Observable dark radiation from a cosmologically safe QCD axion

Masahiro Kawasaki, Masaki Yamada, Tsutomu T. Yanagida

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)


We propose a QCD axion model that avoids the cosmological domain wall problem, introducing a global SU(3)f family symmetry in which we embed the unwanted Peccei-Quinn (PQ) discrete symmetry. The spontaneous breaking of SU(3)f and PQ symmetry predicts eight NG bosons as well as axion, all of which contribute to the energy density of the Universe as dark radiation. The deviation from the standard model prediction of dark radiation can be observed by future observations of cosmic microwave background fluctuations. Our model also predicts a sizable exotic kaon decay rate, which is marginally consistent with the present collider data and would be tested by future collider experiments.

Original languageEnglish
Article number125018
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Issue number12
Publication statusPublished - 2015 Jun 15


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