Ken Ng, MIT

"Search for ultralight bosons and primordial black holes with a population of binary black holes – the present and the future"

Abstract: The growing catalog of binary black holes (BBHs) allows for unprecedented studies in different fields of physics. In this talk, I will present how gravitational-wave (GW) measurements can be utilized to search for ultralight bosons and primordial black holes (PBHs), which are proposed to solve some of the questions about our Universe. In the first half, I will discuss the current constraints on excluding the mass of ultralight bosons, [1.3, 2.7] x 10^-13 eV, based on the mass-spin measurements of BBHs. These constraints are driven by the phenomenology called “superradiance”, which extracts the angular momentum of a rapidly spinning black hole to form a slowly spinning black hole-boson cloud system. In the second half, I will illustrate how the distance measurements of very high-redshift BBHs made by the next-generation GW detectors may provide cleaner hints or constraints for the existence of PBHs in the future. Considering a population of high-redshift BBHs, one may measure the relative fraction of PBH binaries to the BBHs originated from Population III stars at ~10% precision.