Experimental Limits on Planetary Mass Primordial Black Hole Mergers

Abstract

The multi-mode acoustic gravitational wave experiment (MAGE) is a high-frequency gravitational wave detection experiment featuring cryogenic quartz bulk acoustic wave resonators operating as sensitive strain antennas in the MHz regime. After 61 days of non-continuous data collection, we present bounds on the observable merger rate density of primordial black hole binary systems of chirp mass $1.2\times10^{-4}M_\odot<\mathcal{M}<1.7\times10^{-9}M_\odot$. The maximum achieved limit on the merger rate density is $\mathcal{R}>1.3\times10^{18}~\mathrm{kpc}^{-3}\mathrm{yr}^{-1}$ which corresponds to constraining yearly mergers to a distance of reach on the order of the solar system, or $1.0\times10^{-6}$ kpc during the observational period. In addition, we exclude significantly rare and strong events similar to those observed in previous predecessor experiments as non-gravitational background signals, utilising coincident analysis between multiple detectors.

Figures (4)

• Figure 1: a) Schematic of experimental setup for MAGE featuring the cryogenic system and data acquisition chain. b) Experimental strain sensitivity of each resonant mode used in this work.
• Figure 2: Instantaneous vibrational energy of a single mode is plotted as a histogram for a 23 minute segment of data. The blue (orange) histogram represents the energy distribution before (after) optimal filtering. Both histograms clearly follow an expected $\chi^2$ distribution, however the effect of optimal filtering greatly reduces the effective temperature at which events can be identified with SNR = 1.
• Figure 3: Integral histogram of triggers that passed the selection criteria $\mathcal{R}_{N >\rho^2}$ are shown as a function of energy SNR $\rho^2$. Dashed lines indicate the triggers that remain after the data set is refined by coincident counts. A $\chi^2$ model fit to the distributions of detector one is shown by the black lines. Clear separation between two distributions can be seen be defined by the shaded region under the $\chi^2$ fit.
• Figure 4: The excluded merger rate density of PBH binary systems determined in this work is plotted as the green shaded region. Also shaded are areas that have been excluded by previous experiments Chou2017Miller2024Miller2022, although it must be noted that the LIGO exclusions rely on certain cosmological assumptions that are not made in this work Miller2024. Dashed lines give the density that excludes one event per year at a distance corresponding to various astrophysical objects for reference. The solid black line is the best case possible merger rate density of PBH binaries if they constituted 100% of local dark matter Muia2022. The red line represents an idealistic estimate for a future version of MAGE operating at a reduced temperature of 10 mK.