Constraining the Axion-Photon Coupling with Massive Stars

Understand

We point out that stars in the mass window ~ 8-12 Msun can serve as sensitive probes of the axion-photon interaction, g_{A\gamma\gamma}.

• Specifically, for these stars axion energy losses from the helium-burning core would shorten and eventually eliminate the blue loop phase of the evolution.
• This would contradict observational data, since the blue loops are required, e.g., to account for the existence of Cepheid stars.
• Using the MESA stellar evolution code, modified to include the extra cooling, we conservatively find g_{A\gamma\gamma} <~ 0.8 * 10^{-10} GeV^{-1}, which compares favorably with the existing bounds.