Evolution of the N=28 shell closure: a test bench for nuclear forces

The evolution of the N = 28 shell closure is investigated far from stability. Using the latest results obtained from various experimental techniques, we discuss the main properties of the N = 28 isotones, as well as those of the N = 27 and 29 isotones. Experimental results are compared with various theoretical predictions. These studies pinpoint the effects of several terms of the nucleon-nucleon interaction, such as the central, the spin-orbit (SO), the tensor and the three-body force components, to account for the modification of the N = 28 shell gap and SO splittings. Analogies between the evolution of the N = 28 shell closure and other magic numbers originating from the SO interaction are proposed (N = 14, 50 and 82). More generally, questions related to the evolution of nuclear forces towards the drip line, in bubble nuclei and for nuclei involved in the r-process nucleosynthesis are proposed and discussed.