Renormalization group evolution of the non-unitary operator

Integrating out a heavy field gives rise to effective Lagrangian containing higher-dimensional operators. In the context of Type-I seesaw mechanism, integrating out the heavy right-handed neutrino field leads to unique dimension-five operator which gives the tree level neutrino mass term. Apart from these there are dimension-six operators that can have important implications. A linear combination of two such operators gives rise to the non-unitarity in the lepton mixing matrix, _UPMNS$U_{\mathrm{PMNS}}$. In this paper, we discuss the origin of non-unitarity at the high scale and its evolution through renormalization group running.