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arXiv · 2609.27159

Axions and the RR Lyrae Period-Luminosity Relation

Jeremy Sakstein·Djuna Croon
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Abstract

We investigate the impact of axions on the period-luminosity relation (PLR) of RR Lyrae stars. During the red giant branch phase, emission through the electron coupling cools the core, increasing its mass at ignition. The larger core produces more luminous horizontal-branch stars, systematically shifting the zero point of the RR Lyrae PLR toward brighter magnitudes. We model the RR Lyrae population of the globular cluster M3 using stellar evolution and pulsation calculations tailored to its age and composition, and compare the resulting synthetic $K_s$-band PLR with observations. For $α_{26}\equiv 10^{26}g_{ae}^2/4π=0.5$, the axion-induced shift in the predicted PLR is comparable to the current uncertainty in the absolute M3 zero-point calibration.

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Jeremy Sakstein, Djuna Croon. 2026-09-22. Axions and the RR Lyrae Period-Luminosity Relation. https://arxiv.org/abs/2609.27159

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