PBH & ABH merger rate discrimination (arXiv:2105.11139)

 

arXiv:2105.11139  [pdf, other] 

 

gr-qc astro-ph.CO astro-ph.HE

Can we distinguish astrophysical from primordial black holes via the stochastic gravitational wave background?

Authors: Suvodip Mukherjee, Joseph Silk

Abstract: One of the crucial windows for distinguishing astrophysical black holes from primordial black holes is through the redshift evolution of their respective merger rates. The low redshift population of black holes of astrophysical origin is expected to follow the star formation rate. The corresponding peak in their merger rate is going to peak at a redshift smaller than that of the star formation rate peak (zp≈2), depending on the time delay between the formation and mergers of black holes. Black holes of primordial origin are going to be present before the formation of the stars, and the merger rate of these sources at high redshift is going to be large. We propose joint estimation of a hybrid merger rate from the stochastic gravitational wave background, which can use the cosmic history of merger rates to distinguish between the two populations of black holes. Using the latest bounds on the amplitude of the stochastic gravitational wave background amplitude from the third observation run of LIGO/Virgo, we obtain weak constraints at 68% C.L. on the primordial black hole merger rate index 2.56+1.64−1.76 and astrophysical black hole time delay 6.7+4.22−4.74 Gyr. We should be able to distinguish between the different populations of black holes with the forthcoming O5 and A+ detector sensitivities. 

This looks like clean job, but My doubt: Can we consider a case where PBH merges with ABH ?

cnclsn:

We construct a hybrid model of the GW merger rates and source populations that is characterized by four parameters, namely the local merger rate of GW sources R GW 0 , the astrophysical time delay between formation and merger for ABHs t eff d , the power-law index of the merger rate for PBHs α, and the characteristic mass scale Mc of PBHs. We obtain constraints on R GW 0 , α, teff d from the stochastic GW background data of third observing run of the LIGO/Virgo collaboration O3 (Abbott et al. 2021) and the bounds on the local merger rate from individual events of the O3a (Abbott et al. 2020a,b) for three different mass choices (see Fig. 3). Current data can only rule out very large values of the parameter α and cannot constrain the time-delay parameter. However, in the near future from O5 and A+ sensitivities, the stochastic GW background should be a powerful probe that is capable of distinguishing between different populations of the GW sources. We show a forecast in Fig. 4, which indicates that accurate measurement of the parameter α, and constraints on the time-delay parameter t eff d , characteristic mass scale of PBHs Mc, and the fraction of PBH/ABH fP BH/ABH should be feasible at O5 (Abbott et al. 2016a) and A+ (Abbott et al. 2018a; Barsotti et al. 2020) sensitivities. By using the posteriors on the PBH population parameters such as α, Mc and fP BH/ABH, one can explore different models of PBH formation scenarios and can constrain the parameter space of those models (Zel’dovich & Novikov 1967; Hawking 1971; Carr 1975; Khlopov & Polnarev 1980; Khlopov et al. 1985; Carr 2005; Clesse & Garc´ıa-Bellido 2017; Ali-Ha¨ımoud et al. 2017; Raidal et al. 2017, 2019; Sasaki et al. 2018; Jenkins & Sakellariadou 2020; Atal et al. 2020). In future work, we will explore the measurability of the stochastic GW signal from space-based GW detectors such as Laser Interferometer Space Antenna (LISA) (AmaroSeoane et al. 2017) and the next generation ground-based detectors such as the Einstein Telescope (Punturo et al. 2010), and the Cosmic Explorer (Reitze et al. 2019). For future GW detectors we will be able to identify individual sources up to high redshift (z ∼ 50) than the detector horizon of current generation network of detectors (z ∼ 1). As a result, sources which are present only at very high redshift (z & 50) will contribute to the stochastic GW background signal for the next generation GW detectors. We should be able to unveil the population of high redshift GW sources. it should also be possible to explore the time dependence of the stochastic GW background (Mukherjee & Silk 2019, 2020). This could provide an independent means of distinguishing between different kinds of sources contributing in the stochastic GW background.