Davide Racco: "Revisiting Isocurvature Bounds on the Minimal QCD Axion"

Thursday 26 Feb 2026, 13:30 → 15:30 Europe/Rome

Sala Direzione INFN

The QCD axion is a well-motivated candidate for dark matter. For one of the two cosmological histories for this candidate, the pre-inflationary scenario, the PQ symmetry is not restored after inflation. Depending on the inflationary Hubble rate, this scenario can be constrained by the strong limits on its isocurvature perturbations on large scales.
We discuss how this constraint is naturally evaded when the quartic coupling of the complex U(1)_PQ field is small and its vev is enhanced during inflation, and how this solution is not jeopardised by parametric resonance over a significant portion of parameter space. The common lore, that isocurvature is a potential downside of the pre-inflationary axion, might be less stringent than what is commonly thought.