Heavy Wino-like Neutralino Dark Matter Annihilation into Antiparticles

TL;DR

This work analyzes indirect detection of heavy wino-like neutralino dark matter via cosmic-ray positrons and antiprotons, highlighting a non-perturbative electroweak enhancement of annihilation cross sections around $m\sim 2$ TeV that boosts observable fluxes. It models positron and antiproton production from $W^+W^-$ and $ZZ$ final states, and propagates the resulting spectra through the Galaxy using diffusion equations with resonant cross sections and halo-profile assumptions. The key finding is that the high-energy positron flux ($E \gtrsim 100$ GeV) from a $\sim 2$ TeV wino can exceed astrophysical backgrounds and could be detectable by PAMELA and AMS-02, with the positron channel being comparatively robust to diffusion uncertainties and potentially explaining the HEAT anomaly; the antiproton signal, while potentially comparable to background near the resonance, is more sensitive to astrophysical parameters and spectrum-slope uncertainties, making it harder to identify. Overall, a heavy wino-like neutralino around $m\sim 2$ TeV remains a compelling DM scenario with distinctive, testable indirect-detection signatures that could be probed by current and upcoming cosmic-ray experiments.

Abstract

The lightest neutralino is a viable dark matter (DM) candidate. In this paper we study indirect detection of the wino-like neutralino DM using positrons and antiprotons from the annihilation in the galactic halo. When the mass is around 2 TeV, which is favored from the thermal relic abundance, the non-perturbation effect significantly enhances the annihilation cross sections into positrons and antiprotons. We find that the positron and antiproton fluxes with energies larger than 100 GeV may become larger than the expected backgrounds. Since the positron flux is less sensitive to the astrophysical parameters, the detection may be promising in the upcoming experiments such as PAMELA and AMS-02. We also find the wino-like neutralino DM with mass around 2 TeV is compatible with the HEAT anomaly.

Figures (7)

• Figure 1: Cross sections, $\sigma v$, of the annihilation of the wino-like neutralinos into $W^+W^-$ (left figure) and $ZZ$ (right figure) in a non-relativistic limit. The mass difference between the wino-like neutralino and chargino is set to be 0.1 GeV. For comparison, the cross sections at the leading order in perturbation are shown as dashed lines. The bound state resonances appear around 2 TeV and 8 TeV.
• Figure 2: Fitting functions of the fragmentation functions $(dN_{e^+}/dx)_{WW}$ and $(dN_{e^+}/dx)_{ZZ}$ (solid lines) and HERWIG Monte-Carlo results in cases of $m = 0.2, 0.5, 1, 1.5$, and 2 TeV.
• Figure 3: (Interstellar) positron flux from the wino-like neutralino annihilation. The signal fluxes for the wino mass $m=0.3$, 0.6, 1, 1.5, 2, 2.5, and 3 TeV are shown as solid lines. The expected background flux of positrons from the cosmic ray simulation is also shown as a dotted line.
• Figure 4: (Left figure) Positron fraction, $e^+ /(e^+ +e^-)$, as a function of positron energy $E$ in the wino-like neutralino DM. For comparison, the expected background positron fraction, the positron data HEAT 94-95 and HEAT 2000 are also shown in this figure. (Right figure) Contour plot of the ratio between the positron fractions including positrons from the DM annihilation and without it (that is the background positron fraction) in a $(E,m)$ plane.
• Figure 5: Sensitivities of the upcoming experiments. The positron fraction, $e^+ /(e^+ +e^-)$, for $m = 2$ TeV and that of the background are shown as solid and dotted lines, respectively. The error bars in the figure correspond to the statistical errors projected for the PAMELA and AMS-02 experiments after three years of observations.