Seminar by Antonio Herrero: “Non-anomalous axions: lessons from the Majoron”

Title: Non-anomalous axions: lessons from the Majoron

Speaker: Antonio Herrero

Venue & Time: Red Room / 15:00

Abstract: Axion-like particles are among the best-motivated candidates for physics beyond the Standard Model. They often arise as pseudo-Goldstone bosons of anomalous $U(1)$ symmetries. In such scenarios, non-perturbative effects associated with the anomaly give them a mass and can lead to domain wall formation, while the anomaly itself induces $a F \tilde{F}$ couplings. In this seminar we will revisit this picture in the case where anomalous and non-anomalous global symmetries are spontaneously broken at the same time. We will show that the Goldstone boson is then associated with the non-anomalous combination, and focus on two main consequences. First, for the Majoron, this result implies that its underlying symmetry is $B-L$ rather than $L$, which resolves the apparent domain wall problem. Second, $a F \tilde{F}$ couplings do not uniquely signal an anomalous origin, so non-anomalous Goldstone bosons could be probed in axion-like searches.