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Pulsar Timing Array collaborations have recently announced the discovery of astochastic gravitational wave background (SGWB) at nanohertz frequencies. Weanalyze the GW signals from the domination of ultra-low mass primordial blackholes (PBHs) in the early universe and show that they can explain this recentdiscovery. This scenario requires a relatively broad peak in the power spectrumof scalar perturbations from inflation with a spectral index in a narrow rangeof $1.45$ to $1.6$. The resulting PBH population would have mass around$10^{8}$g, and the initial abundance $\beta_f$ lies between $10^{-10}$ and$10^{-9}$. We find that this explanation is preferred by the data over thegeneric model, assuming supermassive BHs as the source. These very light PBHswould decay before Big Bang Nucleosynthesis (BBN); however, upcomingthird-generation terrestrial laser interferometers would be able to test themodel by observing the GW spectrum produced during the formation of the PBHs.Also, the scalar power spectra associated with our scenario will be within thereach of PIXIE probing CMB spectral distortions.

Ultra-low mass PBHs in the early universe can explain the PTA signal