Abstract
In spite of enormous experimental progress in determination of the neutrino
parameters, theory of neutrino mass and mixing is still on the cross-roads.
Guidelines could be (i) the connection between zero neutrino charges (and
therefore a possibility to be Majorana particle), smallness of the neutrino
mass and large lepton mixing, (ii) joint description of leptons and quarks,
(iii) existence of the right handed (RH) neutrinos without special quantum
numbers. Properties of the RH neutrinos and the UV completion of the seesaw may
turn out to be the key to understand the neutrino mass and mixing. In view of
the LHC results minimalistic scenarios like $\nu$MSM look rather plausible.
Still the GUT's with additional hidden sector, QLC, high scale flavor
symmetries are appealing. Concerning mixing, the main issue is "symmetry or no
symmetry" behind the observed pattern. The symmetry group condition is useful
tool to study consequences of symmetries and to perform "symmetry building".
Sterile neutrinos are challenge but also opportunity for the present
theoretical constructions.
