Theoretically (in the context of a polytropic-DM model) determined CMB-shift parameter, Eq. (111), as a function of the polytropic exponent −0.089 < Γ ≤ 0 (red solid line). The cyan horizontal straight line denotes the upper bound (at 68% CL) of the R-value, obtained from the nine-year WMAP survey final results, namely, R = 1.7387, and the corresponding green line denotes the mean value of R, arising from the combination of the Planck first-data release with those of the WMAP survey, namely, R = 1.7407. The vertical dashed lines denote the upper bound of Γ(| Γ | = 0.0271), arising from WMAP alone, and the corresponding most preferable value (| Γ | = 0.0398), arising from the combination of the Planck first-data release with those of the WMAP survey.