The absence of strong CP violation is among the most puzzling open questions of particle physics.
Within the Standard Model, the current experimental bound on the neutron EDM requires an extremely delicate cancellation of two seemingly unrelated physical quantities: the phase induced by the non-trivial topology of the QCD vacuum, and a combination of the complex phases present in the Higgs couplings to quarks. These two quantities must be opposite, to within one part in 10^10, which craves a new-physics explanation.
The most well-studied approach relies on introducing a new spontaneously broken symmetry, whose Goldstone boson, the axion, is able to dynamically enforce the absence of strong CP violation.
Motivated by recent renewed interests on both the theoretical and experimental sides, with novel axion models coming out and dedicated light scalar boson searches being planned, it is timely to discuss the current status of the strong CP puzzle and of its axionic solutions.
The workshop proper will be held on Tue 15 and Wed 16, and will be preceded by a one-day minischool on Mon 14, with basic lectures on symmetries and anomalies (F. Delduc, ENS Lyon), strong CP puzzle (M. Goodsell, LPTHE), EDM searches (Chen-Yu Liu, Indiana), and axion physics from low-energy (G. Villadoro, ICTP) to cosmology (A. Ringwald, DESY).