A Radio Astronomy Search for Cold Dark Matter Axions
  The search for axions has gained ground in recent years, with laboratory
searches for cold dark matter (CDM) axions, relativistic solar axions and
ultra-light axions the subject of extensive literature. In particular, the
interest in axions as a CDM candidate has been motivated by its potential to
account for all of the inferred value of $\Omega_{DM} \sim 0.26$ in the
standard $\Lambda CDM$ model. Indeed, the value of $\Omega_{DM} \sim 0.26$
could be provided by a light axion. We investigate the possibility of
complementing existing axion search experiments with radio telescope
observations in an attempt to detect axion conversion in astrophysical magnetic
fields. Searching for a CDM axion signal from a large-scale astrophysical
environment provides new challenges, with the magnetic field structure playing
a crucial role in both the rate of interaction and the properties of the
observed photon. However, with a predicted frequency in the radio band (200MHz
- 200GHz) and a distinguishable spectral profile, next generation radio
telescopes may offer new opportunities for detection. The SKA-mid telescope has
a planned frequency range of 0.4 - 13.8GHz with optimal sensitivity in the
range $\sim$ 2 - 7 GHz. Considering observations at $\sim 500$MHz, the limiting
sensitivity is expected to be $\sim 0.04$mK based on a 24 hour integration
time. This compares with a predicted CDM axion all-sky signal temperature of
$\sim 0.04$mK using SKA Phase 1 telescopes and up to $\sim 1.17$mK using a
collecting area of (1km)$^2$ as planned for Phase 2.
