Speaker
Description
Axion-like particle (ALP) effective field theories (EFTs) provide a powerful, UV-agnostic framework for studying ALP phenomenology. Phenomenological analyses within this framework typically assume that the ALP mass lies well below the decay constant, i.e. $m_a << f_a$, following standard EFT intuition. In this poster, motivated by the analogous situation in chiral perturbation theory - where pseudo-Nambu-Goldstone pions can have masses comparable to the decay constant - we revisit the validity criterion of ALP EFTs. We show that the conventional requirement is overly restrictive and not necessary for a consistent UV-agnostic description. We then present the first dedicated phenomenological study of ALP EFTs in the complementary regime, focusing on the particularly clean case of leptophilic ALPs. Finally, we demonstrate that such a scenario can potentially alleviate the 3.8 $\sigma$ tension in the Caesium determination of the electron magnetic dipole moment.