Colloq Abstract - Quinn

July 12, 2019

11:00am Mountain

Peter Quinn (UWA)

A radio astronomy search for Cold Dark Matter axions

Abstract

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 ΩDM ∼ 0.26 in the standard ΛCDM model. Indeed, the value of ΩDM ∼ 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. Next generation telescopes such as the Square Kilometre Array (SKA) present an exciting opportunity for radio astronomy to contribute to the search for dark matter. We focus on the search for an axion, a particle predicted as a solution to the Strong CP Problem that could account for all of the dark matter density. Sikivie 1983 predicted the conversion of an axion in the presence of a magnetic field and there has been extensive research into the detectability of such a signal in the laboratory. We  focus on the static and inhomogeneous fields that pervade spiral galaxies and galaxy clusters and present a model of the spectral profile for a range of inter- and extra-Galactic observations. We find that the strength and scale of the astrophysical magnetic field is critical to the rate of non-resonant axion conversion, and the relative uncertainty of these characteristics in the astrophysical environment makes it challenging to conclude on the strength of an axion signature. Having assessed the opportunity for detection from the Milky Way, Andromeda, Coma cluster and Central Molecular Zone of the Milky Way, we find that each produces a unique spectral profile and that proximity to Earth appears to trump the larger volumes of distant objects. The Central Molecular Zone offers the best opportunity for detection from the sources considered, allowing axion couplings, gaγγ, of 2.1×10−12 −1.7×10−10GeV−1cε0 to be probed for axion masses 1.7−57μeVc−2 respectively. However, assumptions made about the strength and structure of the magnetic field are critical to this result and we examine these effects in detail.