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This comment regards a central aspect of the referred-to paper, the issue ofconvergence of the large coordination-number expansion. Perturbation expansionsof expressions containing a large number of parameters are generally invaliddue to the non-analyticity of the expanded expressions. I refer to recent workwhere these issues are analyzed and discussed in detail in relation to abenchmark example of a cluster model. As discussed therein, methods which areuncontrollable and for which their convergence is not foreseeable are not onlyuseless but can mislead, particularly if models derived from them are used tointerpret experiments.

Comment on the paper "Quasi-particle approach for lattice Hamiltonians  with large coordination numbers" by P. Navez, F. Queisser and R. Sch\"utzhold  - J. Phys. A: Math. Theor. 47 225004 (2014)