Fractals, nonextensive statistics, and QCD

In this work, we analyze how scaling properties of Yang-Mills field theory manifest as self-similarity of truncated n-point functions by scale evolution. The presence of such structures, which actually behave as fractals, allows for recurrent nonperturbative calculation of any vertex. Some general properties are indeed independent of the perturbative order, what simplifies the nonperturbative calculations. We show that for sufficiently high perturbative orders a statistical approach can be used, the nonextensive statistics is obtained, and the Tsallis index, q, is deduced in terms of the field theory parameters. The results are applied to QCD in the one-loop approximation, where q can be calculated, resulting in a good agreement with the value obtained experimentally. We discuss how this approach allows us to understand some intriguing experimental findings in high energy collisions, as the behavior of multiplicity against collision energy, long-tail distributions, and the fractal dimension observed in intermittency analysisA. D. and D. P. M. are partially supported by the Conselho Nacional de Desenvolvimento Cientfico e Tecnolgico (CNPq-Brazil) and by Project INCTFNA Proc. No. 464898/2014-5. A. D. is partially supported by FAPESP under Grant No. 2016/17612-7. The work of E. M. is supported by the Spanish MINEICO and European FEDER funds under Grants No. FIS2014-59386-P and No. FIS2017-85053-C2-1-P, by the Junta de Andalucía under Grant No. FQM-225, and by the Consejería de Conocimiento, Investigación y Universidad of the Junta de Andalucía and European Regional Development Fund Grant No. SOMM17/6105/UGR. The research of E. M. is also supported by the Ramón y Cajal Program of the Spanish MINEICO under Grant No. RYC-2016-20678