Journey through the ALPs

This thesis investigates the phenomenology of axion-like particles (ALPs), hypothetical pseudo-Goldstone bosons (pGB) which are the telltale of hidden spontaneously broken global symmetries. The fact that GBs and pGBs have already been observed in Nature, in the longitudinal components of the electroweak gauge bosons and pions, and the ubiquity of ALPs in a plethora of BSM extensions with a rich phenomenology across energies suggest that ALPs are ideal candidates to extend the SM particle content. We use the power of the model-independent effective field theory (EFT) framework throughout this thesis. The results presented here fall into two domains.

On one hand, this thesis explores the phenomenology of ALPs in high-energy collider searches. Specifically, we propose a powerful novel search window that takes advantage of the derivative nature of ALP interactions, to probe its couplings to the EW gauge bosons independently of the coupling to gluons.

On the other hand, the high-energy and high-precision era of experimental particle physics requires theoretical predictions to include radiative corrections. In this thesis, we study the one-loop connection between the ALP-neutrino and the ALP-EW gauge boson parameter spaces to impose novel constraints on ALP-neutrino couplings from collider data. 

Moreover, if a new scalar signal is detected at experiments, a compelling question to answer is whether this new particle is an ALP or not. Here we also present the full renormalization group equations (RGEs) of the SMEFT extended with a real scalar singlet up to dimension-five with one-loop accuracy, including CP-violating interactions. These results provide a useful tool for future phenomenological analyses targeting new physics signals in the scalar sector, allowing to pinpoint the differences between a generic scalar and a true ALP. The full set of RGEs of the singlet EFT are implemented in a new Mathematica package.

Supervisors: Belén Gavela and Jorge F. de Trocóniz