White dwarfs as a probe of light QCD axions

Reuven Balkin, Javi Serra, Konstantin Springmann, Stefan Stelzl, Andreas Weiler

Submitted on 4 November 2022


We study the effects of light QCD axions on the stellar configuration of white dwarfs. At finite baryon density, the non-derivative coupling of the axion to nucleons displaces the axion from its in-vacuum minimum which implies a reduction of the nucleon mass. This dramatically alters the composition of stellar remnants. In particular, the modifications of the mass-radius relationship of white dwarfs allow us to probe large regions of unexplored axion parameter space without requiring it to be a significant fraction of dark matter.


Comment: 6 pages, 3 figures

Subjects: High Energy Physics - Phenomenology; Astrophysics - High Energy Astrophysical Phenomena; Astrophysics - Solar and Stellar Astrophysics


Constraints and future projections on the axion parameter space. Exclusions from modifications of the white dwarf $M\,$-$\,R$ relation are shown in red. The observation of WDs close to the Chandrasekhar limit can further probe the parameter space until the orange dashed line. The solid black line shows the QCD axion with $m_{\phi}f=\mpi\fpi$. For reference, we plot $f = M_{\text{P}}$ in gray. Further bounds originate from the sourcing in the Sun \cite{Hook:2017psm} (blue), the supernova 1987A (green), and black hole superradiance \cite{Arvanitaki:2014wva} (yellow). Finally, we show which parameters lead to a new ground state accessible in neutron stars (dot-dashed purple); for more details see \cite{Balkin:2022}.