Theoretical perspective for the future experiments on parton densities

TL;DR

This paper reviews the current status and future prospects of parton distribution function studies, including unpolarized, nuclear, polarized PDFs, and 3D structure functions, highlighting their importance in understanding nucleon structure and related phenomena.

Contribution

It provides a comprehensive overview of the current PDF research landscape and discusses future experimental directions and the potential of 3D structure functions in nucleon physics.

Findings

Unpolarized PDFs are a precision QCD field with higher-order corrections.

3D structure functions relate to nucleon spin and mass origins.

Future experiments will advance understanding of hadron internal structure.

Abstract

I explain the current status of parton-distribution-function (PDF) studies and future experimental prospects on their determinations. First, unpolarized PDFs of the nucleon are introduced as a field of precision QCD physics including higher-order $\alpha_s$ corrections. Second, nuclear PDFs and polarized nucleonic PDFs are discussed. Third, the determination of fragmentation functions is explained. Forth, the three-dimensional (3D) structure functions are discussed in connection with the origin of the nucleon spin and gravitational form factors of hadrons. By the 3D structure functions, gravitational sources and the origin of nucleon mass could be clarified in the microscopic level of quarks and gluons. Furthermore, 3D structure studies of hadrons could be used for clarifying internal structure of exotic hadron candidates, nuclear composition of ultra-high-energy cosmic rays, and color-entanglement phenomena. The PDF field will be developed further along with progress in other fields of science.