Dynamic chirality in the interacting boson model

The chiral interpretation of twin bands in odd-odd nuclei is investigated in the Interacting Boson Model framework. The analysis of the wave functions shows that the possibility for angular momenta of the valence proton, neutron and core to find themselves in the favorable, almost orthogonal geometry is present, but not dominant. Such behavior is found to be similar in nuclei where both the level energies and the electromagnetic decay properties display the chiral pattern, as well as in those where only the level energies of the corresponding levels in the twin bands are close together. The difference in the structure of the two types of chiral candidates nuclei can be attributed to different beta and gamma fluctuations, induced by the exchange boson-fermion interaction, i.e. by the antisymmetrization of odd fermions with the fermion structure of the bosons. In both cases the chirality is weak and dynamic. Among the nuclei that are candidates for chiral behavior, the best candidate is probably the odd-even Nd-135, where the beta and gamma fluctuations are strongly reduced and chirality, although dynamic in origin, is rather close to the static limit.