Cosmic antiprotons as a probe for neutralino dark matter?

TL;DR

This work evaluates cosmic-ray antiprotons as an indirect probe of neutralino dark matter by computing the annihilation-induced flux within a wide MSSM parameter space and comparing it to a carefully modeled secondary antiproton background. It employs a diffusion-based propagation model with cylindrical geometry and includes solar modulation via a force-field treatment, exploring the dependence on halo profile and energy. A key finding is the existence of an optimal energy $T_{\rm opt}$ where the signal-to-background ratio is maximized, with some models peaking below $0.5$ GeV and others at $10$--$30$ GeV, yet no robust spectral feature distinguishes signal from background given current uncertainties. Overall, large astrophysical uncertainties prevent excluding MSSM models with current data, and the study highlights both the potential and the challenges of using antiprotons to probe neutralino dark matter, motivating searches at higher energies or under alternative halo assumptions.

Abstract

The flux of cosmic ray antiprotons from neutralino annihilations in the galactic halo is computed for a large sample of models in the Minimal Supersymmetric extension of the Standard Model. We also revisit the problem of estimating the background of low-energy cosmic ray induced secondary antiprotons, taking into account their subsequent interactions (and energy loss) and the presence of nuclei in the interstellar matter. We point out that in some cases the optimal kinetic energy to search for a signal from supersymmetric dark matter is above several GeV, rather than the traditional sub-GeV region. The large astrophysical uncertainties involved do not allow the exclusion of any of the MSSM models we consider, on the basis of current data.

Figures (3)

• Figure 1: a) The interstellar antiproton flux and the contribution from secondary and tertiary (i.e. $\bar{p}$s that have lost energy) antiprotons. The uncertainty due to the parametrization of the primary proton spectrum is also given as the shaded band. b) The same as the solid line in a) but solar modulated with $\phi_F=500$ MV. The Bess 95 and 97 data are also shown (Matsunaga et al., 1998; Orito, 1998).
• Figure 2: (a) The solar modulated antiproton fluxes at 0.35 GeV compared with Bess 97. The models have been coded according to their relic density, $\Omega_\chi h^2$. In (c) we show the flux of antiprotons from neutralino annihilation at the optimal kinetic energy, $T_{\rm opt}$, versus $T_{\rm opt}$. $T_{\rm opt}$ is defined as the energy at which $\Phi_{\rm signal}/\Phi_{\rm background}$ is highest and if the spectrum has more than one optimum, the highest two have been included in the plot. The models have been coded according to the neutralino mass in GeV. In (c) we show the antiproton spectra for 7 example models.
• Figure 3: An example of a composite spectrum consisting of our reference background $\bar{p}$ flux (Fig. \ref{['fig:back']} (b)) reduced by 24 % with the addition of the predicted flux from annihilating dark matter neutralinos of MSSM model number 5.