1. M Gell-Mann, P Ramond and R Slansky Supergravity, Proceeding of the Workshop, Stony Brook, New York, (1979); R N Mahapatra and G Senjanovic Phys. Rev. Lett. 44 912 (1980)
2. S Davidson, E Nardi, Yosef, arXiv:0802.2962 and further references threin
3. A D Sakharov JETP Lett. 5 24 (1967)
4. V A Kuzmin, V A Rubakov, M E Shaposhnikov Phys. Lett. 155B 36 (1985)
5. M Fukugita and T Yanagida Phys. Lett. 174B 45 (1986)