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Contenuto archiviato il 2024-05-29

Minimal grand unified theory

Final Activity Report Summary - MUST (Minimal Grand Unified Theory)

Grand Unified Theories of elementary particle physics have been around for more than three decades. They represent natural extension of the current paradigm of elementary particle physics, i.e. the so-called Standard Model, aiming at providing unifying picture for fundamental interactions and all elementary particles that participate in them. In their quest they automatically address some of the conceptual issues of the Standard Model by reproducing correct charge assignment of elementary particles and explaining anomaly cancellation. Enhanced further by super-symmetry-the space-time symmetry linking bosons and fermions-they represents a robust setup well-adjusted for elementary particle model builders.

The super-symmetric re-normalisable SO(10) Grand Unified Theory with three generations of matter fields and the Higgs representations comprising one 210-dimensional representation, two 126-dimensional representations, and one 10-dimensional representation has 26 free parameters. It is thus considered to be the minimal re-normalisable Grand Unified Theory. Furthermore, this theory relates the masses and mixing parameters in the charged fermion sector with those in the neutrino sector through use of 15 parameters only. Experiments, on the other hand, have already measured 17 out of total of 22 physical quantities in these two sectors with sufficiently good accuracy. Clearly, the theory must make 17 (post)dictions and 5 predictions with only 15 parameters if it is to be viable.

All previous attempts in literature to fit fermion sector consistently within the framework of the minimal re-normalisable Grand Unified Theory have not been successful. However, these studies have been assumption driven and were thus probing only a limited region of the available parameter space.

Our main objective was to perform the very first self-consistent analysis of the minimal re-normalisable Grand Unified Theory. We have successfully accomplish just that. Moreover, we have found a good fit of the fermion masses and their mixing parameters. Our solution requires a multistep SO(10) breaking within the so-called split super-symmetry scenario. It further predicts rather low unification scale that will be probed in experiments dedicated to proton decay searches due to a fast proton decay through the so-called d=6 operators of the SO(10) type. It also predicts at most gauginos and higgsinos at Large Hadron Collider.