Betelgeuse constraints on coupling between axionlike particles and electrons
Mengjiao Xiao, Pierluca Carenza, Maurizio Giannotti, Alessandro Mirizzi, K. Perez, O. Straniero, Brian W. Grefenstette
Abstract
Axionlike particles (ALPs) can be produced by thermal processes in a stellar interior, escape from the star and, if sufficiently light, be converted into photons in the external Galactic magnetic field. Such a process could produce a detectable hard x-ray excess in the direction of the star. In this scenario, a promising class of targets is the red supergiants, massive stars which are experiencing the late part of their evolution. We report on a search for ALP-induced x-ray emission from Betelgeuse, produced via the combined processes of bremsstrahlung, Compton and Primakoff. Using a 50 ks observation of Betelgeuse by the NuSTAR satellite telescope, we set 95% C.L. upper limits on the ALP-electron (${g}_{ae}$) and ALP-photon (${g}_{a\ensuremath{\gamma}}$) couplings. For masses ${m}_{a}\ensuremath{\le}(3.5--5.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$, we find ${g}_{a\ensuremath{\gamma}}\ifmmode\times\else\texttimes\fi{}{g}_{ae}<(0.4--2.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$ (depending on the stellar model and assuming a value of the regular Galactic magnetic field in the direction transverse to Betelgeuse of ${B}_{T}=1.4\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{G}$). This corresponds to ${g}_{ae}<(0.4--2.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ for ${g}_{a\ensuremath{\gamma}}>1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$. This analysis supercedes by over an order of magnitude the limit on ${g}_{ae}\ifmmode\times\else\texttimes\fi{}{g}_{a\ensuremath{\gamma}}$ placed by the CAST solar axion experiment and is among the strongest constraints on these couplings.