Neutrinos for TeV neutralinos

One of the most well-founded candidates for dark matter remains a split-supersymmetry (SUSY) model with a Higgsino- or winolike lightest superpartner and the grander SUSY model providing answers for the hierarchy problem and grand unified theory scale unification. The relatively heavy scalar superpartners imply such models would not yet be seen at collider experiments, and mixing-suppressed couplings place such models outside the reach of current direct detection experiments. As such particles annihilate fairly readily to electroweak bosons, a significant neutrino signal can arise near the Galactic Center that may be visible to dedicated searches at current and future neutrino telescopes.

Figure 1

Total exposure for $2\sigma$ exclusion of thermally produced Higgsino DM as a function of the radius of the cone of interest about the GC. The bands denote the range of backgrounds from solely astrophysical neutrinos (lower end) to atmospheric and astrophysical neutrinos (upper end). For cascades (lower, green band), both electron and $\tau$ neutrinos are included for both the signal and background, while for tracks (upper, blue band) only muon neutrinos are used. The TeV-scale angular resolution of IceCube is shown in vertical dashed lines for track and cascade signatures in the detector.

Figure 2

Sensitivity using tracks (blue) or cascade (green) neutrino signatures in IceCube for a search for Higgsino-like DM with some additional physics allowing it to compose the entire observed DM abundance. For tracks, only ${\nu }_{\mu }$ signal and background are possible, while for cascades only electron and $\tau$ neutrinos are included due to the large atmospheric ${\nu }_{\mu }$ background. Sensitivities are shown as bands based on a range of possible projections of background neutrino flux.

Figure 3

Neutrino flux for (black) wino- and (gray) Higgsino-like neutralino DM shown as differential flux multiplied by the energy squared. Masses are set by the requirement that the neutralino produces the full DM relic abundance through thermal production, so the winolike neutralino mass is 2.8 TeV (black) while for a Higgsino-like neutralino it is 1.1 TeV (gray). The combined ${\nu }_{\mathrm{e}}+{\nu }_{\tau }$ signal is shown, although the spectra for different $\nu$ flavors are not visibly distinct beyond a small suppression of ${\nu }_{\tau }$. The astrophysical ${\nu }_{\mathrm{e}}+{\nu }_{\tau }$ background (solid red) follows the power law described in Ref. [51], while atmospheric neutrino spectra both for ${\nu }_{\mathrm{e}}+{\nu }_{\tau }$ (dashed red) and all $\nu$ flavors combined (dotted red) follow the Honda model [53].

Figure 4

Comparison of IceCube (dark blue), IceCube Gen2 (light blue), and KM3NeT (green) sensitivities to neutralino DM. These are shown as IceCube (left), KM3NeT (right), and a focus on the region of interest for wino exclusion with future experiments directly compared in the optimistic background assumption (below). The bands for each detector range from the most conservative case at the top, detecting only electron and $\tau$ neutrinos with both astrophysical and atmospheric backgrounds, to the most optimistic case at the bottom, detecting all neutrino flavors with only astrophysical neutrino backgrounds. The horizontal bands assume the neutralinos saturate the measured DM abundance while the diagonal bands are sensitivities assuming thermal production of Higgsinos (unfilled) and winos (filled). For readability in the thermal Higgsino case, we show only the most conservative scenario for IceCube and the most optimistic scenario for IceCube Gen2, encompassing the range of possibilities. The theoretically expected annihilation cross section is shown for Higgsinos (orange) and winos (red).