Light-Front Holography, AdS/QCD, and Hadronic Phenomena

TL;DR

This paper explores how light-front holography and AdS/QCD provide a semiclassical, relativistic framework for understanding hadron structure and spectra, linking higher-dimensional theories to physical observables.

Contribution

It introduces a novel mapping between AdS space and light-front wavefunctions, deriving a single-variable Schrödinger equation for hadrons with confining potential.

Findings

Derived a light-front Schrödinger equation for hadrons.

Confirmed the AdS/QCD correspondence through form factor mappings.

Discussed implications of confinement on QCD condensates.

Abstract

AdS/QCD, the correspondence between theories in a modified five-dimensional anti-de Sitter space and confining field theories in physical space-time, provides a remarkable semiclassical model for hadron physics. Light-front holography allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time, thus providing a relativistic description of hadrons at the amplitude level. We identify the AdS coordinate $z$ with an invariant light-front coordinate $\zeta$ which separates the dynamics of quark and gluon binding from the kinematics of constituent spin and internal orbital angular momentum. The result is a single-variable light-front Schr\"odinger equation with a confining potential which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The mapping of electromagnetic and gravitational form factors in AdS space to their corresponding expressions in light-front theory confirms this correspondence. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates. The distinction between static structure functions, such as the probability distributions computed from the square of the light-front wavefunctions, versus dynamical structure functions which include the effects of rescattering, is emphasized. A new method for computing the hadronization of quark and gluon jets at the amplitude level, an event amplitude generator, is outlined.