Thermal production of astrophobic axions

• Published in: The journal of high energy physics Vol. 2024; no. 9; pp. 136 - 52
• Main Authors: Badziak, Marcin, Harigaya, Keisuke, Łukawski, Michał, Ziegler, Robert
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 19.09.2024; Springer Nature B.V; SpringerOpen
• Subjects: Astronomical models; Axions and ALPs; Classical and Quantum Gravitation; Cosmic microwave background; Cosmology of Theories BSM; Couplings; Elementary Particles; Equilibrium; Hypothetical particles; Muons; Observatories; Physics; Physics and Astronomy; Quantum chromodynamics; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Regular Article - Theoretical Physics; Relativity Theory; Space telescopes; Standard model (particle physics); String Theory; Universe; Upper bounds; Cosmology of Theories BSM; Axions and ALPs
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP09(2024)136

A bstract Hot axions are produced in the early Universe via their interactions with Standard Model particles, contributing to dark radiation commonly parameterized as ∆ N eff . In standard QCD axion benchmark models, this contribution to ∆ N eff is negligible after taking into account astrophysical limits such as the SN1987A bound. We therefore compute the axion contribution to ∆ N eff in so-called astrophobic axion models characterized by strongly suppressed axion couplings to nucleons and electrons, in which astrophysical constraints are relaxed and ∆ N eff may be sizable. We also construct new astrophobic models in which axion couplings to photons and/or muons are suppressed as well, allowing for axion masses as large as few eV. Most astrophobic models are within the reach of CMB-S4, while some allow for ∆ N eff as large as the current upper bound from Planck and thus will be probed by the Simons Observatory. The majority of astrophobic axion models predicting large ∆ N eff is also within the reach of IAXO or even BabyIAXO.