Generator coordinate method for hypernuclear spectroscopy with a covariant density functional

We apply the generator coordinate method (GCM) to single-$\Lambda$ hypernuclei in order to discuss the spectra of hypernuclear low-lying states. To this end, we use the same relativistic point-coupling energy functional both for the mean-field and the beyond-mean-field calculations. This relativistic GCM approach provides a unified description of low-lying states in ordinary nuclei and in hypernuclei, and is thus suitable for studying the $\Lambda$ impurity effect. We carry out an illustrative calculation for the low-lying spectrum of $^{21}_\Lambda$Ne, in which the interplay between the hypernuclear collective excitations and the single-particle excitations of the unpaired $\Lambda$ hyperon is taken into account in a full microscopic manner.