Adler function and Bjorken sum rule: generalizations of the Crewther relation in SU(Nc), the β-expansion of PT series, conformal symmetry limit and the way from PMC to the special extension of BLM approach

by Andrei Kataev (Institute for Nuclear Research of the Russian Academy of Science Moscow, Russia)

Tuesday 20 Dec 2016, 14:30 → 15:30 Europe/Madrid

IFAE Seminar room (IFAE)

The analytical QCD perturbation theory (PT) expressions for the general- ized Crewther relation, non-singlet contributions to the Adler function and the Bjorken sum rule for polarized lepton-nucleon scattering are considered in the case of SU(Nc) gauge theory. The relation to the {β}-expansion approach for the coefficients of the PT series is clarified. The special way of finding the ana- lytical form of the terms in the proposed by Mikhailov {β}-expansion pattern, is described. It avoids the necessity of introducing extra gluino degrees of free- dom, used in the concrete studies for technical reasons only. The comparisons between different {β}-expanded approximations for the Adler function and the Bjorken sum rule, including the ones, which follow from Brodsky- Wu-Mojaza PMC motivated expansion and Cvetic-Valenzuela skeleton motivated expansion, are presented. The scheme-independent relations between PT contributions to the Adler function and Bjorken sum rule, which are obtained in the conformal symmetry limit, are demonstrated. The considered by Kataev and Mikhailov (2015) proposal to transform PMC into the special extension the BLM approach is clarified.