_{\mathrm{EW}}$ vs $M_1$ (red circles) or $M_2$ (blue pluses), with all other parameters fixed at their values for the RNS SUSY benchmark model point in Table 1. Here and in subsequent figures, the $M_i$ on the horizontal axis is the value of the corresponding gaugino mass parameter renormalized at the GUT scale. We cut the graphs off if the lighter chargino mass falls below 100 GeV.

Figure 2

Variation of electroweakino masses vs $M_1$ for a general RNS SUSY benchmark model with variable $M_1$ and $M_2=M_3$.

Figure 3

Variation of ${\mathrm{\Omega }}_{{\tilde{Z}}_1}^{\mathrm{TP}}{h}^2$ vs $M_1$ for a general RNS SUSY benchmark model with variable $M_1$ and $M_2=M_3$. The dashed line shows the measured value of the cold dark matter relic density.

Figure 4

Electroweakino pair production cross sections vs $M_1$ for the RNS SUSY benchmark model with variable $M_1$ but with $M_2=M_3$.

Figure 5

Chargino and neutralino production cross sections at a linear $e^{+}{e}^{-}$ collider with $\sqrt{s}=500\mathrm{GeV}$ with unpolarized beams for the RNS SUSY benchmark model with variable $M_1$ but with $M_2=M_3$.

Figure 6

Spin-independent $p{\tilde{Z}}_1$ scattering cross section vs $M_1$ (red dots) or $M_2$ (blue pluses) for the RNS benchmark point.

Figure 7

Spin-dependent $p{\tilde{Z}}_1$ scattering cross section vs $M_1$ (red circles) or $M_2$ (blue pluses) for the RNS benchmark point.

Figure 8

Thermally averaged neutralino annihilation cross section times velocity at $v=0$ vs $M_1$ (red dots) or $M_2$ (blue pluses) for the RNS benchmark point.

Figure 9

Variation of chargino and neutralino masses vs $M_2$ for the RNS SUSY benchmark model with variable $M_2$ but with $M_1=M_3$.

Figure 10

Variation of ${\mathrm{\Omega }}_{{\tilde{Z}}_1}^{\mathrm{TP}}{h}^2$ vs $M_2$ (blue curve) for the RNS SUSY benchmark model with variable $M_2$ but with $M_1=M_3$. We cut the graph off at the low end because $m_{{\tilde{W}}_1}$ falls below its LEP2 bound.

Figure 11

Electroweakino pair production cross sections vs $M_2$ for the RNS SUSY benchmark model with variable $M_2$ but with $M_1=M_3$.

Figure 12

Chargino and neutralino production cross sections with unpolarized electron and positron beams at a linear $e^{+}{e}^{-}$ collider with $\sqrt{s}=500\mathrm{GeV}$ for the RNS SUSY benchmark model with variable $M_2$ but with $M_1=M_3$.

Figure 13

Dominant component of the neutralino LSP in the $M_1$ vs $M_2$ plane for the RNS SUSY benchmark model. The LSP is dominantly a bino, wino, or Higgsino in the region denoted by blue dots, red pluses, and green crosses, respectively. Other parameters are fixed at their values for the RNSh model point in Table 1. In the region marked LEP2 excluded, $m_{{\tilde{W}}_1}<100\mathrm{GeV}$, whereas in the remaining unshaded region of the lower half-plane, $m_{{\tilde{W}}_1}<m_{{\tilde{Z}}_1}$.

Figure 14

The $m_{{\tilde{W}}_1}-m_{{\tilde{Z}}_1}$ mass gap in the $M_1$ vs $M_2$ plane for the RNS SUSY benchmark model.

Figure 15

The $m_{{\tilde{Z}}_2}-m_{{\tilde{Z}}_1}$ mass gap in the $M_1$ vs $M_2$ plane for the RNS SUSY benchmark model.

Figure 16

Thermally produced neutralino relic abundance in the $M_1$ vs $M_2$ plane for the RNS SUSY benchmark model.