Antideuterons as a Signature of Supersymmetric Dark Matter

TL;DR

This paper argues that antideuterons offer a cleaner indirect signature of supersymmetric dark matter in the Galactic halo than antiprotons, because secondary production at low energy is strongly suppressed and solar modulation affects antiprotons more than antideuterons. It develops a coalescence-based production framework for antideuterons from both spallation and neutralino annihilation, coupling it to a two-zone diffusion model to predict the interstellar and Earth fluxes, including solar modulation. The results show that the secondary antideuteron flux is negligible below a few GeV/n, while neutralino-induced (primary) antideuterons yield a flat, low-energy spectrum, enhancing the SUSY/secondary ratio and making low-energy antideuterons a promising detection channel for AMS/ISSA. Across the MSSM parameter space, many configurations could produce 1–20 detectable low-energy antideuterons, providing a tangible pathway to test neutralino dark matter with cosmic-ray measurements.

Abstract

Once the energy spectrum of the secondary component is well understood, measurements of the antiproton cosmic-ray flux at the Earth will be a powerful way to indirectly probe for the existence of supersymmetric relics in the galactic halo. Unfortunately, it is still spoilt by considerable theoretical uncertainties. As shown in this work, searches for low-energy antideuterons appear in the mean time as a plausible alternative, worth being explored. Above a few GeV/n, a dozen spallation antideuterons should be collected by the future AMS experiment on board ISSA. For energies less than about 3 GeV/n, the antideuteron spallation component becomes negligible and may be supplanted by a potential supersymmetric signal. If a few low-energy antideuterons are discovered, this should be seriously taken as a clue for the existence of massive neutralinos in the Milky Way.

Figures (9)

• Figure 1: The IS secondary flux of antideuterons, expressed in units of $\rm m^{-2} \; s^{-1} \; sr^{-1} \; GeV^{-1}$, is presented as a function of kinetic energy per nucleon. The solid curve corresponds to the median value of the cosmic--ray proton spectrum, as derived by Bottino et al. [4]. The dashed and dotted lines respectively stand for the maximal and minimal values of the primary proton flux from which the antideuterons originate.
• Figure 2: The median IS spectrum of Fig. \ref{['fig:dbar_sec_is']} (solid curve) has been modulated at solar maximum (dashed line) and minimum (dotted line).
• Figure 3: The IS flux of secondary antideuterons (heavier solid curve) decreases at low energy whereas the energy spectrum of the antideuterons from supersymmetric origin tends to flatten. The four cases of table \ref{['table:susy']} are respectively featured by the solid (a), dotted (b), dashed (c) and dot-dashed (d) curves.
• Figure 4: Same as in Fig. \ref{['fig:dbar_prim_is']} but modulated at solar maximum ( left) and minimum ( right).
• Figure 5: The supersymmetric--to--secondary IS flux ratio for antiprotons (lower curves) and antideuterons (upper curves) is presented as a function of the kinetic energy per nucleon. The supersymmetric configurations are those reported in table \ref{['table:susy']} and featured in Figs. \ref{['fig:dbar_prim_is']} and \ref{['fig:dbar_prim_solmod']}. Below a few GeV/n, the flux ratio is always larger for $\bar{\rm D}$'s than for $\bar{\rm p}$'s. For the supersymmetric configurations of table \ref{['table:susy']}, the antiproton signal is swamped into its background. This is not the case for antideuterons. At low energy, the flux of primaries is several orders of magnitude above the $\bar{\rm D}$ background.