Cosmological aspects of the clockwork axion

• Published in: The journal of high energy physics 2018-07, Vol.2018 (7), p.1-29, Article 66
• Main Author: Long, Andrew J.
• Format: Article
• Language: English
• Subjects: Beyond Standard Model; Broken symmetry; Classical and Quantum Gravitation; Clockwork; Cosmology of Theories beyond the SM; Dark matter; Defects; Elementary Particles; High energy physics; Particle decay; Phase transitions; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Regular Article - Theoretical Physics; Relativity Theory; String Theory; Topological Strings; Universe
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP07(2018)066

A bstract The clockwork axion refers to a family of aligned multi-axion models that lead to an exponential hierarchy between the scale of Peccei-Quinn symmetry breaking and the scale of the axion decay constant. The clockworking can bring the Peccei-Quinn-scale particles to within reach of collider experiments. In this work we are interested in whether cosmological observations impose any new constraints on the clockwork axion. If the universe reheats above the scale of Peccei-Quinn breaking, then the ensuing cosmological phase transition produces a network of topological defects, which have a qualitatively different behavior from the string-wall network in the usual axion models. We estimate the relic abundances of axion dark matter and dark radiation that arise from the emission of axions by the defect network, and we infer a constraint on the scale of Peccei-Quinn breaking and the mass spectrum. We find that the defect contribution to the axion dark matter relic abundance is generally negligible. However, the defect production of relativistic axion dark radiation becomes significant if the scale of Peccei-Quinn symmetry breaking is larger than 100 TeV, and measurements of Δ N eff provide a new probe of this class of models.