(Almost) Everything is a Dicke model -- Mapping non-superradiant correlated light-matter systems to the exactly solvable Dicke model

We investigate classes of interacting quantum spin systems in a single-mode cavity with a Dicke coupling, as a paradigmatic example of strongly correlated light-matter systems. Coming from the limit of weak light-matter couplings and large number of matter entities, we map the relevant low-energy sector of a broad class of models in the non-superradiant phases onto the exactly solvable Dicke model. We apply the outcomes to the Dicke-Ising model as a paradigmatic example, in agreement with results obtained by mean-field theory. We further accompany and verify our findings with finite-size calculations, using exact diagonalization and the series expansion method pcst++.