Coupling of pairing and triaxial shape vibrations in collective states of γ-soft nuclei

In addition to shape oscillations, low-energy excitation spectra of deformed nuclei are also influenced by pairing vibrations. The simultaneous description of these collective modes and their coupling has been a long-standing problem in nuclear structure theory. Here we address the problem in terms of self-consistent mean-field calculations of collective deformation-energy surfaces, and the framework of the interacting boson approximation. In addition to quadrupole shape vibrations and rotations, the explicit coupling to pairing vibrations is taken into account by a boson-number nonconserving Hamiltonian, specified by a choice of a universal density functional and pairing interaction. An illustrative calculation for $^{128}\mathrm{Xe}$ and $^{130}\mathrm{Xe}$ shows the importance of dynamical pairing degrees of freedom, especially for structures built on low-energy ${0}^{+}$ excited states, in $\ensuremath{\gamma}$-soft and triaxial nuclei.