The Hadron-Parton Bridge, From the QCD Vacuum to Partons

TL;DR

This paper develops a unified framework connecting the nonperturbative rest-frame description of hadrons with the high-energy parton picture using the Instanton Liquid Model, enabling realistic calculations of hadronic structure functions and form factors.

Contribution

It introduces a novel approach that combines instanton-induced dynamics with light-front Hamiltonians to connect hadronic spectroscopy with partonic distributions in QCD.

Findings

Consistent descriptions of hadron spectra and partonic structures.

Realistic calculations of PDFs, GPDs, and form factors at low scales.

Natural emergence of hadron mechanical properties from the model.

Abstract

Quantum Chromodynamics (QCD) exhibits complementary descriptions of hadrons: a rest-frame picture based on confinement, chiral symmetry breaking and interquark forces, and a high-energy light-front picture expressed through parton distributions (PDFs,TMDs,GPDs) and form factors. This review develops a unified framework that connects these two domains. It is based mostly on multiple studies by the authors in the past few years. Using the Instanton Liquid Model (ILM) to capture essential nonperturbative features of the QCD vacuum, we derive effective interactions for mesons, baryons, and multiquark states, construct their wave functions in hyperspherical coordinates, and boost them to the light front. The resulting light-front Hamiltonians, incorporating both perturbative and instanton-induced dynamics in the Wilsonian spirit, provide realistic nonperturbative inputs for computing PDFs, DAs, GPDs, quasi-distributions, and gravitational form factors at a well-defined low scale. The connection to perturbative QCD is then established by matching gradient-flow-renormalized operators and LF wave functions to the standard $\overline{\rm MS}$ scheme. Perturbative DGLAP and ERBL evolution then connects these predictions to experimentally accessible regimes. % This approach is applied to quarkonia, glueballs, light mesons, baryons, tetraquarks, pentaquarks, and higher multiquark hadrons, yielding consistent descriptions of both their spectra and partonic structure. Special emphasis is placed on the energy-momentum tensor and the mechanical properties of hadrons, which emerge naturally from the same dynamical ingredients. Overall, the framework demonstrates a clear continuity between hadronic spectroscopy and partonic observables, offering a coherent multiscale picture of hadron structure rooted in the underlying dynamics of QCD.