We perform a detailed study of lepton mixing patterns arising from a scenario with three Majorana neutrinos in which a discrete flavor group G f = (3n 2 ) or G f = (6n 2 ) and a CP symmetry are broken to residual symmetries G e = Z 3 and G ν = Z 2 × CP in the charged lepton and neutrino sectors, respectively. While we consider all possible Z 3 and Z 2 generating elements, we focus on a certain set of CP transformations. The resulting lepton mixing depends on group theoretical indices and one continuous parameter. In order to study the mixing patterns comprehensively for all admitted G e and G ν , it is sufficient to discuss only three types of combinations. One of them requires as flavor group (6n 2 ). Two types of combinations lead to mixing patterns with a trimaximal column, while the third one allows for a much richer structure. For the first type of combinations the Dirac phase as well as one of the Majorana phases are trivial, whereas the other two types of combinations predict in general all CP phases to be non-trivial and also non-maximal. Already for small values of the index n of the group, n ≤ 11, experimental data on lepton mixing can be accommodated well for particular choices of the parameters of the theory. We also comment on the relation of the used CP transformations to the automorphisms of (3n 2 ) and (6n 2 ).

We consider the possibility of several different mechanisms contributing to the (ββ)0ν -decay amplitude in the general case of CP nonconservation: light Majorana neutrino exchange, heavy left-handed (LH) and heavy right-handed (RH) Majorana neutrino exchanges, lepton charge nonconserving couplings in SUSY theories with R-parity breaking. If the (ββ)0ν -decay is induced by, e.g., two "non-interfering" mechanisms (light Majorana neutrino and heavy RH Majorana neutrino exchanges), one can determine |ηi| 2 and |ηj | 2 , ηi and ηj being the two fundamental parameters characterising these mechanisms, from data on the half-lives of two nuclear isotopes. In the case when two "interfering" mechanisms are responsible for the (ββ)0ν -decay, |ηi| 2 and |ηj | 2 and the interference term can be uniquely determined, in principle, from data on the half-lives of three nuclei. Given the half-life of one isotope, the "positivity conditions" |ηi| 2 ≥ 0 and |ηj | 2 ≥ 0 lead to stringent constraints on the half-lives of the other (ββ)0ν -decaying isotopes. These conditions, as well as the conditions for constructive (destructive) interference are derived and their implications are analysed in two specific cases. The experimental limits on neutrino masses obtained in the 3 H β-decay experiments can constrain further the multiple mechanisms of (ββ)0ν -decay if one of the mechanisms involved is the light Majorana neutrino exchange. The measurements of the half-lives with rather high precision and the knowledge of the relevant nuclear matrix elements with relatively small uncertainties is crucial for establishing that more than one mechanisms are operative in (ββ)0ν -decay. The method considered by us can be generalised to the case of more than two (ββ)0ν -decay mechanisms. It allows to treat the cases of CP conserving and CP nonconserving couplings generating the (ββ)0ν -decay in a unique way.

We present a SUSY SUð5Þ Â T 0 unified flavor model with type I seesaw mechanism of neutrino mass generation, which predicts the reactor neutrino angle to be 13 % 0:14 close to the recent results from the Daya Bay and RENO experiments. The model predicts also values of the solar and atmospheric neutrino mixing angles, which are compatible with the existing data. The T 0 breaking leads to tribimaximal mixing in the neutrino sector, which is perturbed by sizeable corrections from the charged lepton sector. The model exhibits geometrical CP violation, where all complex phases have their origin from the complex Clebsch-Gordan coefficients of T 0 . The values of the Dirac and Majorana CP violating phases are predicted. For the Dirac phase in the standard parametrization of the neutrino mixing matrix we get a value close to 90 : ffi =2 À 0:45 c ffi 84:3 , c being the Cabibbo angle. The neutrino mass spectrum can be with normal ordering (2 cases) or inverted ordering. In each case the values of the three light neutrino masses are predicted with relatively small uncertainties, which allows one to get also unambiguous predictions for the neutrinoless double beta decay effective Majorana mass.