## Active neutrino

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Active neutrino is an alternative name for the Standard Model neutrino. It is sometimes convenient to call the usual, left-handed neutrinos active in contrast to sterile neutrinos, right-handed counterparts of the usual neutrinos. The main difference is that sterile neutrinos are not charged (singlets) with respect to all Standard Model gauge interactions. Strictly speaking, active neutrinos are charge eigen states. Indeed, neutrinos may be described as the mass eigen states, i.e. eigen states of the Hamiltonian defining the propagation of this particles, or as charge eigen states, i.e. the states having definite charges with respect to weak interactions of the Standard Model. Pure charge eigen states are created via weak interactions. Mass eigen state have definite propagation frequences. The fact that mass and charge operators do not commute for neutrinos is respoinsible for neutrino flavor oscillations.