Simple description of neutrinos in SU(5)

We show that experimental results for the masses and mixing of the neutrinos can be understood naturally by a simple grand unification model of SU(5) coupled to N=1 supergravity. No right-handed neutrinos are included. The left-handed neutrinos receive Majorana masses through the couplings with a Higgs boson of symmetric $\mathbf{15}$ representation. Introducing $\overline{\mathbf{45}}$ representation is optional for describing the masses of down-type quarks and charged leptons.