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QCD and strongly coupled gauge theories: challenges and perspectives

N. Brambilla, S. Eidelman, P. Foka, S. Gardner, A. S. Kronfeld, M. G. Alford, R. Alkofer, M. Butenschoen, T. D. Cohen, J. Erdmenger, L. Fabbietti, M. Faber, J. L. Goity, B. Ketzer, H. W. Lin, F. J. Llanes-Estrada, H. Meyer, P. Pakhlov, E. Pallante, M. I. Polikarpov, H. Sazdjian, A. Schmitt, W. M. Snow, A. Vairo, R. Vogt, A. Vuorinen, H. Wittig, P. Arnold, P. Christakoglou, P. Di Nezza, Z. Fodor, X. Garcia i Tormo, R. Höllwieser, A. Kalwait, D. Keane, E. Kiritsis, A. Mischke, R. Mizuk, G. Odyniec, K. Papadodimas, A. Pich, R. Pittau, Jian-Wei Qiu, G. Ricciardi, C. A. Salgado, K. Schwenzer, N. G. Stefanis, G. M. von Hippel, V. I . Zakharov

TL;DR

This comprehensive review delineates the status and challenges of QCD across light- and heavy-quark sectors, deconfinement, and dense nuclear matter. It synthesizes theoretical tools—lattice QCD, EFTs, and perturbative methods—with a broad spectrum of experimental inputs from colliders, fixed-targets, and heavy-ion facilities. The work highlights precise determinations of fundamental parameters, advances in hadron structure and spectroscopy, and the ongoing development of QCD-based descriptions of the quark-gluon plasma, confinement, and nuclear matter. It emphasizes the need for cross-disciplinary collaboration among theory and experiment to push precision tests of the SM, explore beyond-SM scenarios, and map the QCD phase diagram under extreme conditions. Overall, the document presents a vision for future progress through refined lattice calculations, improved EFTs, and new experimental programs at upcoming facilities.

Abstract

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly-coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

QCD and strongly coupled gauge theories: challenges and perspectives

TL;DR

This comprehensive review delineates the status and challenges of QCD across light- and heavy-quark sectors, deconfinement, and dense nuclear matter. It synthesizes theoretical tools—lattice QCD, EFTs, and perturbative methods—with a broad spectrum of experimental inputs from colliders, fixed-targets, and heavy-ion facilities. The work highlights precise determinations of fundamental parameters, advances in hadron structure and spectroscopy, and the ongoing development of QCD-based descriptions of the quark-gluon plasma, confinement, and nuclear matter. It emphasizes the need for cross-disciplinary collaboration among theory and experiment to push precision tests of the SM, explore beyond-SM scenarios, and map the QCD phase diagram under extreme conditions. Overall, the document presents a vision for future progress through refined lattice calculations, improved EFTs, and new experimental programs at upcoming facilities.

Abstract

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly-coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

Paper Structure

This paper contains 224 sections, 147 equations, 101 figures, 15 tables.

Table of Contents

  1. Overview
  2. Readers' guide
  3. The nature of QCD
  4. Broader themes in QCD
  5. Experiments addressing QCD
  6. Theoretical tools for QCD
  7. Effective Field Theories (EFTs):
  8. Lattice gauge theory:
  9. Other nonperturbative approaches:
  10. Fundamental parameters of QCD
  11. Light quarks
  12. Introduction
  13. Hadron structure
  14. Parton distribution functions in QCD
  15. PDFs in the DGLAP approach
  16. ...and 209 more sections

Figures (101)

  • Figure 1: Valence distribution of the pion obtained in Aicher:2010cb from a fit to the E615 Drell-Yan data Conway:1989fs at $Q=4$ GeV, compared to the NLO parameterizations of Sutton:1991ay Sutton-Martin-Roberts-Stirling (SMRS) and Gluck:1999xe Glück-Reya-Schienbein (GRS) and to the distribution obtained from Dyson-Schwinger equations by Hecht et al. Hecht:2000xa. From Aicher:2010cb.
  • Figure 2: Factorization for SIDIS of extra gluons into gauge links (double lines).Figure from Boer:2011fh.
  • Figure 3: (Upper figure) Gluon-gluon luminosity to produce a resonance of mass $M_X$ for different PDFs normalized to that of NNPDF2.3; (Lower figure) The corresponding uncertainties in the Higgs cross section from PDFs and $\alpha_s(M_Z)$. Figures from Ball:2012wy.
  • Figure 4: Fit using the NLO BK nonlinear evolution equations of the combined H1/ZEUS HERA data. Figure from Albacete:2010sy.
  • Figure 5: Connections among various partonic amplitudes in QCD. The abbreviations are explained in the text.
  • ...and 96 more figures