  The microscopic justification of the emergence of SU(3) symmetry in heavy
nuclei remains an interesting problem. In the past, the pseudo-SU(3) approach
has been used, with considerable success. Recent results seem to suggest that
the key for understanding the emergence of SU(3) symmetry lies in the
properties of the proton-neutron interaction, namely in the formation of (S=1,
T=0) p-n pairs in heavy nuclei, especially when the numbers of valence protons
and valence neutrons are nearly equal. Although this idea has been around for
many years, since the introduction of the Federman-Pittel mechanism, it is only
recently that information about the p-n interaction could be obtained from
nuclear masses, which become available from modern facilities. Based on this
information, a new coupling scheme for heavy deformed nuclei has been suggested
and is under development.
