Realistic model for SU(5) grand unification

A grand unified model based on SU(5) and supersymmetry is presented. Pairs of superfields belonging to 15 and 15 representations are newly introduced, two pairs with even and one pair with odd matter parity. Improper mass relations in the minimal model between charged leptons and d-type quarks are corrected. Neutrinos have nonvanishing masses, with large angles for generation mixings of the leptons being compatible with the small angles of the quarks. A new source for lepton-number generation in the early universe is provided.