A simple TeV-scale extension of the Standard Model by scalar leptoquarks recently gained popularity due to the flavor anomalies. But the non-observation of proton decay and charged lepton flavour violation severely constrain the leptoquark interactions, meaning that their ultraviolet (UV) realisation must be rather special. Using a lepton-flavored U(1)_X gauge symmetry to restrict the leptoquark interactions, we discover a novel mechanism for rendering the proton exactly stable to all orders in the effective field theory expansion. Introducing a scalar condensate to break the U(1)_X in the UV and generate realistic neutrino masses with a type-I seesaw leaves a linearly realised discrete Z_9 or Z_{18} gauge symmetry in the infrared (IR). This symmetry exactly prohibits all ΔB = 1 processes and can easily be adapted to many other new-physics models. Charged lepton flavour violation is forbidden at the renormalisable level, leaving the leptoquarks with approximately preserved muon number. We speculate that U(1)_X can emerge from a gauge-flavour unified theory with gauge group SU(12) x SU(2) x SU(2) even deeper in the UV.

The Standard Model Effective Field Theory (SMEFT) and the Low Energy Effective Field Theory (LEFT) can be extended by adding additional spin 0, 1/2 and 1 dark matter particles which are singlets under the Standard Model (SM) gauge group. We classify all gauge invariant interactions in the Lagrangian up to terms of dimension six, and present the tree-level matching conditions between the two theories at the electroweak scale. The most widely studied dark matter models, such as those based on the Higgs portal or on kinetic mixing between the photon and a dark photon, are based on dimension-four interactions with the SM sector. We consider a model with dark vector particles with a Z_2 symmetry, so that the lightest dark matter particle is stable. The leading interaction with the SM is through dimension-six operators involving two dark vector field-strength tensors and the electromagnetic field-strength tensor. This model is a viable dark matter model in the freeze-in scenario for a wide range of parameters.