Speaker
Description
Primordial black holes (PBHs) formed in the early Universe are a well-motivated dark matter candidate and a potential source of gravitational waves (GWs). In this work, we investigate the GW signals originating from early-formed PBH binaries, with a particular focus on the impact of primordial clustering induced by non-Gaussianity in the curvature perturbations. We model the spatial distribution of PBHs using higher-order correlation functions, incorporating the effects of local-type non-Gaussianity on both the two-point and three-point correlation functions.
We show that clustering significantly modifies the initial conditions of PBH binaries, including their typical separations and angular momentum, thereby affecting their merger timescales and survival probability against early disruption. While previous studies have primarily focused on the role of the two-point correlation function, we explicitly compute the PBH three-point correlation function and consistently include its contribution. We find that three-body correlations play a non-negligible role: they can enhance the probability of close encounters, while simultaneously increasing the rate of binary disruption through early three-body interactions. As a result, the present-day merger rate exhibits a non-trivial dependence on the level of primordial non-Gaussianity, including a critical threshold beyond which the merger rate is significantly suppressed.
We further compute the stochastic gravitational-wave background generated by the cosmic population of PBH mergers, incorporating the modified merger history due to clustering. Our results show that primordial clustering can substantially alter both the amplitude and spectral shape of the GW background, potentially bringing predictions into agreement with current observational bounds or within the reach of future GW experiments. This work highlights the crucial role of primordial non-Gaussianity and higher-order clustering in connecting PBH formation scenarios with gravitational-wave observations.