The four-loop renormalization group QCD and QED $beta$-functions in the $V$-scheme and their analogy with the Gell-Mann--Low function in QED and QCD

The semi-analytical expression for the forth coefficient of the renormalization group $beta$-function in the ${rm{V}}$-scheme is obtained in the case of the $SU(N_c)$ gauge group. In the process of calculations we use the three-loop perturbative approximation for the QCD static potential, evaluated in the $rm{overline{MS}}$-scheme. The importance of getting more detailed expressions for the $n_f$-independent three-loop contribution to the static potential,obtained at present by two groups, is emphasised. The comparison of the numerical structure of the four-loop approximations for the RG $beta$- function of QCD in the gauge-independent ${rm{V}}$- and $rm{overline{MS}}$-schemes and in the minimal MOM scheme in the Landau gauge are presented. Considering the limit of QED with $N$-types of leptons we discover that the $beta^{rm{V}}$-function is starting to differ from the Gell-Mann--Low function $Psi(alpha_{rm{MOM}})$ at the level of the forth-order perturbative corrections, receiving the proportional to $N^2$ additional term. Taking this feature into account, we propose to consider the $beta^{rm{V}}$-function as the most theoretically substantiated analog of the Gell-Man--Low function in QCD.

Higgs Decay To bar{b}b: Different Approaches To Resummation Of QCD Effects

The comparison between parameterisations of the perturbation results for the decay width of the Standard Model Higgs boson to bar{b}b-quarks pairs, based on application of bar{MS}-scheme running quark mass and pole b-quark mass, are presented. In the case of the latter parameterisation taking into account of order O(alpha_s^3) term is rather important. It is minimising deviations of the results obtained at the O(alpha_s^2) level from the results, which follow from the running quark mass approach