Concerning pion parton distributions Cui, Z. F. Raya Montaño, Khépani We are grateful for constructive comments from K.-L. Cai, O. Denisov, F. de Soto, T. Frederico, J. Friedrich, C. Mezrag, V. Mokeev, W.-D. Nowak, C. Quintans, G. Salme and J. Segovia. Work supported by: National Natural Science Foundation of China (Grant nos. 12135007, 11805097); Helmholtz-Zentrum Dresden-Rossendorf High Potential Programme; Spanish Ministry of Science and Innovation (MICINN) (Grant nos. PID2020-113334GB, PID2019-107844GBC22); Generalitat Valenciana (Grant no. Prometeo/2019/087); Junta de Andalucia (Grant nos. P18-FR-5057, UHU-1264517, UHU EPIT2021); and STRONG-2020 "The strong interaction at the frontier of knowledge: fundamental research and applications" which received funding from the European Union's Horizon 2020 research and innovation programme (grant no. 824093). Analyses of the pion valence-quark distribution function (DF), u(pi) (x; sigma), which explicitly incorporate the behaviour of the pion wave function prescribed by quantum chromodynamics (QCD), predict u(pi) (x similar or equal to 1; sigma) similar to (1 - x)(beta(sigma)), beta(sigma greater than or similar to m(p)) > 2, where mp is the proton mass. Nevertheless, more than forty years after the first experiment to collect data suitable for extracting the x similar or equal to 1 behaviour of up, the empirical status remains uncertain because some methods used to fit existing data return a result for up that violates this constraint. Such disagreement entails one of the following conclusions: the analysis concerned is incomplete; not all data being considered are a true expression of qualities intrinsic to the pion; or QCD, as it is currently understood, is not the theory of strong interactions. New, precise data are necessary before a final conclusion is possible. In developing these positions, we exploit a single proposition, viz. there is an effective charge which defines an evolution scheme for parton DFs that is all-orders exact. This proposition has numerous corollaries, which can be used to test the character of any DF, whether fitted or calculated. 2022-02-07T11:30:57Z 2022-02-07T11:30:57Z 2022-01-24 info:eu-repo/semantics/article Cui, ZF... [et al.]. Concerning pion parton distributions. Eur. Phys. J. A 58, 10 (2022). [https://doi.org/10.1140/epja/s10050-021-00658-7] http://hdl.handle.net/10481/72695 10.1140/epja/s10050-021-00658-7 eng info:eu-repo/grantAgreement/EC/H2020/824093 http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Springer