Quantum Black Holes and the Primordial Universe

Abstract

Two central challenges of twenty-first century physics are to understand the quantum nature of regions of spacetime with strong curvature, such as black holes, and to uncover the composition and physical laws of the universe's dark sector, especially during the primordial era. This dissertation presents new theoretical results and experimental tools aimed at advancing our understanding of these fundamental problems. When quantum field theory is combined with classical black hole models, it predicts that black holes emit radiation and lose mass over time, potentially evaporating completely. However, there are unresolved questions about the origin of this radiation and its behavior near the event horizon. I present the most detailed numerical study to date of the quantum state near the horizon of a semi-classical Schwarzschild black hole, helping resolve conflicting ideas from previous research and offering new insights into the local temperature near the horizon. There are currently no observational data on evaporating black holes, or even any direct evidence that they evaporate at all. I explore the prospects of detecting warm, dark-sector relic particles emitted from evaporating primordial black holes through their impact on the large-scale structure of the universe. I show that these relics can be detected by current and future cosmological surveys and can be distinguished from thermally-produced relics. Additionally, I provide the strongest constraints on these relics to date, demonstrating that they can account for no more than about 2% of the dark matter across a broad region of their viable parameter space. Exploring the dark-sector of the universe and its primordial state requires reconstructing its early-time conditions from present-day observations. I present a novel method for reconstructing the initial matter density field from the late-time density field using convolutional neural networks. This method expands the range of high-fidelity reconstruction to much smaller scales than existing techniques, showing promise for exploring the properties of the primordial universe at smaller scales than ever before.