Resonance states in 12C and α-particle condensation

The states with Jπ = 0+, 2+, and 4+ of 12C with excitation energies less than about 15 MeV are investigated with the alpha condensate wave function with spatial deformation and by using the method of ACCC (analytic continuation in the coupling constant) which is necessary for a proper treatment of resonance states. The calculated energy and width of the recently observed 22+ state are found to be well reproduced. The obtained 22+ wave function has a large overlap with a single condensate wave function of 3α gas-like structure. The density distribution is shown to be almost the same as that of the 02+ state that is regarded as a 3α Bose-condensed state, if the energy of the 22+ state is scaled down to the same value as the one of the 02+ state. Furthermore, the kinetic energy, nuclear interaction energy, and Coulomb interaction energy of the calculated 22+ state are shown to be very similar to those of the 02+ state. We conclude that the 22+ state has a structure similar to the 02+ state of Bose-condensate character with a dilute 3α gas-like structure. In addition, the resonance states, 03+, 04+, 42+, are also discussed.