An even lighter QCD axion

  title={An even lighter QCD axion},
  author={Luca Di Luzio and Belen Gavela and Pablo Quilez and Andreas Ringwald},
  journal={Journal of High Energy Physics},
We explore whether the axion which solves the strong CP problem can naturally be much lighter than the canonical QCD axion. The $Z_\mathcal{N}$ symmetry proposed by Hook, with $\mathcal{N}$ mirror and degenerate worlds coexisting in Nature and linked by the axion field, is considered in terms of generic effective axion couplings. We show that the total potential is safely approximated by a single cosine in the large $\mathcal{N}$ limit, and we determine the analytical formula for the… 
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