PhD Defense Public Talk
Aug
3
2026
Aug
3
2026
Description
Imprint of the Primordial Black Holes over Cosmic History
Primordial black holes (PBHs), formed from the gravitational collapse of large density perturbations in the early Universe, remain a viable dark matter candidate across several allowed mass windows and a possible origin of the supermassive black holes (SMBHs) recently inferred from recent JWST observations. While renewed interest has been driven by discoveries from JWST and gravitational-wave observatories, a unified framework connecting PBH physics to observable signatures across cosmic history has been lacking.
In this dissertation, I combine analytical modeling with cosmological hydrodynamic simulations to investigate the role of PBHs over a broad range of masses, from stellar-mass objects to massive (～10^{6-7} M_sun) seeds. I show that even a small abundance of massive PBHs can significantly reshape early structure formation. Their Poisson fluctuations generate an isocurvature contribution to the small-scale matter power spectrum, modifying the high-redshift halo mass function and accelerating the assembly of the first minihalos. These changes propagate to earlier star formation and alter the thermal and chemical evolution of the first galaxies. Accreting stellar-mass PBHs produce distinctive signatures in the high-redshift X-ray background and 21 cm signal, while massive PBHs provide a natural pathway for the formation of SMBHs before the assembly of their host galaxies, with implications for the low-frequency gravitational-wave background. Bringing this framework into direct comparison with observations, I demonstrate that PBH seeding reproduces the observed black hole--to--stellar mass ratios and redshift evolution of the overmassive AGN population discovered by JWST, including individual systems such as Abell~2744--QSO1 and the He~II emitter Hebe.
These results establish PBHs as a quantitatively testable framework for understanding the first stars, galaxies, and SMBHs, and provide a theoretical foundation for future tests with the Roman Space Telescope, SKA, Einstein Telescope, and LISA.
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