From Flavor Physics to Colliders: Realizing Quark-Lepton Unification at the TeV Scale

We propose an E₆-inspired Pati-Salam (PS) model that naturally accommodates TeV leptoquark gauge bosons, X_μ, through a softly broken Z₂ symmetry. In this setup, Standard Model fermions are Z₂ -even, while exotic fermions are Z₂ -odd. A distinctive feature is that the PS gauge bosons themselves are Z₂ -odd, so they couple only between ordinary and exotic fermions, except in the right-handed down sector, where soft Z₂ -breaking induces mixing. This arrangement suppresses meson decays at tree level, with noticeable effects showing up only at one loop. As a result, the PS breaking scale can be lowered while remaining consistent with meson oscillations and flavor-violating processes. Such a low-scale realization opens up exciting collider signatures, especially for discovering leptoquark gauge bosons and a unique signal of vector-like down-type quarks carrying a fractional baryon number of ± 2/3.