Electroweak-flavour and quark-lepton unification: a family non-universal path

TL;DR

This paper proposes a family-non-universal extension of the Standard Model with a specific gauge group structure, explaining fermion mass hierarchies and suppressing flavor-changing processes, with testable predictions at TeV scales.

Contribution

It introduces a novel gauge symmetry breaking chain that unifies electroweak and flavor symmetries differently for the first two and third fermion families, providing new insights into fermion hierarchies and collider phenomenology.

Findings

Hierarchical fermion masses explained by staggered symmetry breaking.

Suppressed flavor-changing processes for the first two generations.

TeV-scale 4321 symmetry-breaking with distinctive collider signatures.

Abstract

We present a family-non-universal extension of the Standard Model where the the first two families feature both quark-lepton and electroweak-flavour unification, via the $SU(4) \times Sp(4)_L \times Sp(4)_R$ gauge group, whereas quark-lepton unification for the third family is realised \`a la Pati-Salam. Via staggered symmetry breaking steps, this construction offers a natural explanation for the observed hierarchical pattern of fermion masses and mixings, while providing a natural suppression for flavour-changing processes involving the first two generations. The last-but-one step in the symmetry-breaking chain is a non-universal 4321 model, characterised by a vector leptoquark naturally coupled mainly to the third generation. The stability of the Higgs sector points to a 4321$\to$SM symmetry-breaking scale around the TeV, with interesting phenomenological consequences in $B$ physics and collider processes that differ from those of other known 4321 completions.