Gabriele Montefalcone Final Defense

Abstract: The universe carries within it the imprints of physical processes far beyond the reach of any terrestrial experiment. This dissertation develops theoretical predictions and observational tools to read these cosmic footprints, addressing open questions across three interconnected frontiers: the dynamics of inflation, the nature of dark matter, and the properties of cosmic neutrinos. Additional recent work probes the evidence for evolving dark energy in light of new observational claims.

As a representative example of this research program, this talk focuses on cosmic neutrinos and the cosmic microwave background. Despite interacting only very weakly with ordinary matter, the cosmic neutrino background influences the evolution of the early universe primarily through gravity, leaving a subtle but distinctive imprint on the CMB: a phase shift in the acoustic oscillations of the photon-baryon plasma prior to recombination. This signature can only be produced by free-streaming radiation under adiabatic initial conditions, making it a clean and robust probe of neutrino physics. I will present a framework to extract this effect directly from CMB observations and show that current data from Planck, ACT, and SPT detect it with high significance, consistent with the Standard Model prediction of three free-streaming neutrino species. I will then show how the same measurement can be used to test scenarios in which neutrinos interact more strongly than expected, delaying their decoupling from the primordial plasma. By directly mapping the observed phase shift onto the strength of these potential interactions, we place competitive constraints on new neutrino physics using a single, well-understood observable, without the need for dedicated model-dependent analyses.