Astrophobic Axions

• Enrico Nardi

Reliable estimates of the allowed range for axion couplings to photons, nucleons and electrons are of major importance for determining the viable axion mass window as well as to focus experimental axion searches. We show that in a class of generalized DFSZ axion models with generation dependent Peccei-Quinn charges the axion couplings to nucleons and electrons can be simultaneously suppressed, thus relaxing the limits on the axion mass from the SN1987A burst duration and from white dwarf cooling.

Peccei-Quinn Symmetry as a Flavor Symmetry

• Fredrik Bjorkeroth (INFN-LNF)

There has been recent interest in possible connections between a Peccei-Quinn (PQ) symmetry and quark flavour structures. I describe how a generic generation-dependent U(1) symmetry acting on the quark Yukawa operators can reduce the number of free parameters in the quark sector. The maximal reduction compatible with CP violation yields nine real parameters and one phase, which matches the number of physical observables, implying that such models have no free parameters. This has several interesting consequences: (i) there are only two inequivalent textures, each one giving rise to six different models depending on quark flavour assignments, (ii) the U(1) symmetries that generate these textures all have a QCD anomaly, and hence are PQ symmetries, (iii) the resultant axion has flavour-violating couplings to quarks, which can be probed in meson decays, (iv) in some cases the contributions to the QCD anomaly of two generations cancels out, opening up the possibility that the axion coupling to nucleons is strongly suppressed.

Future challenges for Axion Physics

• Luca Visinelli

In this talk, I want to provide with some topics that I consider interesting to be explored in the near future. In particular, I will discuss a few ideas for small and big projects that could be developed in relation with axion physics, with a particular attention to the role of substructures.

Bounds and Hints on Axions from Stars

• Maurizio Giannotti

Stars are powerful laboratories to study light, weakly interactive particles. In particular, considerations about stars and stellar evolution have led to strong bounds on axion like particles (ALPs), hidden photons, anomalous electromagnetic properties of neutrinos, etc. More recently, observations of excessive stellar energy losses have led to the appealing idea that new-physics (most likely, ALPs) may be playing a role in stellar cooling. I will review the stellar bounds and hints on ALPs and discuss the current experimental potential to probe the hinted parameter space.