γZKinetic Mixing as Signal of a Higher Scale

In models with an additional large scale the low-energy effective Lagrangian may contain terms beyond the standard model which generate kinetic mixing between the $\gamma$ and $Z$. This modifies the coupling of the $Z$ and changes the relation between the masses of the $W$ and $Z$ and the parameters ${\alpha }_{\mathrm{EM}}$, $G_{\mathrm{F}}$, and ${sin\theta }_w^2$. Such an effect, which probes the existence of a higher scale (compositeness, extended hypercolor, etc.) may be seen in future precision measurements of the $W$ and $Z$ masses and $Z$ couplings.