Global investigation of differential mean-square charge radii in covariant density functional theory.*

A systematic global investigation of differential charge radii has been performed within the CDFT

framework for the first time. Theoretical results obtained with conventional covariant energy density

functionals and separable pairing interaction are compared with experimental differential

charge radii in the regions of the nuclear chart in which available experimental data crosses neutron

shell closures at N = 28; 50; 82 and 126. The analysis of absolute differential radii of different isotopic

chains and their relative properties indicate clearly that such properties are reasonably well described

in model calculations in the cases when the mean-field approximation is justified. However, while

the observed clusterization of differential charge radii of different isotopic chains is well described

above the N = 50 and N = 126 shell closures.

It is shown that the kinks in the charge radii at neutron shell closures are due to the underlying single-particle structure and due to weakening or collapse of pairing at

these closures. The regions of the nuclear chart in which the correlations beyond mean-field are

expected to have an impact on charge radii are indicated; the analysis shows that the assignment

of a calculated excited prolate minimum to the experimental ground state allows to understand

the trends of the evolution of di erential charge radii with neutron number in many cases of shape

coexistence even at the mean- field level. It is usually assumed that pairing is a dominant contributor

to odd-even staggering (OES) in charge radii. Our analysis paints a more complicated picture. It

suggests a new mechanism in which the fragmentation of the single-particle content of the ground

state in odd-mass nuclei due to particle-vibration coupling provides a signi cant contribution to

OES in charge radii.