Renormalization scheme and gauge (in)dependence of the generalized Crewther relation: what are the real grounds of the $\beta$-factorization property?

Abstract

The scheme and gauge dependence of the factorization property of the RG $\beta$-function in the $SU(N_c)$ QCD generalized Crewther relation (GCR), which connects the non-singlet contributions to the Adler and Bjorken polarized sum rule functions, is investigated at the $\mathcal{O}(a_s^4)$ level. In the gauge-invariant $\overline{\mathrm{MS}}$-scheme this property holds at least at this order. To study whether this property is true in all gauge-invariant schemes, we consider the $\mathrm{MS}$-like schemes in QCD and the QED-limit of the GCR in the $\overline{\mathrm{MS}}$-scheme and in the $\mathrm{MOM}$ and the $\mathrm{OS}$ schemes. In these schemes we confirm the existence of the $\beta$-function factorization in the QCD and QED variants of the GCR. The problem of the possible $\beta$-factorization in the gauge-dependent renormalization schemes in QCD is studied. We consider the gauge non-invariant $\mathrm{mMOM}$ and $\mathrm{MOMgggg}$-schemes and demonstrate that in the $\mathrm{mMOM}$ scheme at the $\mathcal{O}(a_s^3)$ level the $\beta$-factorization is valid for three values of the gauge parameter $\xi$ only, namely for $\xi =-3,-1$ and $\xi =0$. In the $\mathcal{O}(a_s^4)$ order of PT it remains valid only for case of the Landau gauge $\xi =0$. The consideration of these two schemes for the QCD GCR allows us to conclude that the factorization of RG $\beta$-function will always be implemented in any $\mathrm{MOM}$-like schemes with linear covariant gauge at $\xi =0$ and $\xi =-3$ at the $\mathcal{O}(a_s^3)$ level. It is demonstrated that if factorization property for the $\mathrm{MS}$-like schemes is true in all orders of PT, as theoretically indicated, then the factorization will also occur in the arbitrary $\mathrm{MOM}$-like scheme in the Landau gauge in all orders of PT as well.

Comments: 45 pages; 1 Table