High-energetic Cosmic Antiprotons from Kaluza-Klein Dark Matter

TL;DR

The paper investigates the high-energy antiproton flux from annihilations of Kaluza-Klein dark matter, specifically the LKP $B^{(1)}$, in the Milky Way. It derives the particle-physics source term $Q_{ar p}(T,\mathbf r)$ and uses a two-zone diffusion framework to propagate antiprotons, exploring how different halo profiles (NFW, Moore, isothermal) and the presence of dark-matter clumps affect the signal. The main finding is that, under standard smooth-halo assumptions, the antiproton signal is subdominant to the secondary background, but substantial boosts from clumpy halos can produce a detectable high-energy distortion in the 10–100 GeV window, accessible to PAMELA and especially AMS-02. The work emphasizes that such signatures, together with potential positron signals, could help distinguish KK dark matter from neutralinos and motivate future observational tests, while noting significant astrophysical uncertainties and constraints from existing data on low-energy antiprotons.

Abstract

The lightest Kaluza-Klein particle (LKP) in models with universal extra dimensions is an interesting dark matter candidate that has recently received great attention. Here, we investigate the antiproton flux from LKP annihilations in the galactic halo. In our analysis we include different halo density profiles and allow for part of the dark matter to be concentrated in 'clumps' rather than being distributed homogeneously. After re-analyzing the observational bounds on the allowed amount of clumpiness, we find that LKP annihilations may well give a significant contribution to the antiproton flux at energies higher than about 10 GeV, while for energies above around 500 GeV the conventional background is expected to dominate again. The shortly upcoming PAMELA satellite will already be able to measure part of this high-energy window, while planned experiments like AMS-02 will have access to the full energy range of interest.

Figures (5)

• Figure 1: The differential antiproton spectrum per $B^{(1)}$ pair annihilation event. From bottom to top, the plots correspond to an LKP mass of $m_{B^{(1)}}=500$, 800 and 1000 GeV, respectively.
• Figure 2: The antiproton background flux as determined in maub, extrapolated for the energy range from 100 GeV to 1 TeV, is shown together with the data taken by the balloon-borne experiments BESS bess and CAPRICE caprice. The dashed lines show the contribution from LKP annihilations, with an LKP mass of $m_{B^{(1)}}=800$ GeV and, from bottom to top, an isothermal, NFW and Moore halo profile, respectively.
• Figure 3: The same as Fig. \ref{['flux_profiles']}, now for an NFW profile and, from left to right, LKP masses $m_{B^{(1)}}=500$, 800 and 1000 GeV.
• Figure 4: The solid line shows the expected antiproton spectrum for the case of a clumpy NFW profile with $f\delta=200$ and $m_{B^{(1)}}=800$ GeV; the dotted and dashed lines give, respectively, the background flux and the contribution from LKP annihilations alone. The data points are the same as those of Fig. \ref{['flux_profiles']}; in addition, the detectional prospects of PAMELA pamela and AMS-02 ams are indicated by displaying their projected data after three years of operation (only statistical errors are included; error bars smaller than the symbol size are not shown). For AMS-02, only energies above 100 GeV are considered.
• Figure 5: The same as in Fig. \ref{['flux_clump800']}, but now for $f\delta=$1000 and a hypothetical dark matter candidate with mass 7 TeV that was recently proposed to explain the observed gamma ray signal from the galactic center BBEGa.