On the Origin of Model Relations among Transverse-Momentum Dependent Parton Distributions

TL;DR

This paper reviews the relations among transverse-momentum dependent parton distributions (TMDs) within quark models, explaining their physical origin and how model assumptions influence these relations.

Contribution

It provides a comprehensive review of the derivation and physical basis of TMD relations in various quark models, highlighting the conditions under which they hold.

Findings

Relations among TMDs are rooted in quark-spin structure.

Model assumptions determine the validity of TMD relations.

Explicit examples illustrate the implementation of conditions in different models.

Abstract

Transverse-momentum dependent parton distributions (TMDs) are studied in the framework of quark models. In particular, quark-model relations among TMDs are reviewed, elucidating their physical origin in terms of the quark-spin structure in the nucleon. The formal aspects of the derivation of these relations are complemented with explicit examples, emphasizing how and to which extent the conditions which lead to relations among TMDs are implemented in different classes of quark models.