Axions are hypothetical particles that appear in well-motivated extensions of the Standard Model and are very attractive for being able to explain some of the open questions in particle physics, such as the strong CP-problem or the origin of dark matter in the universe. We will perform a thorough theoretical investigation of the phenomenological impact of axion interactions with SM particles, with special emphasis on hadronic particles at low energies. Although hadronically-coupled axions is an extensively studied model, its interactions at low energies are still not fully understood due to the interplay with non-perturbative QCD dynamics. As a result, many existing calculations of axion reaction rates have completely ignored any effects beyond naïve leading order in Chiral Perturbation Theory that are required for theoretical consistency. For some processes, this could lead to rate changes of orders of magnitude. Using the language of Effective Field Theories and dispersion relations we will build analysis frameworks that impose upon the hadronic amplitudes the most important constraints of scattering theory, such unitarity and analyticity together with QCD-specific constraints, and from these search for signals of undiscovered fundamental BSM particles at the hadronic scale, i.e. in the MeV-GeV mass range, with minimal model dependency.
The work will require state-of-the-art reading, as well as analytical and computational skills. It will be developed at the University of Barcelona, but remote supervision is possible.