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. This allows for the phenomenon of neutrino oscillations, a flavour oscillation which is already known in other particle systems. The search for neutrino oscillations has to be performed in different ways: an appearance or disappearance mode. Matter effects can occur if the neutrinos under consideration experience different interactions by passing through matter. Having established neutrino oscillations, one of the major goals is to determine the PMNS matrix elements more precisely and search for a possible CP violation in the lepton sector. Obviously, this requires a full three-flavour analysis of all the available data. The expressions for the three-flavour oscillation probabilities including matter effects are quite complex.
