Decomposed photon anomalous dimension in QCD and the {β} -expanded representations for the Adler function

This work is devoted to the study of the $\{\beta \}$ expansion of the perturbative expressions for the $e^{+}{e}^{-}$ annihilation Adler function $D(Q^2)$ and for the related renormalization group functions, namely, for the photon vacuum polarization function and its anomalous dimension $\gamma ({\alpha }_s)$ in QCD at the $\mathcal{O}({\alpha }_s^4)$ order. We emphasize that $\gamma ({\alpha }_s)$ is not a conformal-invariant contribution to $D(Q^2)$; therefore, for a consistent analysis, it is necessary to decompose its higher-order perturbation theory coefficients in powers of the $\beta$-function coefficients in the same way as for the Adler function. The arguments in favor of this statement are given. The comparison of the $\overline{\mathrm{MS}}$ and principal of maximum conformality and Brodsky-Lepage-Mackenzie scale approximants are demonstrated. We comment briefly on theoretical and phenomenologically related consequences of this comparison.