5. Theoretical Physics (CSN4)

The dirty side of the axion

by Luca Di Luzio (GE)

Aula Direzione (LNF)

Aula Direzione


Via Enrico Fermi, 40 00044 Frascati (Roma)
Since the early 90’s it was understood that in order for the Peccei Quinn (PQ) mechanism to work the global U(1)_PQ had to be realized to an extremely high level of accuracy. In fact, even a tiny explicit breaking of the global PQ symmetry (e.g. via Planck-induced effective operators) would sizably contribute to the axion vacuum energy density and prevent the θ angle to relax to a value below the experimental upper bound |θ| < 10^-10. In this contribution, I will reproduce the standard argument and review possible mechanisms in order to protect the axion.