Electroweak precision constraints on dark photon models with generalized mixing

We present a global fit to electroweak precision observables (EWPOs) in dark photon (DP) models containing both kinetic and mass mixing between the DP and the neutral gauge bosons of the Standard Model (SM). Such more general mixing can be the result of an extended scalar sector, which we specify in this paper. We calculate the tree-level contributions to EWPOs due to the mixing with the DP, as well as the leading loop corrections to the oblique parameters due to the extended Higgs sector. In the scalar sector, we find that ample regions of parameter space are still unconstrained by data. In the gauge sector, the excluded region depends strongly on the vacuum expectation values of the scalar fields: for moderate ratios, DP masses in the (40 GeV, 1 TeV) range are excluded; for larger ratios, the limits become indistinguishable from those for standard DPs.