Speaker: Loris Del Grosso, Johns Hopkins University
Title:Â Primordial black holes, naturalness and other stories
Abstract: In the first part of the talk, I will review the generation of primordial black holes (PBHs) within the framework of single-field inflationary models and assess their compatibility with the cosmological history of the Universe. I will show that, depending on the masses of the formed PBHs, single-field inflation models require more than fine-tuning a potential to induce ultraslow roll; it necessitates a comprehensive understanding of the post-inflationary cosmological evolution. As an explicative example, I will introduce a new model, based on a double inflection point and consistent with cosmic microwave background observations, capable of generating subsolar PBHs, whose merger could be potentially detectable by the LVK experiment. In the second part, I will apply the criterion of finite naturalness to the limiting case of a generic heavy sector decoupled from the Standard Model. The sole and unavoidable exception to this decoupling arises from gravitational interactions. I will demonstrate that gravity can couple the Higgs to the heavy scale significantly earlier than the well-known three-loop top-quark-mediated diagrams discussed in previous literature. As an application, I will show that finite naturalness disfavors large-field inflationary models involving super-Planckian field excursions. In contrast, in the small-field regime, achieving successful inflation requires substantial fine-tuning of the initial conditions, in agreement with previous results. Recent data from the Atacama Cosmology Telescope further amplify the tension between naturalness and fine-tuning, challenging the theoretical robustness of single-field inflation as a compelling explanation for the origin of the universe. If time permits, I will conclude with a discussion of alternative cosmologies based on gauge theories with shadow charges, i.e. admissible states that violate Gauss’s law as a consequence of specific initial conditions.