arxiv.org/abs/2608.04801 Isochrone fitting of Galactic globular clusters - IX. Tip of the red-giant branch for 27 clusters and constraints on new particle physics
Using tip-of-the-red-giant-branch measurements for 27 globular clusters, with 24 in the main likelihood, researchers constrain the axion-electron coupling to g_ae below 6.4e-14 at 95% CL. The observed TRGB was fainter than standard cooling predicted, by about 0.078 mag.
— via arXiv — Astro-ph, G. A. Gontcharov, A. M. Kudashov, O. S. Ryutina, S. V. Troitsky
