Such is the case for charged leptons, like the electron, but within the standard model the right-handed neutrino does not exist. So absent the sterile right chiral neutrinos to pair up with the left chiral neutrinos, even with Yukawa coupling the active neutrinos remain massless. In other words, there are no mass-generating terms for neutrinos under the Standard Model: For each generation, the model only contains a left-handed neutrino and its antiparticle, a right-handed antineutrino, each of which is produced in weak eigenstates during weak interactions; the "sterile" neutrinos are omitted. (See neutrino masses in the Standard Model for a detailed explanation.)