Ultra-light primordial black holes (PBHs) with masses MPBH < 5 × 108g can dominate transiently the energy budget of the Universe and reheat the Universe through their evaporation taking place before Big Bang Nucleosynthesis. The isocurvature energy density fluctuations associated to the inhomogeneous distribution of a population of such PBHs can induce an abundant production of GWs due to second-order gravitational effects. In this work, we discuss the effect of primordial non-Gaussianity on the clustering properties of PBHs and study the effect of a clustered PBH population on the spectral shape of the aforementioned induced GW signal. In particular, focusing on local-type non-Gaussianity we find a double-peaked GW signal with the amplitude of the low-frequency peak being proportional to the square of the non-Gaussian parameterτNL. Remarkably, depending on the PBH mass MPBH and the initial abundance of PBHs at formation time, i.e. ΩPNH,f, this double-peaked GW signal can lie well within the frequency bands of forthcoming GW detectors, namely LISA, ET, SKA and BBO, hence rendering this signal falsifiable by GW experiments and promoting it as a novel portal probing the primordial non-Gaussianity.

中文翻译：

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来自原始黑洞等曲率的引力波：非高斯性的影响


质量为 MPBH < 5 × 108g 的超轻原始黑洞 （PBH） 可以瞬时主导宇宙的能量预算，并通过它们在大爆炸核合成之前发生的蒸发来重新加热宇宙。由于二阶引力效应，与此类 PBH 种群的不均匀分布相关的等曲率能量密度波动可以诱导 GW 的大量产生。在这项工作中，我们讨论了原始非高斯性对 PBHs 聚类特性的影响，并研究了聚类 PBH 群体对上述诱导的 GW 信号的光谱形状的影响。特别是，专注于局部类型的非高斯分布，我们发现了一个双峰值 GW 信号，其低频峰值的幅度与非高斯参数 τNL 的平方成正比。值得注意的是，根据 PBH 质量 MPBH 和形成时 PBH 的初始丰度，即 ΩPNH，f，这个双峰 GW 信号可以很好地位于即将推出的 GW 探测器（即 LISA、ET、SKA 和 BBO）的频带内，因此使该信号可被 GW 实验证伪，并将其推广为探测原始非高斯性的新门户。