Looking for axions in exotic, highly magnetised White Dwarf stars

The Peccei-Quinn (PQ) symmetry is a potential extension of the Standard Model that offers a compelling solution to the strong CP problem. This symmetry predicts the existence of a new pseudoscalar particle, the QCD axion, which, along with more general axion-like particles (ALPs), is also a viable dark matter candidate. This thesis focuses on the production of axions in highly magnetized white dwarfs (MWDs) through axion bremsstrahlung and their subsequent conversion into X-ray photons in the star’s strong magnetic field. Since astrophysical processes are generally not expected to produce a similar signature, the observation of such a signal could provide strong evidence for the existence of axions. This thesis systematically outlines the procedure for constructing a template for the axion-induced X-ray signal expected from isolated MWDs and shows how this prediction can be used to conduct a statistical analysis of observational data to set constraints on axion interaction strengths. Numerical techniques are then employed to apply this analysis to data from MWD RE J0317-853 observed by the Chandra telescope, yielding axion bounds consistent with recent work by Dessert et al. (2019, '22). Finally, this thesis critically examines the currently used methodology and suggests possible extensions and improvements to obtain more accurate statistical inference on axion models with future data.