ABSTRACT
In the case of a non-vanishing rest mass of the neutrino the weak and mass eigenstates are not necessarily identical, a fact well known in the quark sector where both types of states are connected by the CKM matrix (see section 3.3.2). This allows for the phenomenon of neutrino oscillations, a kind of flavour oscillation which is already known in other particle systems. It can be described by pure quantum mechanics. They are observable as long as the neutrino wave packets form a coherent superposition of states. Such oscillations among the different neutrino flavours do not conserve individual lepton numbers only total lepton number. We start with the most general case first, before turning to the more common two-and three-flavour scenarios. For additional literature see [Bil78, Bil87, Kay81, Kay89,Boe92, Kim93, Gro97, Sch97, Bil99, Lip99].
