Axion-like particle searches with MeerKAT and SKA

Abstract

In the past few years, the search for axion-like particles (ALPs) has grown significantly due to their potential to account for the total abundance of the cold dark matter (CDM) in the universe. The coupling between ALPs and photons allows the spontaneous decay of ALPs into pairs of photons. For ALPs condensed in CDM halos around galaxies, the stimulated decay of ALPs is also possible. In this work, we examine the detectability of the radio emissions produced from this process with forthcoming radio telescopes such as the Square Kilometer Array (SKA) and MeerKAT. Our results, using recent more realistic sensitivity estimates, show that previous non-observation upper-limits projected for the SKA were highly optimistic, with the limits from dwarf galaxy observations being weakened by an order of magnitude at least. Notably, our results also depend far more strongly on ALP mass than previously, due to the inclusion of frequency dependent degradation effects. We show that the strongest potential environment to probe ALPs is nearby radio galaxies (due to the strong photon enhancement factor). In addition, with the use of a visibility taper, ALPs in the mass range of 4.96 × 10-7 − 1.04 × 10-4 eV would have non-observation upper limits on the ALP-photon gaγ in the range of 1.83 × 10-12 − 7.69 × 10-10 GeV-1 with SKA. MeerKAT can only produce limits similar to the CAST experiment within 50 hours of observation. Finally, we demonstrate that magnetic conversion of CDM ALPs to photons, in galactic magnetic fields, is highly sub-dominant, even to spontaneous decay.

Searching for relativistic axions in the sky

“…The projected sensitivity obtained with just ∼100 hours of observation of local dSphs is typically already well above the reach of ADMX, HAYSTAC and DMRadio. Similar studies of SKA reach, but for axion cold dark matter with m a 10 −8 eV were performed in [38] using the Galactic center, in [39] using nebulae and other compact objects, in [40] using dSphs, in [41] using neutron star, the Galactic center and Galaxy cluster and in [42] using Globular cluster respectively as sources of radio signals as well as in [43] where multiple different sources were used. In contrast, the relativistic axions probed by SKA are much lighter, m a 10 −12 eV, when constraints on axion-photon couplings [44][45][46] are taken into account.…”

“…is the Bose enhanced effective χ → aa decay rate, while Γ χ is the perturbative decay rate (for a related discussion of stimulated a → γγ decays see [43,54,55]). Axion density at a radial distance r from the center of dSph is given by,…”

Feebly-interacting particles: FIPs 2020 workshop report

“…In [599] it is pointed out for the first time that the echo signal relies on the historical luminosity of the photon source, unlike that the forward-going signals studied in Ref. [641,642,643] require the brightest radio sources today. This opens up the possibility to probe axion DM with time-varying radio sources that may be dim today but were once very bright, such as supernova remnants (SNRs).…”