  The treatment of intershell interactions remains a major challenge in the
theoretical description of strongly correlated materials. Most previous
approaches considered the influence of intershell interactions at best in a
static fashion, neglecting dynamic effects. In this work, we propose a
slave-rotor method that goes beyond this approximation by incorporating the
effect of intershell interactions in a dynamic manner. Our method is derived
and implemented as a quantum impurity solver in the context of dynamical mean
field theory and benchmarked on a two-orbital model system. The results from
our slave-rotor technique are found to be in good agreement with our reference
calculations that include intershell interactions explicitly. We identify and
analyze qualitative features emerging from the dynamic treatment. Our results
thus provide qualitatively new insights, revealing the ambivalent effect of
intershell interactions in strongly correlated materials.
