Decaying dark matter as a probe of unification and TeV spectroscopy

In supersymmetric unified theories the dark matter particle can decay, just like the proton, through grand unified interactions with a lifetime of order of $\sim {10}^{26}\sec$. Its decay products can be detected by several experiments—including Fermi, HESS, PAMELA, ATIC, and IceCube—opening our first direct window to physics at the TeV scale and simultaneously at the unification scale $\sim {10}^{16}\mathrm{GeV}$. We consider possibilities for explaining the electron/positron spectra observed by HESS, PAMELA, and ATIC, and the resulting predictions for the gamma-ray, electron/positron, and neutrino spectra as will be measured, for example, by Fermi and IceCube. The discovery of an isotropic, hard gamma ray spectral feature at Fermi would be strong evidence for dark matter and would disfavor astrophysical sources such as pulsars. Substructure in the cosmic ray spectra probes the spectroscopy of new TeV-mass particles. For example, a preponderance of electrons in the final state can result from the lightness of selectrons relative to squarks. Decaying dark matter acts as a sparticle injector with an energy reach potentially higher than the LHC. The resulting cosmic ray flux depends only on the values of the weak and unification scales.

Figure 1

The $\mathrm{\text{electron}}+\mathrm{\text{positron}}$ spectrum produced by the decay of dark matter ($s$ or $\tilde{s}$) to smuon pairs (solid black line) and tau-stau pairs (dot-dashed red line) as discussed in the text. The HESS and ATIC data is shown by red squares and blus circles, respectively. The systematic error of HESS is shown as a grey band and its superimposed energy uncertainty is shown as a lighter grey band. The background and smuon signal components of the flux are shown by dotted lines.

Figure 2

The “multi feature” $\mathrm{\text{electron}}+\mathrm{\text{positron}}$ spectra produced in simple dark matter decays scenarios. The short-dashed purple line is an example of multiple features arising from decays into leptons and sleptons. The blue dotted line is an example of a flavor universal decay to two sleptons of different masses. The long-dashed green line is for two DM components decaying to muons and smuons. The experimental data shown is similar to that in Fig. 1. The two signal components and the background in the slepton case, as well as the background are shown as dotted lines.

Figure 3

The positron fraction produced by some of scenarios discussed in the text—decays to smuons (Scenario 1, solid black line), a universal lepton-slepton decay (Scenario 2, short-dashed purple line) and decays to sleptons (Scenario 2, dotted black line). The background positron fraction from two propagation models is shown in gray, thin dotted lines. The PAMELA data is shown (black circles).

Figure 4

The gamma-ray spectra from final state radiation and $\tau$ decay. The solid (black) and dot-dashed (red) lines are as in Fig. 1. The dashed (green) and dotted (blue) lines are as in Fig. 2. Only the signals are plotted, not signal plus background. Gray is the expected background from 42. These are shown at a galactic latitude $b=60°$ and longitude $l=0°$.

Figure 5

The average ${\nu }_{\mu }$ flux produced from a Dark Matter particle decay in different examples. The solid (black) and dot-dashed (red) lines are as in Fig. 1. The dotted (blue) line is as in Fig. 2. AMANDA data is shown in gray [16]. The bin size is taken to be 0.2 in ${\mathrm{Log}}_{10}(\frac{E}{\mathrm{GeV}})$, as it appears in 16.