Shape mixing in 0 nu beta beta candidates

Weak processes are typically observed through nuclear effects, as they mediate between different eigenstates of either one nucleus, or a pair of nuclei. Since the derivation of important parameters of the weak interaction and weakly-interacting particles, such as their masses, spin dependencies, and alike, heavily relies on nuclear theory, it must be assured that theory properly describes the relevant wave functions. A special challenge for neutrinoless double-beta decay, for example, is the location of many candidate isotopes in regions of the nuclear chart, where nuclei may exist simultaneously in different shapes, hence, different wave function components belonging to different nuclear deformations mixing into the nuclear eigenstates. In addition, isovector parameters of nuclear models are not often well constrained, posing an additional challenge. Through the measurement of properties of the nuclear scissors mode, a magnetic isovector excitation at low energies, using photon-scattering techniques, we obtain data that is relevant to constrain the structure of the nuclei and their eigenstates in question. Furthermore, our recent research program comprises the investigation of isotopes relevant for the detection of hypothetical massive weakly-interacting particles.