Production of thermal axions across the electroweak phase transition

• Published in: Journal of cosmology and astroparticle physics Vol. 2021; no. 3; p. 90
• Main Authors: Arias-Aragón, Fernando, D'Eramo, Francesco, Ferreira, Ricardo Z., Merlo, Luca, Notari, Alessio
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.03.2021
• Subjects: axions; cosmology of theories beyond the SM; Couplings; Flavor (particle physics); Hierarchies; Neutrinos; Particle decay; particle physics - cosmology connection; Phase transitions; Standard model (particle physics); Thermal baths
• ISSN: 1475-7516; 1475-7516
• DOI: 10.1088/1475-7516/2021/03/090

Abstract Light axions can potentially leave a cosmic background, just like neutrinos. We complete the study of thermal axion production across the electroweak scale by providing a smooth and continuous treatment through the two phases. Focusing on both flavor conserving and violating couplings to third generation quarks, we compute the amount of axions produced via scatterings and decays of thermal bath particles. We perform a model independent analysis in terms of axion effective couplings, and we also make predictions for specific microscopic QCD axion scenarios. This observable effect, parameterized as it is conventional by an effective number of additional neutrinos, is above the 1σ sensitivity of future CMB-S4 surveys. Moreover, if one assumes no large hierarchies among dimensionless axion couplings to standard model particles, future axion helioscopes will provide a complementary probe for the parameter region we study.