Parameters' domain in three flavour neutrino oscillations

We consider analytically the domain of the three mixing angles Theta (ij) a nd the CP phase delta for three flavour neutrino oscillations both in vacuu m and matter. Similarly to the quark sector, it is necessary and sufficient to let all the mixing angles Theta (12), Theta (13), Theta (23) and delta be in the range <0, pi /2 > and 0 less than or equal to delta < 2 pi, respe ctively. To exploit the full range of delta will be important in future whe n more precise fits are possible, even without CP violation measurements. W ith the above assumption on the angles we can restrict ourselves to the nat ural order of masses m(1) < m(2) < m(3). Considerations of the mass schemes with some negative deltam(2)'s, though for some reasons useful, are not ne cessary from the point of view of neutrino oscillation parametrization and cause double counting only. These conclusions are independent of matter eff ects. (C) 2001 Published by Elsevier Science B.V.