cosmology

The collapse of large-amplitude primordial curvature perturbations into planetary-mass primordial black holes generates a scalar-induced gravitational-wave background in the microhertz range that may be detectable by future Lunar Laser Ranging and Satellite Laser Ranging data. We derive projected constraints on the primordial black hole population from a null detection of such a background, including the impact of the electroweak phase transition, and discuss the connection to recent microlensing observations of the Andromeda Galaxy.

We study the cosmology of axions in the post-inflationary scenario, where random initial conditions and the ensuing string-domain-wall network generate an isocurvature power spectrum. For subdominant axion fractions, the resulting white-noise fluctuations enhance the growth of structure in the dominant component. Combining ultraviolet luminosity functions of galaxies with Lyman-$\alpha$ and CMB data yields leading cosmological limits on post-inflationary axion dark matter, linking early-universe field dynamics to high-redshift structure formation.

The detection of compact binary mergers with sub-solar masses at gravitational-wave observatories could mark the groundbreaking discovery of primordial black holes. Concurrently, evidence for a nHz stochastic gravitational wave background observed by pulsar timing arrays could suggest a non-astrophysical origin, potentially arising from scalar-induced gravitational waves. In this work, we analyze the connection between the two phenomena in the case where they share a common origin: the collapse of large primordial curvature perturbations in the early universe.

We present updated constraints on the abundance of primordial black holes (PBHs) dark matter from the high-redshift Lyman-$\alpha$ forest data from MIKE/HIRES experiments. Our analysis leverages an effective field theory (EFT) description of the 1D flux power spectrum, allowing us to analytically predict the Lyman-&alpha fluctuations on quasi-linear scales from first principles.

Recent observations have granted to us two unique insights into the early Universe: the presence of a low-frequency stochastic gravitational wave background detected by the NANOGrav and Pulsar Timing Array experiments and the emergence of unusually massive galaxy candidates at high redshifts reported by the James Webb Space Telescope. We consider the possibility that both observations have a common origin, namely supermassive primordial black holes.