Constraining supersymmetric dark matter with synchrotron measurements

The annihilations of neutralino dark matter (or other dark matter candidate) generate, among other standard model states, electrons and positrons. These particles emit synchrotron photons as a result of their interaction with the galactic magnetic field. In this paper, we use the measurements of the Wilkinson Microwave Anisotropy Probe satellite to constrain the intensity of this synchrotron emission and, in turn, the annihilation cross section of the lightest neutralino. We find this constraint to be more stringent than that provided by any other current indirect detection channel. In particular, the neutralino annihilation cross section must be less than $\approx 3\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$ ($1\times {10}^{25}{\mathrm{cm}}^3/\mathrm{s}$) for 100 GeV (500 GeV) neutralinos distributed with a Navarro-Frenk-White halo profile. For the conservative case of an entirely flat dark matter distribution within the inner 8 kiloparsecs of the Milky Way, the constraint is approximately a factor of 30 less stringent. Even in this conservative case, synchrotron measurements strongly constrain, for example, the possibility of wino or Higgsino neutralino dark matter produced nonthermally in the early universe.