Axion spectra and the associated x-ray spectra of low-mass stars

Abstract

Axion particles are among the best candidates to explain dark matter and resolve the strong CP problem in the Standard Model. If such a particle exists, the core of stars will produce them in large amounts. For the first time, we predict the axion spectra and their associated luminosities for several low-mass stars – one and two solar masses stars in the main sequence and post-main sequence stages of evolution. Equally, we also compute the x-ray excess emission resulting from the conversion of axions back to photons in the presence of a strong magnetic field in the envelope of these stars. Hence, a given star will have a unique axion spectrum and La axion luminosity. And if such star has a strong magnetic field in its stellar envelope, it will also show a characteristic x-ray spectrum and Laγ x-ray luminosity. Such radiation will add up to the x-ray electromagnetic spectrum and LX luminosity of the star. The present study focuses on axion models with an axion-photon coupling constant, 5 10GeV, a value just below the most recent upper limit of 6.6 10GeV found by CAST and IAXO helioscopes. The range of axion parameters discussed here spans many axion models’ parameter space, including the DFSZ and KSVZ models. We found that axions with a mass in the range 10 to 10 eV and an axion-photon coupling constant of 5 10GeV produce an axion emission spectra with an averaged axion energy that varies from 1 to 5 KeV, and an La ranging from 10 to 7 10 L⊙. We also predict that Laγ varies from 5 10 to 10 L⊙ for stars with an averaged magnetic field of 3 10 G in their atmospheres. Most of these Laγ predictions are larger than the LX observed in some stars. Therefore, such preliminary results show the potential of the next generation of stellar x-ray missions to constrain several classes of axion models.