Title: QCD axion bubbles from the hidden SU(N) gauge symmetry breaking

Abstract: The QCD axion bubbles can be formed due to an extra Peccei-Quinn (PQ) symmetry breaking in the early Universe. In this paper, we investigate the QCD axion bubbles formation from the PQ symmetry broken by hidden $SU(N)_H$ gauge interactions after inflation, which leads to the multiple vacua. The axion acquires a light mass and then settles down into different vacua. The QCD axion bubbles are formed when the conventional QCD axion arises during the QCD phase transition. In our scenario, the QCD axions that start to oscillate at the large values $\sim2\pi/3$ can lead to the high density axion bubbles with $N=2$. The cosmological implications of the QCD axion bubbles are also discussed, such as the primordial black holes (PBHs) and the axion miniclusters. We find that the PBH mass is lager than $\sim\mathcal{O}(5\times10^5)M_\odot$ for the axion scale $f_a\sim\mathcal{O}(10^{16})\, \rm GeV$.