Twin Pati-Salam theory of flavour for a new picture of $B$-anomalies

Abstract: We discuss a theory of flavour which can simultaneously explain and connect the origin of the Standard Model flavour hierarchies with the $U_{1}(\mathbf{3},\mathrm{\mathbf{1},2/3})$ leptoquark explanation of the $B$-decay flavour anomalies. First, we motivate the vector leptoquark $U_{1}$ as an excellent mediator to address the updated picture of $B$-anomalies. Secondly, we introduce the Twin Pati-Salam theory of flavour, which naturally provides a low scale 4321 gauge group with a TeV scale $U_{1}$. We show that both the couplings of $U_{1}$ to SM fermions and the effective SM Yukawa couplings arise from the same physics, naturally providing a pattern of dominantly left-handed $U_{1}$ couplings as most preferred by current data. Finally, we discuss the most promising signals at low energy processes that can test the model in the near future.