The detection of gravitational-wave events revealed that there are numerous populations of black hole (BH) binaries that can merge within the age of the Universe. Although several formation channels of such binaries are known, considerable theoretical uncertainties associated with each channel defeat the robust prediction of how much each channel contributes to the total merger rate density. Given that the time evolution of the merger rate density in some channels is (exactly or nearly) independent of BH masses, clarifying this feature from observational data will shed some light on the nature of BH binaries. On the basis of this motivation, we formulate a methodology to perform a statistical test of whether the mass distribution of BH mergers evolves over time by hypothesis testing. Our statistical test requires neither a priori specification of the mass distribution, which is largely uncertain, nor that of the time dependence of merger rate. We then apply it to mock data for some concrete shapes of the merger rate density and show that the proposed method rejects/(does not reject) the null hypothesis correctly for a large sample size. After this verification, the method is applied to a catalog of the gravitational-wave events obtained during the LIGO-Virgo's third observing run. We find that the selection bias degrades the effectiveness of our method for the O3 catalog owing to the reduction in the number of and the maximum redshifts of the merger events that we can explore. Within the range where the method can be applied, there is no indication of the time evolution of the mass distribution of merger rate density. This limitation will be eased in future observations containing more events, and our hypothesis testing will help determine whether the merger rate density evolves over time independently of BH masses.
The merger history of primordial-black-hole binaries
作为暗物质的候选者，原初黑洞（PBH）由于可能是LIGO/Virgo观测到的重双星黑洞（BBH）的祖先而受到越来越多的关注。准确估计PBH双星的合并速率对于重建PBH双星的质量分布至关重要。指出了多核聚变堆的合并历史可能会改变多核聚变堆的合并率分布，这取决于多核聚变堆的质量函数。本文利用LIGO/Virgo O 1和O2观测运行中的10个BBH事件，通过考虑合并历史的影响来约束PBH的合并率分布。研究发现，第二次兼并对总兼并率的贡献是次显性的，因此兼并历史效应可以忽略不计。
Merger rate of initially clustered primordial black holes for the two-body channel
Theory Center, Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK)（高能加速器研究机构粒子与核研究研究所理论中心）；ICRR, University of Tokyo（东京大学宇宙射线研究所）；Kavli IPMU (WPI), UTIAS, University of Tokyo（东京大学 Kavli 宇宙起源与物质研究所（世界顶尖学术研究中心）、宇宙前沿机构）；RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), RIKEN（理化学研究所交叉理论与数学科学中心）；Department of Physics, Tohoku University（东北大学物理学系）
Black Hole Mergers as the Fastest Photon Ring Scramblers
National Sun Yat-Sen University（国立中山大学）；National Center for Theoretical Sciences（国家理论科学中心）；New York University, Abu Dhabi（纽约大学阿布扎比分校）；CERN（欧洲核子研究组织）；National Technical University of Athens（雅典国立技术大学）；University of Cambridge（剑桥大学）；INFN, Sezione di Roma（意大利国家核物理研究所罗马分部）
GW231123: Likely a product of successive mergers from $\sim 10 $ stellar-mass black holes
Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences（暗物质和空间天文重点实验室，中国科学院紫金山天文台）；Department of Physics, University of Florida（佛罗里达大学物理系）；School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）
Merger rates in primordial black hole clusters without initial binaries
原始的黑洞通过宇宙密度波动的崩溃而形成，被假设为宇宙中暗物质含量的贡献者。与此同时，它们的合并可能有助于最近观察到的引力波源的数量。我们调查的情况下，原始黑洞形成双星在宇宙的后期。具体来说，我们重新审视合并的原始黑洞在小集群的~30个对象的初始双星的情况下。双星通过牛顿引力相互作用动态地形成。这些双星作为星系团的热源，增加了星系团的速度色散，这抑制了通过引力波两体捕获的直接合并。与此同时，紧密双星的三体相遇太罕见了，以至于无法使双星足够紧密，从而使它们通过引力波辐射合并。我们的结论是，在没有初始双星的情况下，Bird et al.（2016）初始星团配置中的原始黑洞的合并率至少比以前提出的低一个数量级，这使得引力波检测到这样的源是不可能的。
