Local versus nonlocal αα interactions in a 3α description of 12C

Local alpha alpha potentials reproducing the alpha alpha phase shifts fail to describe C-12 as a 3 alpha system. Nonlocal alpha alpha potentials that renormalize the energy-dependent kernel of the resonating group method allow interpreting simultaneously the ground state and 0(2)(+) resonance of C-12 as 3 alpha states. A comparison with fully microscopic calculations provides a measure of the importance of three-cluster exchanges in those states. (c) 2007 Elsevier B.V. All rights reserved.