What Will Be The Minimum Testable Value of Abundance of Primordial Black Holes by Future GW Experiments? (Cosmology)

Recent detection of gravitational waves (GWs) by Advanced LIGO/VIRGO from black holes mergers raise the possibility that primordial black holes (PBHs) may contain a significant amount of dark matter in the universe.

In particular, Gabriele and colleagues recently found evidence for primordial black holes in LIGO/VIRGO GW-data and suggested that, we can confirm the primordial nature of a subpopulation of binary black holes (BBHs) with the help of third-generation Gravitational wave (GW) detectors, such as the Einstein Telescope and Cosmic Explorer. But, whether or not these detectors can confirm this hypothesis in the future, even a smaller value of PBH abundance (fPBH) may still have an impact on the cosmological evolution as far as large scale structure is concerned. It is therefore timely and interesting to ask what is the minimum testable value of fPBH by future GW experiments and this question is now addressed by Gabriele Francolini and colleagues in their recent paper.

In order to find the minimum PBH abundance testable by future detectors, they considered the largest possible PBH merger rate coming from primordial binaries.

Their findings indicated that an abundance as small as 10¯10 can be probed, in different mass ranges, by both 3G detectors and LISA in the case in which PBHs are clustered. They obtained similar figures by restricting to sufficiently large redshifts, even though in a smaller PBH mass range.

Fig 1: Minimum PBH abundance required to have at least one event per year at the ET (green) and LISA (yellow) experiments, for both cases of Poisson distributed (solid) and strongly clustered (dashed) PBHs. Superimposed on these curves they showed the present observational constraints (gray) coming from microlensing searches by Subaru HSC, MACHO/EROS (E), Ogle (O) and Icarus (I), X-rays (Xr) and X-Ray binaries (XRayB), CMB anisotropies, Dwarf Galaxy heating (DGH), dynamical friction (DF), the neutron-to-proton ratio (n/p) and CMB µ-distortions © G. Francolini et al.
FIG. 2: Minimum abundance for PBH evidence © G. Francolini et al.

For more:

Valerio De Luca, Gabriele Franciolini, Paolo Pani, and Antonio Riotto, “The Minimum Testable Abundance of Primordial Black Holes at Future Gravitational-Wave Detectors”, pp. 1-11, Arxiv, 2021.

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