WMAP Microwave Emission Interpreted as Dark Matter Annihilation in the Inner Galaxy

TL;DR

The paper tests whether the WMAP haze can be explained by synchrotron emission from ultra-relativistic $e^+$/$e^-$ produced by dark matter annihilation in the inner Galaxy. It develops a self-consistent diffusion-loss model for a $100\,\mathrm{GeV}$ neutralino with $\langle\sigma_A v\rangle=2\times10^{-26}\ \mathrm{cm^3\,s^{-1}}$ within a truncated NFW halo, predicting the resulting electron distribution and radio synchrotron output. The results show that about 25% of annihilation power could appear as synchrotron emission, with spectral and morphological properties broadly consistent with the WMAP haze and with accompanying inverse-Compton $\gamma$-ray expectations, though substantial uncertainties remain. The work proposes cross-checks with X-ray and $\gamma$-ray data, as well as observations of other galaxies or dwarfs, to test the DM interpretation and guide future accelerator searches for concordant particle physics.

Abstract

Excess microwave emission observed in the inner Galaxy (inner ~1 kpc) is consistent with synchrotron emission from highly relativistic electron-positron pairs produced by dark matter particle annihilation. More conventional sources for this emission, such as free-free (thermal bremsstrahlung), thermal dust, spinning dust, and the softer Galactic synchrotron traced by low-frequency surveys, have been ruled out. The total power observed in the range 23 < nu < 61 GHz is between 10^{36} and 5x10^{36} erg/s, depending on the method of extrapolation to the Galactic center, where bright foreground emission obscures the signal. The inferred electron energy distribution is diffusion hardened, and is in qualitative agreement with the energy distribution required to explain the gamma ray excess in the inner Galaxy at 1-30 GeV as inverse-Compton scattered starlight. We investigate the possibility that this population of electrons is produced by dark matter annihilation of 100 GeV particles, with cross section <sigma v>=2x10^{-26} cm^3/s, and an 1/r dark matter mass profile truncated in the inner Galaxy, and find this scenario to be consistent with current data.