Possible shape coexistence in odd-ANe isotopes and the impurity effects of Λ hyperons

Abstract：

In this study, shape evolution and possible shape coexistence are explored in odd- ANe isotopes in the framework of the multidimensionally constrained relativistic-mean-field (MDC-RMF) model. By introducing $ s_\Lambda $ and $ p_{\Lambda} $ hyperons, the impurity effects on the nuclear shape, energy, size, and density distribution are investigated. For the $ NN $ interaction, the PK1 parameter set is adopted, and for the $ \Lambda N $ interaction, the PK1-Y1 parameter set is used. The nuclear ground state and low-lying excited states are determined by blocking the unpaired odd neutron in different orbitals around the Fermi surface. Moreover, the potential energy curves (PECs), quadrupole deformations, nuclear r.m.s. radii, binding energies, and density distributions for the core nuclei as well as the corresponding hypernuclei are analyzed. By examining the PECs, possibilities for shape coexistence in $ ^{27,29} $ Ne and a triple shape coexistence in ³¹Ne are found. In terms of the impurity effects of Λ hyperons, as noted for even-even Ne hypernuclear isotopes, the $ s_{\Lambda} $ hyperon exhibits a clear shrinkage effect, which reduces the nuclear size and results in a more spherical nuclear shape. The $ p_{\Lambda} $ hyperon occupying the $ 1/2^-[110] $ orbital is prolate, which causes the nuclear shape to be more prolate, and the $ p_{\Lambda} $ hyperon occupying the $ 3/2^-[101] $ orbital displays an oblate shape, which drives the nuclei to be more oblate.