Семинар «Теория квантового поля»

Дата и время: среда, 18 ноября 2020 г., в 11:00

Место: Онлайн конференция в Zoom, Лаборатория теоретической физики им. Н.Н. Боголюбова

Тема семинара: «The effects of higher corrections in perturbation theory in QCD and their theoretical features: the gauge dependence in the miniMOM-scheme and the character of the asymptotic behavior of PT series»

Докладчик: Виктор Молокоедов (ИЯИ, МФТИ)

Аннотация:

The dependence on the choice of renormalization schemes and the gauge parameter ξ of the Adler function for the process of e+e- annihilation into hadrons and of the coefficient function of the Bjorken sum rule for the deep-inelastic scattering of the charged leptons on polarized nucleons is investigated in the fourth-order of perturbation theory (PT). The gauge-invariant V-scheme, defined by the higher corrections to the static Coulomb QCD potential, and the gauge-non-invariant miniMOM-scheme of the momentum subtractions with explicit dependence on ξ are considered. A decline in the gauge dependence of the contributions of PT series for R-ratio with an increase in the number of radiation corrections taken into account from the 2-nd to the 4th order is demonstrated. The generalized Crewther relation, which involves the non-singlet flavor contributions to the Adler and Bjorken functions and is one of the manifestations of the effects of the conformal symmetry breaking in massless QCD, is studied. It is shown that the β-function included in this relation is factorized at least in the 4th order of PT in the class of the momentum subtraction schemes in the Landau gauge ξ=0. It is proved that the gauge invariance of the renormalization schemes is a sufficient but not necessary condition for the mentioned factorization. The asymptotic structure of the relation between the pole and the running MS-bar scheme masses of heavy quarks in QCD is studied. Using three different approaches to fixing the values of the still uncalculated higher-order PT contributions to this relation, their estimates are made in the 5th and 6th orders. It is concluded that for the t-quark the asymptotic nature of the considered relation does not still manifest itself even at the six-loop level. This fact serves as the argument in favour of the applicability of both its running and pole masses in modern theoretical studies. It is shown that all considered approximate methods (including a modern variant of the renormalon approach) lead to the sign-alternating coefficients of the investigated relation in terms of the number of massless quarks.