Nuclear shapes in covariant density functional theory: recent results

One of the most interesting questions of nuclear structure is the existence of different nuclear shapes and their evolution with particle number and spin. In particular, a special attention is attracted to 'exotic' ones, namely, the types of nuclear shapes which have not been studied extensively (or at all) in experiment. In my presentation I will focus on recent results obtained within the covariant density functional theory (CDFT) which are related to the investigation of such shapes. First, I will present the results of global studies of octupole deformation. A new region of octupole deformation, centered around Z ∼ 98, N ∼ 196 is predicted for the first time. This region plays an important role in fission recycling in the mergers of neutron stars. In terms of its size in the (Z, N) plane and the impact of octupole deformation on binding energies this region is similar to the best known region of octupole deformed nuclei centered at Z ∼ 90, N ∼136. For the latter island of octupole deformed nuclei, the calculations suggest substantial increase of its size as compared with available experimental data. Then, I will discuss the presence of large oblate deformations in superheavy nuclei. It is interesting that some well tested covariant energy density functionals predict only very few spherical super-heavy nuclei above Z = 110 and N = 172; the oblate ground states dominate the nuclear landscape here. Such an absence of 'magic' spherical super-heavy nuclei has never been discussed before and it is a consequence of the competition of the shell effects at spherical and oblate shapes. Note that in those two investigations we pay special attention to the assessment of the accuracy of the description of existing experimental data and theoretical uncertainties for the prediction of the properties of unknown nuclei. Finally, I will discuss super-, hyper- (HD) and mega-deformed (MD) shapes and clusterization in the N ≅ Z, A ∼ 40 mass region. Here, the rotation acts as a tool to bring these exotic shapes to the yrast line or its vicinity so that their observation becomes feasible with future generation of γ-tracking (or similar) detectors. The observation of the HD and MD structures at spin zero is basically impossible because they are located at high excitation energy with respect of the ground state. For several nuclei in this study (such as ³⁶Ar), the addition of several spin units above currently measured maximum spin of 16^- will inevitably trigger the transition to the HD and MD shapes. This document is composed of an abstract and the slides of the presentation. (authors)