04 November 2010

More Dark Matter Science

Scientists argue that they have found a gamma ray emission in the center of the galaxy consistent with a 7.3-9.2 GeV dark matter particle annihilating primarily to tau leptons distributed as mainstream dark matter theories expect it to be distributed, in a non-point source focused around the galactic center. Observations of dark matter phenomena are overwhelming, but the mechanism for this phenomena has been elusive and no directly observed particle or force has been able to fit the data.

The characteristics of the dark matter implied by these observations are consistent with theoretical expectations. In particular, the required dark matter distribution is in concordance with that predicted by numerical simulations, after accounting for a moderate degree of adiabatic contaction. Furthermore, the annihilation cross section required to normalize the signal is approximately equal to that of a simple thermal relic that freezes out with an abundance equal to the measured cosmological density of dark matter. Furthermore, we point out that the dark matter mass implied by this observation is remarkably similar to that needed to simultaneously explain the observations by the direct detection experiments CoGeNT and DAMA. In particular . . . the signals reported by the CoGeNT and DAMA collaborations can be consistently interpreted as elastically scattering dark matter particles with masses in the range of approximately 6.2 to 8.6 GeV.

In the dark matter scenario implied by the observations described in this paper, gamma rays are not the only potentially observable annihilation products. In particular, the electrons produced in the annihilations of dark matter (through either subsequent tau decays, or through annihilations directly to e+e and/or + ) will produce synchrotron emission peaking at frequences of syn 23 GHz (Ee=7 GeV)2 (B=100 G). Given the recently reported evidence of 100 microGauss-scale magnetic fields in the Inner Galaxy, it is not di cult to interpret the so-called WMAP haze as a signal of the dark matter particle described in this paper.

The results would seem to favor a light neutralino, a hypothetical type of particle in supersymmetry theory, as a dark matter candidate, and to disfavor other candidates for dark matters such as the axion, inert Higgs doublet, or sterile neutrino, none of which has an anticipated mass in the right range for these results. The expected mass is roughly the same as two bottom quarks, although they are poor dark matter candidates because they are highly unstable.

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