Speaker: Ionel Stetcu (Louisiana State University, Department of Physics and Astronomy)

Can we trust the random phase approximation?

Our understanding of nuclear structure is built upon mean-field theories such as Hartree-Fock and time-dependent Hartree-Fock.  The small-amplitude limit of the latter is the random phase approximation (RPA), which is widely used to model giant resonances in nuclei. Despite this popularity, RPA has been mostly validated against toy models; tests against complex models are scarce in the literature. We perform a thorough test of the RPA against full 0-hbar-omega shell model (SM) calculations. We allow deformed Hartree-Fock solutions and compare results for spherical and deformed nuclei.  We find reasonable agreement between RPA and SM, albeit with some significant failures. We also prove that a long-standing ``theorem" regarding RPA is violated in the case of deformation. Moreover, we bring evidence that the symmetries are only approximatively and unreliably restored.