| Name: Saurabh Kumar |
| Affiliation: Chennai Mathematical Institute |
| Conference ID: ASI2026_641 |
| Title: Properties of the merger sites of dynamically formed LIGO-Virgo-KAGRA binary black holes |
| Abstract Type: Poster |
| Abstract Category: High Energy Phenomena, Fundamental Physics and Astronomy |
| Author(s) and Co-Author(s) with Affiliation: Saurabh Kumar(Chennai Mathematical Institute, Siruseri, 603103, India), Parthapratim Mahapatra(Cardiff University, Cardiff, CF24 3AA, United Kingdom), K G Arun(Chennai Mathematical Institute, Siruseri, 603103, India) |
| Abstract: We apply a parametric model of forward evolution for black hole populations in dense, cluster-like environments to interpret the properties of the observed LIGO-Virgo-KAGRA (LVK) binary black hole (BBH) population. The detection of BBH mergers with component masses within the pulsational pair-instability supernova gap ($\sim 50\,M_\odot$–$130\,M_\odot$) significantly challenges standard stellar evolution models, while hierarchical mergers in dense stellar systems provide a natural route to populate this regime. We present a hierarchical Bayesian inference analysis of the Gravitational-Wave Transient Catalog 3 (GWTC-3) using our Simple Parametric model for Hierarchical Mergers (SPHM). The SPHM framework evolves BBH populations within gravitationally bound systems by employing numerical relativity fitting formulas for merger remnant masses, spins, and kicks, while accounting for pairing probabilities dependent on both total mass and mass ratio. We perform an end-to-end inference of global population hyperparameters, including the black hole initial mass function, pairing probability exponents, and the redshift-dependent merger rate density, and discuss what these imply for the properties of clusters where they are formed. Unlike previous studies, our analysis extends to $3\mathrm{G}$+$3\mathrm{G}$ generations, enabling a comprehensive reconstruction of the tails in the mass and spin distributions. We find that the multi-modal features and localized overdensities in the GWTC-3 primary mass spectrum—specifically the peaks observed at $m_1 \simeq 10\,M_\odot$, $17\,M_\odot$, and $35\,M_\odot$—can be self-consistently interpreted as contributions from higher merger generations in dense environments. Our results indicate that the observed absence of a sharp cutoff at $60\,M_\odot$ is consistent with a non-negligible retention fraction of merger remnants. Furthermore, we include branching ratios for various $N\mathrm{g}$–$M\mathrm{g}$ channels within our Bayesian inference, facilitating a direct interpretation of how specific hierarchical sequences contribute to the black hole mass spectrum. Our analysis demonstrates the effectiveness of semi-analytical models constructed from first principles in interpreting the population properties of compact binaries using gravitational wave observations. |
