Kaluza-Klein Dark Matter and Galactic Antiprotons

TL;DR

The study investigates whether Kaluza-Klein dark matter (KKDM), in particular the LKP $B^{(1)}$ and the warped-space LZP, could be detected indirectly via antiprotons produced in the Galactic halo. It develops the primary antiproton source term from LKP annihilations and propagates the resulting flux through a diffusion–convection model constrained by cosmic-ray data, comparing predictions to the secondary background and exploring halo-density profiles. The results show that, due to large propagation uncertainties and moderate sensitivity to central cusps, antiprotons are generally not a robust signature for KKDM, though under optimistic diffusion and halo assumptions they can constrain low-mass scenarios (e.g., certain $M_{ m LKP}$ or $M_{ m LZP}$ values) and could become detectable with future data from AMS-02. The work highlights the critical role of Galactic propagation uncertainties in indirect detection and motivates complementary probes (positrons, gamma rays) and improved propagation constraints to sharpen KKDM tests.

Abstract

Extra dimensions offer new ways to address long-standing problems in beyond the standard model particle physics. In some classes of extra-dimensional models, the lightest Kaluza-Klein particle is a viable dark matter candidate. In this work, we study indirect detection of Kaluza-Klein dark matter via its annihilation into antiprotons. We use a sophisticated galactic cosmic ray diffusion model whose parameters are fully constrained by an extensive set of experimental data. We discuss how fluxes of cosmic antiprotons can be used to exclude low Kaluza-Klein masses.

Figures (7)

• Figure 1: The primary interstellar antiproton flux is featured as a function of the antiproton kinetic energy $T_{\bar{p}}^{\rm IS}$ for a LKP mass of 300 GeV and 1 TeV. Maximal values for the diffusion parameters have been assumed here -- see Tab. \ref{['table:prop']}. The three different halo profiles that have been selected in this calculation are described in Tab. \ref{['tab:indices']}. The IS secondary component is the solid black line that overcomes the primary fluxes.
• Figure 2: The same as before but with median diffusion parameters. Primary fluxes drop by one order of magnitude.
• Figure 3: The same as before but with minimum diffusion parameters. Fluxes have decreased by two orders of magnitude with respect to the maximal case. Cosmic rays no longer come from the galactic center. As a consequence, the primary component is insensitive to the sharpness of the central cusp and the three different halo profiles that have been chosen in this calculation -- isothermal, NFW and Moore -- lead to the same spectra.
• Figure 4: The primary antiproton fluxes correspond to the warped geometry of Agashe1Agashe2. The LZP mass has been varied from 30 to 70 GeV with a Kaluza-Klein scale $M_{\rm KK}$ of 3 TeV. When the LZP mass is close to $M_{\rm Z^{0}} / 2$, the annihilation becomes resonant and the primary signal exceeds the conventional background of secondary antiprotons that lies in the narrow band within the two solid black lines. Maximal diffusion parameters have been assumed for the LZP antiproton spectra with a canonical isothermal DM distribution.
• Figure 5: When the diffusion parameters are varied over the entire domain that is compatible with the B/C ratio, antiproton primary fluxes span two orders of magnitude whilst the secondary component lies within a much narrower band. The case of a resonant LZP has been featured here with $M_{\rm LZP} = 40$ -- blue dashed -- and 50 GeV -- solid magenta. A canonical isothermal DM distribution has been assumed. In the case of minimal diffusion, the LZP signal is well below the background.