  Although the (varying power)-law modified gravity toy model has the
attractive feature of unifying the early and late-time expansions of the
Universe, thanks to the peculiar dependence of the scalar field's potential on
the scalar curvature, the model still suffers from the fine-tuning problem when
used to explain the actually observed Hubble parameter. Indeed, a more correct
estimate of the mass of the scalar field needed to comply with actual
observations gives an unnaturally small value. On the other hand, for a
massless scalar field the potential would have no minimum and hence the field
would always remain massless. What solves these issues are the radiative
corrections that modify the field's effective potential. These corrections
raise the field's effective mass rendering the model free from fine-tuning,
immune against positive fifth-force tests, and better suited to tackle the dark
matter sector.
