Abstract
We propose a unified model of scalar particles that addresses the flavour hierarchies, solves the strong CP problem, delivers a dark matter candidate, and provides the trigger for electroweak symmetry breaking. Besides furnishing a unification of the recently proposed axiflavon with a Goldstone-Higgs sector, the scenario can also be seen as adding a model of flavour (and strong CP conservation along with axion dark matter) to elementary Goldstone-Higgs setups. In particular, we derive bounds on the axion decay constant from the need to generate a SM-like Higgs potential at low energies, which we confront with constraints from flavour physics and cosmology. In the minimal implementation, we find that the axion decay constant is restricted to a thin stripe of $f_a \approx (10^{11}-10^{12})$ GeV, while adding right-handed neutrinos allows to realize a heavy-axion model at lower energies, down to $f_a \sim 10$ TeV.
Highlights
The Standard Model (SM) of particle physics provides an excellent description of nature around the weak scale, it has several shortcomings that lead us to the conclusion that it is rather an effective low-energy parametrization of a more fundamental theory of nature
The apparent conservation of CP symmetry in strong interactions is in tension with in principle unsuppressed sources of CP violation in the QCD Lagrangian
The SM provides a successful parametrization of electroweak symmetry breaking (EWSB) via the Higgs mechanism, the origin of the Higgs potential is unknown
Summary
The Standard Model (SM) of particle physics provides an excellent description of nature around the weak scale, it has several shortcomings that lead us to the conclusion that it is rather an effective low-energy parametrization of a more fundamental theory of nature. The flavor hierarchies in the SM can be addressed via the Froggatt-Nielsen (FN) mechanism [1], i.e., by chirally charging the SM fermions under a Uð1ÞH flavor symmetry controlling their masses and mixings. Including the axiflavon can address fermion masses and mixings in these models, while providing a solution to the strong CP problem. This is a compelling renormalizable alternative to partial compositeness [21] generating flavor hierarchies in composite-Higgs models. In this way the flavor structure can be achieved without the need of adding a new disconnected scalar or a new symmetry-breaking mechanism. In two Appendices we discuss the assumptions regarding the mass spectrum of the FN messengers as well as the contributions from light fermions to the Higgs potential
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