  The discovery of spontaneous symmetry breaking in particle physics was the
greatest contribution in Nambu's achievements. There is another class of
symmetries that exist in the low energy nature, yet is doomed to be broken at
high energy, due to a lack of protection of the gauge symmetry. I shall review
our approach to search for this class of symmetry breaking, the lepton number
violation linked to generation of the matter-antimatter asymmetry in our
universe.
