The QCD axion and axion-like particles, as leading dark matter candidates, can also have interesting implications for dark matter substructures if the Peccei-Quinn symmetry is broken after inflation. In such a scenario, axion perturbations on small scales will lead to the formation of axion miniclusters at matter-radiation equality, and subsequently the formation of axion stars. Such compact objects open new windows for indirect searches for axions. We compute the axion star mass function based on recent axion minicluster studies and Bose star simulations. Applying this mass function, we find post-inflation axion-like particles with masses 1.8 × 10^-21 eV <m _a < 3.3 × 10^-17 eV are constrained by the lack of dynamical heating of stars in ultrafaint dwarfs. We also find that current microlensing surveys are insensitive to QCD axion stars. While we focus on the gravitational detectability of axion stars, our result can be directly applied to other interesting signatures of axion stars, e.g. their decay to photons, that require as input the abundance, mass, and density distribution of axion stars.

中文翻译：

---

轴子星：质量函数和约束


QCD 轴子和类轴子粒子作为暗物质的主要候选者，如果佩切-奎因对称性在膨胀后被打破，也可能对暗物质子结构产生有趣的影响。在这种情况下，小尺度的轴子扰动将导致物质辐射相等的轴子小团簇的形成，并随后形成轴子星。这种紧凑的物体为间接搜索轴子打开了新的窗口。我们根据最近的轴子小星团研究和玻色星模拟计算了轴子星质量函数。应用这个质量函数，我们发现膨胀后轴子状粒子的质量为 1.8 × 10 ^-21 eV <米_a < 3.3 × 10 ^-17 eV 受到超微弱矮星中恒星缺乏动态加热的限制。我们还发现当前的微透镜巡天对 QCD 轴子星不敏感。虽然我们专注于轴子星的引力可探测性，但我们的结果可以直接应用于轴子星的其他有趣特征，例如它们衰变为光子，这需要轴子星的丰度、质量和密度分布作为输入。