Kinetic mixing, custodial symmetry, $Z$, $Z^{\prime}$ interactions and $Z^{\prime}$ production in hadron colliders
In this work we study the interactions of the $Z$ and $Z^{\prime}$ generated by kinetic mixing in a class of theories for physics beyond the standard model motivated by the dark matter problem, containing a spontaneously broken extra $U(1)_{d}$ gauge factor group in a hidden scenario and a Higgs sector respecting custodial symmetry. It is shown that custodial symmetry allows us to write the $Z$ and $Z^{\prime}$ couplings to standard model fermions in terms of the measured values of $α$, $G_{F}$, $M_{Z}$ and $M_{Z^{\prime}}$. Working at the loop level, we calculate the ratio $ρ_{0}=M^{2}_{W}/\hat{c}^{2}_{Z}M^{2}_{Z}\hatρ$ used in the fit to electroweak precision data (EWPD) and use its value to estimate possible effects of kinetic mixing at the electroweak scale. For the $Z$ sector, we calculate the oblique parameters $S$ and $T$, finding that for $M_{Z^{\prime}}\geq M_{Z}$ our results are in agreement with the values of the oblique parameters extracted from the global fit to EWPD at $1σ$ level. As to the $Z^{\prime}$ sector, we calculate the $Z^{\prime}$ contributions to charged lepton pair production at the Large Hadron Colliderin the well motivated case of dark matter entering particle physics as the matter fields of the $U(1)_{d}$ gauge symmetry with perturbative couplings at the electroweak scale, finding that data reported by the Compact Muon Selenoid Collaboration impose a lower limit $M_{Z^{\prime}}\gtrsim 5.0 ~TeV$.