  The non-unitarity of the leptonic mixing matrix is a generic signal of new
physics aiming at the generation of the observed neutrino masses. We discuss
the Minimal Unitarity Violation (MUV) scheme, an effective field theory
framework which represents the class of extensions of the Standard Model (SM)
by heavy neutral leptons, and discuss the present bounds on the non-unitarity
parameters as well as estimates for the sensitivity of the Circular Electron
Positron Collider (CEPC), based on the performance parameters from the preCDR.
