Elastic scattering of cosmological gravitational wave backgrounds: primordial black holes and stellar objects

Primordial black holes (PBHs) are plausible dark matter candidates that formed from the gravitational collapse of primordial density fluctuations. Current observational constraints allow asteroid -mass PBHs to account for all of the cosmological dark matter. We show that elastic scattering of a cosmological gravitational wave background, these black holes generate spectral distortions on the background of 0.3% for cosmologically relevant frequencies without considering coherent scattering and 5% when the coherent enhancement is included. Scattering from stellar objects induce much smaller distortions. Detectability of this signal depends on our ultimate understanding of the unperturbed background spectrum.