“…However, other papers claimed that some of the models studied fail solar system tests [16] or at least under some conditions [17], but this has been contested in, for example, [18], and also in [19], where models that pass these tests were discussed. In addition to the phenomenology, it has been argued that the models have theoretical motivations within unification theories of fundamental interactions and within field quantization on curved space-times [23,24]. However, previous studies stressed that the models considered were chosen somewhat randomly due to the large spectrum of possible curvature invariants [4,20] and a systematic approach to these models is highly desirable [21,22].…”