Quark and gluon helicity evolution at small x : revised and updated
Cougoulic, F., Kovchegov, Y. V., Tarasov, A., & Tawabutr, Y. (2022). Quark and gluon helicity evolution at small x : revised and updated. Journal of High Energy Physics, 2022(7), Article 95. https://doi.org/10.1007/jhep07(2022)095
Julkaistu sarjassa
Journal of High Energy PhysicsPäivämäärä
2022Tekijänoikeudet
© The Authors. Article funded by SCOAP3
We revisit the problem of small Bjorken-x evolution of the gluon and flavor-singlet quark helicity distributions in the shock wave (s-channel) formalism. Earlier works on the subject in the same framework resulted in an evolution equation for the gluon field-strength F12 and quark "axial current" ψ¯γ+γ5ψ operators (sandwiched between the appropriate light-cone Wilson lines) in the double-logarithmic approximation (DLA: summing powers of αsln2(1/x) with αs the strong coupling constant). In this work, we observe that an important mixing of the above operators with another gluon operator, D←iDi, also sandwiched between the light-cone Wilson lines (with the repeated index i=1,2 summed over), was missing in the previous works. This operator has the physical meaning of the sub-eikonal (covariant) phase: its contribution to helicity evolution is shown to be proportional to another sub-eikonal operator, Di−D←i, which is related to the Jaffe-Manohar polarized gluon distribution. In this work we include this operator into small-x helicity evolution, and construct a novel evolution mixing all three operators (Di−D←i, F12, and ψ¯γ+γ5ψ), generalizing the previous results. We also construct closed DLA evolution equations in the large-Nc and large-Nc&Nf limits, with Nc and Nf the numbers of quark colors and flavors, respectively. Solving the large-Nc equations numerically we obtain the following small-x asymptotics of the quark and gluon helicity distributions ΔΣ and ΔG, along with the g1 structure function, ΔΣ(x,Q2)∼ΔG(x,Q2)∼g1(x,Q2)∼(1x)3.66αsNc2π√,
in complete agreement with the earlier work by Bartels, Ermolaev and Ryskin.
...
Julkaisija
Springer Science and Business Media LLCISSN Hae Julkaisufoorumista
1126-6708Julkaisu tutkimustietojärjestelmässä
https://converis.jyu.fi/converis/portal/detail/Publication/150878441
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Rahoittaja(t)
Euroopan komissio; Suomen AkatemiaRahoitusohjelmat(t)
Akatemiahanke, SA
The content of the publication reflects only the author’s view. The funder is not responsible for any use that may be made of the information it contains.
Lisätietoja rahoituksesta
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Award Number DE-SC0004286. The work of F.C. has been supported by the Academy of Finland, by the Centre of Excellence in Quark Matter and project 321840, and under the European Union’s Horizon 2020 research and innovation programme by the STRONG-2020 project (grant agreement No 824093) and by the European Research Council, grant agreement ERC-2015-CoG-681707. The content of this article does not reflect the official opinion of the European Union and responsibility for the information and views expressed therein lies entirely with the authors. ...Lisenssi
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