CERN Accelerating science

Thesis
Report number	CERN-THESIS-2024-186
Title	Journey through the ALPs
Author(s)	Machado-Rodriguez, Jonathan (Madrid, Autonoma U.)
Publication	2024 - 185.
Thesis note	PhD : Madrid, Autonoma U. : 2024-07-16
Thesis supervisor(s)	Gavela, Belén ; Fernández de Trocóniz, Jorge
Note	Presented 04 Oct 2024
Subject category	Particle Physics - Phenomenology
Accelerator/Facility, Experiment	CERN LHC ; CMS
Abstract	The Standard Model (SM) of particle physics describes with exceptional accuracy almost everything we observe in the “visible” Universe. We know, however, that it is not the end of the story. There are major experimental phenomena which cannot be satisfactorily explained within the SM. Namely, dark matter (DM), dark energy, neutrino masses and the matter-antimatter asymmetry. These, together with the currently open theoretical questions concerning several of its free parameters —the hierarchy problem, the flavor puzzle and the strong-CP problem—, hint at some underlying unknown structure beyond the SM (BSM). This thesis is devoted to the phenomenology of axion-like particles (ALPs), hypo- thetical pseudo-Goldstone bosons (pGB) which are the telltale of hidden spontaneously broken global symmetries. The fact that (p)GBs have already been observed in Nature, in mesons and the longitudinal components of the electroweak gauge bosons, 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 the 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: vector boson scattering processes at the LHC mediated by a very off-shell or nonresonant ALP. 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 impact of ALP-neutrino effective interactions on the ALP couplings to the EW gauge boson. Using these results, we impose novel constraints on the ALP- neutrino parameter space recasting bounds 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 and shift-breaking interactions, and keeping track of mixing effects in the scalar sector. 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.

Corresponding record in: Inspire
Email contact: [email protected]