Holographic QCD Advances Understanding of Hadron Spectrum and Confinement Scale

The fundamental principles governing the strong force, described by Quantum Chromodynamics, remain a significant challenge in modern physics, and researchers continually seek new ways to understand its complex behaviour. Guy F. de Teramond, working independently, investigates the boundaries within which the holographic principle, a concept borrowed from gravity and black holes, can accurately model the interactions of quarks and gluons within hadrons. This work establishes that a holographic description of QCD is most reliable when considering high-energy particle collisions where numerous internal components contribute in a coordinated manner, offering a precise definition of the conditions under which this powerful theoretical tool remains valid. By linking the internal structure of hadrons to a holographic coordinate and enforcing mathematical consistency, this research extends the applicability of holographic QCD across a broader range of energy scales, ultimately providing a more unified and accurate picture of the strong force.

The corresponding quantity is the invariant transverse separation between quarks and gluons, ζ, which is identified with the holographic coordinate z in holographic light-front QCD. By embedding the internal structure of hadrons and implementing an effective superconformal symmetry, the mapping between quantum states and classical gravity, central to the holographic principle, yields new analytic insights into the strong-interaction dynamics responsible for the emergence of a confinement scale and the observed hadron spectrum.

Holographic Light-Front QCD and Hadron Structure

Scientists are developing holographic light-front QCD, a theoretical framework to describe the strong force, Quantum Chromodynamics (QCD), in a non-perturbative way. This approach combines holography, inspired by string theory, with light-front quantization, a technique suited for studying the internal structure of hadrons and their interactions. The goal is to understand confinement, the mechanism by which quarks are bound within hadrons, and the observed spectrum of particles. A key concept is emergent superconformal symmetry, which appears at low energies even though the underlying theory, QCD, does not possess it exactly.

This symmetry predicts a relationship between the spectra of baryons and mesons, offering a testable prediction of the model. The framework is used to calculate hadron masses and properties, including those containing heavy quarks. Research focuses on understanding the strong coupling constant at low energies, where standard calculations fail. Holographic light-front QCD aims to provide a consistent description of its evolution with energy scale and suggests a possible single-scale dependence for the Pomeron, a key component in high-energy scattering. Scientists are extending the model to high energies to provide a complete description of the coupling across all scales. The framework also calculates Generalized Parton Distributions, offering a more complete picture of nucleon structure than traditional methods. Applications include studying the distribution of gluons within protons and pions, and exploring connections between entanglement and high-energy scattering behavior.

Holographic QCD Validity Depends on Virtuality and Coherence

Scientists are defining the limits of applicability for holographic models within Quantum Chromodynamics. Their work focuses on virtuality, a measure of deviation from a particle’s mass shell, and coherence, the degree of phase alignment, as determinants for when holographic models accurately represent QCD dynamics. They measure virtuality using the invariant transverse separation between quarks and gluons. Results reveal that a gravity dual to physical QCD emerges specifically within the Regge limit of high-energy scattering, a regime characterized by the coherent participation of numerous partonic degrees of freedom.

This finding provides a quantitative definition for the domain where holographic QCD can be reliably applied and tested against experimental data. Measurements confirm that this dual description is restricted to scenarios with a high density of gluons at very small values of x, consistent with observations from high-energy experiments. The research extends the holographic framework beyond the infrared domain by enforcing analyticity and incorporating exact QCD constraints. Recent work demonstrates the extension of effective strong coupling from the Regge-limit domain, through a near-perturbative transition region, and into the ultraviolet Bjorken-limit domain, providing a unified and precise nonperturbative description of the strong coupling across all virtuality scales. Data from measurements of the proton structure function at HERA align with Regge behavior and Pomeron exchange, validating this dominance across a wide range of energies. The team defines a coherence length, inversely proportional to virtuality, demonstrating that at low virtuality, states maintain coherence over extended intervals, enabling nonperturbative dynamics to form bound states.

Holographic QCD and Hadron Dynamics Revealed

This research establishes a framework for understanding the applicability of holographic concepts to quantum chromodynamics. By utilizing light-front quantization and examining the virtuality and coherence of interactions, scientists have defined the Regge limit of high-energy scattering as the domain where a holographic duality to physical QCD emerges. This work demonstrates that the mapping between states, central to the holographic principle, provides analytical insights into the dynamics governing confinement and the observed spectrum of hadrons. The team successfully extended this holographic framework across all scales of virtuality, from the high-energy Regge limit down to the ultraviolet Bjorken limit. This achievement yields a unified and precise description of the strong coupling, offering a comprehensive nonperturbative approach to understanding the strong interaction. While acknowledging limitations in fully capturing all aspects of QCD, particularly in the infrared domain, future research will refine the effective coupling scheme and continue testing holographic predictions against experimental data.