# Quadrupole forces between quark/gluon subsystems inside higher-spin particles

## TL;DR

This paper extends the mechanical interpretation of forces between quark and gluon subsystems from nucleons to higher-spin particles, clarifying the role of energy-momentum tensor form factors through multipole expansion.

## Contribution

It introduces a multipole expansion approach to interpret non-conserved EMT form factors for higher-spin particles, advancing understanding of internal forces in these systems.

## Key findings

- Identifies meaningful combinations of EMT form factors for higher-spin particles.
- Provides a clear mechanical interpretation of these form factors.
- Extends previous nucleon-focused models to arbitrary higher-spin particles.

## Abstract

We generalize the mechanical interpretation of the forces between quark and gluon subsystems, previously studied for the nucleon, to arbitrary higher-spin particles. For spin-0 and spin-1/2 particles, this force is characterized by the non-conserved $\bar{c}(t)$ form factor. However, such an interpretation has not yet been established for higher-spin particles due to the intricate structure of the non-conserved energy-momentum tensor (EMT) form factors. By performing a multipole expansion, we identify the physically meaningful combinations of the non-conserved covariant EMT form factors and provide them with a clear mechanical interpretation.