Structure of the Energy-Momentum Tensor and Applications

TL;DR

This paper reviews the fundamental role of the energy-momentum tensor in understanding nucleon structure, including spin decomposition, stress tensor insights, and applications to hadron spectroscopy like charmonium-nucleon pentaquarks.

Contribution

It provides a comprehensive overview of the energy-momentum tensor's structure and its applications in nucleon physics and hadron spectroscopy, highlighting recent progress.

Findings

Insights into nucleon spin decomposition and stress tensor structure.

Application of EMT to interpret charmonium-nucleon pentaquarks.

Recent progress in understanding strong force balance inside nucleons.

Abstract

The probably most fundamental information about a particle is contained in the matrix elements of its energy momentum tensor (EMT) which are accessible from hard-exclusive reactions via generalized parton distribution functions. The spin decomposition of the nucleon and Ji sum rule are one example. Less prominent but equally important information is encoded in the stress tensor, related to the spatial components of the EMT, which shows in detail how the strong forces inside the nucleon balance to form a bound state. This provides not only unique insights on nucleon structure. It also leads to fascinating new applications to hadron spectroscopy which allow us to formulate new interpretations of the charmonium-nucleon pentaquarks discovered by LHCb. Recent progress is reviewed in this short overview article.