Are there classical (ie. non-quantum) theories with inaccessible coupling regions, which can be shown to exist from extrapolating their RG flows derived from weak coupling ranges? Since these intermediate coupling ranges can neither be studied through weakly perturbing exact theories nor through effective theories of bound states, how else are they studied?
Background: For quantum systems like quantum phase transitions, QCD etc, much has been written about inaccessible coupling ranges (especially the intermediate coupling regions in BCS->BEC, quark->hadron etc where neither small coupling perturbation nor large coupling effective theories apply). These regions are indirectly shown to exist through extrapolating RG flow equation derived for weak coupling ranges. I want to know if such phases have been known to exist in non-quantum systems.
PS: I had asked a similar question (which is still open/unaswered), but that was purely in the context of classical turbulence: Similarities between laminar-turbulence transition and others like BCS-BEC crossover, quark-hadron transition etc