Theoretical constraints on new generations with and without Quarks or Neutrinos

TL;DR

This paper analyzes theoretical constraints on new fermion generations within extended Standard Model frameworks, showing that additional quark generations are incompatible with grand unification under current experimental bounds, and provides LHC search predictions.

Contribution

It offers a comprehensive theoretical analysis of chiral extensions of the Standard Model, specifically constraining new quark and lepton generations based on renormalization flows and experimental data.

Findings

Additional quark generations conflict with grand unification constraints.

Experimental bounds strongly limit the existence of new quark generations.

Predictions are made for LHC searches based on these constraints.

Abstract

We consider large classes of chiral extensions of the Standard Model, including new quark generations that do not involve additional neutrinos as well as lepton generations without quarks. An analysis of renormalization flows of Yukawa and quartic scalar couplings reveals that additional quarks are not compatible with a scenario of grand unification without violating the strong bounds from direct and Higgs searches at colliders. Constraints from direct searches, electroweak precision observables, and Higgs physics, together with the assumption that additional new physics beyond the extended chiral field content should enter significantly above the TeV scale, allows us to make predictions for searches at the LHC.