Light-Front Holography and the Light-Front Schrodinger Equation

TL;DR

This paper develops a light-front holographic approach to QCD, deriving a Schrödinger-like equation for hadron structure, and demonstrates its effectiveness in predicting hadron spectra and form factors.

Contribution

It introduces a novel light-front Schrödinger equation derived from holographic QCD, linking AdS space to hadron structure and spectra.

Findings

Reproduces light-hadron spectrum accurately

Describes pion and nucleon form factors well

Provides a first approximation of confinement dynamics

Abstract

One of the most important nonperturbative methods for solving QCD is quantization at fixed light-front time, \tau = t+z/c -- Dirac's "Front Form". The eigenvalues of the light-front QCD Hamiltonian predict the hadron spectrum and the eigensolutions provide the light-front wavefunctions which describe hadron structure. More generally, we show that the valence Fock-state wavefunctions of the light-front QCD Hamiltonian satisfy a single-variable relativistic equation of motion, analogous to the nonrelativistic radial Schr\"odinger equation, with an effective confining potential U which systematically incorporates the effects of higher quark and gluon Fock states. We outline a method for computing the required potential from first principles in QCD. The holographic mapping of gravity in AdS space to QCD, quantized at fixed light-front time, yields the same light front Schr\"odinger equation; in fact, the soft-wall AdS/QCD approach provides a model for the light-front potential which is color-confining and reproduces well the light-hadron spectrum. One also derives via light-front holography a precise relation between the bound-state amplitudes in the fifth dimension of AdS space and the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. The elastic and transition form factors of the pion and the nucleons are found to be well described in this framework. The light-front AdS/QCD holographic approach thus gives a frame-independent first approximation of the color-confining dynamics, spectroscopy, and excitation spectra of relativistic light-quark bound states in QCD.