A complex integration technique to remove spurious states associated with spontaneously broken symmetries in RPA calculations

The removal of the spurious states associated with the violation of rotational and gauge invariance by mean field approximation from the RPA solutions describing the low-energy spectrum of nuclei is a notoriously difficult task, in particular in a rotating frame. A novel, numerically accurate yet technically simple method to accomplish this aim has been developed based on linear response theory. The results of calculations carried out for the deformed, superfluid, rotating nucleus ¹⁶⁸Yb testify to the power of the technique, the associated solutions respecting the variety of sum rules required to be fulfilled by the RPA solutions because of conservation laws.