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Abstract
We consider QCD axion models where the Peccei-Quinn symmetry is badly broken by a larger amount in the past than in the present, in order to avoid the axion isocurvature problem. Specifically we study supersymmetric axion models where the Peccei-Quinn symmetry is dynamically broken by either hidden gauge interactions or the SU(3)c strong interactions whose dynamical scales are temporarily enhanced by the dynamics of flat directions. The former scenario predicts a large amount of self-interacting dark radiation as the hidden gauge symmetry is weakly coupled in the present Universe. We also show that the observed amount of baryon asymmetry can be generated by the QCD axion dynamics via spontaneous baryogenesis. We briefly comment on the case in which the PQ symmetry is broken by a non-minimal coupling to gravity.
Highlights
The strong CP phase is constrained to be less than 10−10 by the neutron EDM experiments [1], and the problem of why it is so small is known as the strong CP problem
In this paper we have proposed an extension of the QCD axion model to avoid the isocurvature constraint by suppressing quantum fluctuations of the axion
The dynamical scale can be temporarily enhanced during inflation, if the renormalization group flow of the gauge coupling is significantly modified by a flat direction with a large vacuum expectation value (VEV)
Summary
The strong CP phase is constrained to be less than 10−10 by the neutron EDM experiments [1], and the problem of why it is so small is known as the strong CP problem. In this paper we study a possibility that the PQ symmetry is largely broken temporarily in the early Universe, and discuss their cosmological implications based on a couple of models. We first discuss supersymmetric axion models in which the PQ symmetry is largely broken by non-Abelian hidden gauge interactions which are strongly coupled during inflation. The QCD scale can be enhanced if the HuHd flat direction acquires a large VEV in the early Universe [29, 25]. In Appendix we briefly discuss the case in which the PQ symmetry is broken by an interaction between the axion and the Ricci scalar
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