Speaker
Fredrik Bjorkeroth
(INFN LNF)
Description
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.
