Non-observable nature of the nuclear shell structure: meaning, illustrations and consequences

by Thomas Duguet (CEA Saclay)

Wednesday 6 May 2015, 14:30 → 15:30 Europe/Zurich

CERN

The concept of single-nucleon shells dates back to the early days of contemporary nuclear physics and constitutes the basic pillar of our understanding of nuclear structure. However, effective single-particle energies (ESPEs) are intrinsically theoretical quantities that "run" with the non-observable resolution scale s employed in the calculation (while true observables do not). A formal discussion will be provided to explain the difference between observable and non-observable quantities and the reasons why ESPEs, i.e. the shell structure, belongs to the latter category. State-of-the-art ab-initio calculations based on chiral two- and three-nucleon interactions will be employed to illustrate the situation. This will be done by comparing the behavior of observables and non-observable ESPEs under (quasi) unitary similarity renormalization group transformations of the Hamiltonian parameterized by the resolution scale s. The non-observable nature of the nuclear shell structure, i.e. the fact that it constitutes an intrinsically theoretical notion with no counterpart in the empirical world, must eventually be recognized and assimilated. Given that ESPEs do constitute a useful tool to interpret the behaviour of many-body observables in terms of simpler theoretical ingredients, the ultimate goal of the study is to specify the terms, i.e. the exact sense and conditions, in which this interpretation can be conducted meaningfully.