The Phenomenological Landscape of Leptophilic ALPs

In this thesis, we consider model-building and phenomenology related to the simultaneous presence, alongside the Standard Model, of an Axion-Like Particle (ALP) and Heavy Neutral Leptons (HNLs). The former is naturally produced when global symmetries are spontaneously broken; the latter constitutes some of the most appealing candidates to “naturally” explain the smallness of neutrino masses. Altogether, this combination of particles naturally arises in Majoron models. We consider various UV models that could produce such a particle and possible mechanisms that could generate its mass radiatively. Bounds from flavour-, collider- and astro-searches are investigated.

Supervisor: Luca Merlo