The excitation spectra of ${}_{\mathrm{\Lambda }}{}^{27}\mathrm{Mg}$ as well as ${}^{26}\mathrm{Mg}$ are investigated within the framework of antisymmetrized molecular dynamics. In ${}^{26}\mathrm{Mg}$, it is found that the ground ($K^{\pi }=0^{+}$) and side ($K^{\pi }=2^{+}$) bands exhibit triaxial deformation. In addition to these bands, I also obtain three positive-parity bands with different nuclear quadrupole deformations in ${}^{26}\mathrm{Mg}$, whose energies and transition probabilities are consistent with observations. In ${}_{\mathrm{\Lambda }}{}^{27}\mathrm{Mg}$, five bands are predicted by the addition of a $\mathrm{\Lambda }$ particle in $s$ wave, corresponding to those in ${}^{26}\mathrm{Mg}$. In contrast, the coupling of a $\mathrm{\Lambda }$ particle in $p$ wave to the positive-parity states in ${}^{26}\mathrm{Mg}$ gives rise to a large number of excited states. These states can be classified into three groups having different spatial distributions of the $\mathrm{\Lambda }$ particle due to the triaxial deformation of the core nucleus ${}^{26}\mathrm{Mg}$.

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• Hypernuclei & mesic nuclei
• Nuclear structure & decays
• 20 ≤ A ≤ 38
• Nuclear many-body theory