Triaxiality in the proton-neutron interacting boson model: Perturbed O(6) symmetry with application to the mass A≃130 Xe, Ba nuclei

In the present article, we discuss the Xe and Ba nuclei in the A≃130 mass region. This mass region has been shown to constitute a new region of O(6)-like nuclei. A number of deviations, however, from a pure O(6) dynamical symmetry are experimentally observed, in particular the energy staggering in the gamma band. Here, we study the influence of triaxial perturbations, i.e., introducing terms in the Hamiltonian that are of ${\mathrm{SU}}^{\mathrm{*}}$(3) type, on the energy spectra of the ${}_{}{}^{124\mathrm{-}130}{}_{}{}^{}\mathrm{Xe}$ and of the ${}_{}{}^{128\mathrm{-}134}{}_{}{}^{}\mathrm{Ba}$ nuclei. We also address the problem of B(E2) transitions, connecting the $2_{\gamma }^{+}$, $3_{\gamma }^{+}$, $4_{\gamma }^{+}$, $5_{\gamma }^{+}$, and $0_3^{+}$ levels to the ground state and the gamma band.