We demonstrate that next-generation cosmic microwave background spectral distortion and pulsar timing array experiments can either detect signatures of primordial black holes in the mass range $\mathcal{O}(0.1–{10}^{12})M_{\odot }$, which are sourced from primordial overdensities within the standard thermal history of the universe, or constrain their existence to a negligible abundance, ruling them out as super-massive black hole seeds. Our conclusions are robust to changes in (i) the statistical properties of primordial density fluctuations, (ii) primordial black hole merger and accretion history and (iii) clustering statistics.

• Received 15 September 2020
• Accepted 1 March 2021

DOI:https://doi.org/10.1103/PhysRevD.103.063519