Exploring Abelian-Non-Abelian Kinetic Mixing in SMEFT and Beyond

We explore a novel scenario involving Abelian-non-Abelian kinetic mixing within the framework of the Standard Model Effective Field Theory (SMEFT) and its extension with a real triplet scalar field. In SMEFT, this mixing arises exclusively from a dimension-6 operator involving the Standard Model Higgs doublet, while the real triplet scalar field introduces an additional dimension-5 operator. We derive the modifications to electroweak gauge boson properties and impose constraints using electroweak precision data. In SMEFT, we find that $Z$ pole data at LEP-I imposes a stringent constraint on the kinetic mixing parameter, requiring it to be less than $O$($10^{-4}$), which corresponds to a new physics scale of about 10 TeV. In the SMEFT+triplet scenario, the constraint can be significantly relaxed with a sizeable triplet vacuum expectation value while preserving custodial symmetry in a finely-tuned parameter space. Future measurements from the Circular Electron Positron Collider could probe the kinetic mixing parameter down to an order of magnitude smaller.