New scenario of QCD axion clump formation I: Linear analysis
  The QCD axion acquires the potential through the non-perturbative effect of
the QCD matters around the QCD phase transition. During this period, the direct
interaction between the axion and the QCD matters sets in. Focusing on the
impact of this direct interaction, we propose two scenarios where the
fluctuation of the axion can rapidly grow, potentially leading to the formation
of axion miniclusters even if the Peccei-Quinn (PQ) symmetry was already broken
during inflation. The first scenario assumes that the primordial curvature
perturbation at the horizon scale during the QCD epoch was significantly
enhanced and the second one assumes that the initial misalignment was tuned
around the hilltop of the potential.
