Examination of the inversion of isobaric analogue states in mirror nuclei

A recent study by Hoff and collaborators [Nature (London) 580, 52 (2020)] presented evidence that the ground-state spin of Sr-73 is different from that of its mirror, Br-73, likely due to an inversion of the ground- and first-excited states. Here, we assess the likelihood of such an inversion arising from normal isospin-symmetry breaking and, more broadly, whether such phenomena challenge our understanding of charge-symmetry-breaking forces in atomic nuclei. By placing the result within the context of previous experimental and theoretical work we demonstrate that this inversion lies entirely within the bounds of normal isospin-symmetry-breaking behavior. We further note that, in the context of isospin, neither level inversions nor the nuclear ground state hold any special significance.