On the application of symmetry breaking and its restoration to treat   pairing correlation in finite nuclei
  An alternative approach to symmetry restoration within Energy Density Functional, the Symmetry-Conserving EDF is discussed. In this approach, the energy is directly written in terms of the degrees of freedom encoded in the one-, two-... body density matrices of the state having good quantum numbers. The SC-EDF framework is illustrated within Projection After and Before variation applied to particle number restoration. 
Guillaume Hupin and Denis Lacroix
nucl-th