Shell Evolution in Exotic Nuclei

The evolution of shell structure and the consequent variation of the magic numbers are discussed for exotic nuclei. A major origin of the shell evolution is shown to be the spin-isospin dependent central part of the nucleon-nucleon interaction in nuclei. The importance and robustness of this mechanism is shown in connection to the τ · τ σ · σ interaction. In neutron-rich exotic nuclei, magic numbers such as N=8, 20, etc. can disappear, while N=6, 16, etc. arise. The τ · τ σ · σ interaction should be related to Gamov-Teller and magnetic properties. Another mechanism of the shell evolution is shown to be the tensor interaction.