AdS/QCD and Applications of Light-Front Holography

TL;DR

This paper explores how light-front holography connects higher-dimensional AdS space with hadronic wavefunctions in physical space, providing insights into QCD confinement, hadron structure, and transition form factors.

Contribution

It offers a semiclassical AdS/QCD framework linking AdS space to hadron wavefunctions, including novel calculations of transition form factors and insights into confinement effects.

Findings

Calculated photon-to-meson transition form factors for various mesons.

Identified the AdS coordinate with a light-front variable for hadron structure.

Discussed confinement effects on quark and gluon condensates.

Abstract

Light-Front Holography leads to a rigorous connection between hadronic amplitudes in a higher dimensional anti-de Sitter (AdS) space and frame-independent light-front wavefunctions of hadrons in 3+1 physical space-time, thus providing a compelling physical interpretation of the AdS/CFT correspondence principle and AdS/QCD, a useful framework which describes the correspondence between theories in a modified AdS$_5$ background and confining field theories in physical space-time. To a first semiclassical approximation, where quantum loops and quark masses are not included, this approach leads to a single-variable light-front Schr\"odinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate $z$ in AdS space is uniquely identified with a Lorentz-invariant coordinate $\zeta$ which measures the separation of the constituents within a hadron at equal light-front time. The internal structure of hadrons is explicitly introduced and the angular momentum of the constituents plays a key role. We give an overview of the light-front holographic approach to strongly coupled QCD. In particular, we study the photon-to-meson transition form factors (TFFs) $F_{M \gamma}(Q^2)$ for $\gamma \gamma^* \to M$ using light-front holographic methods. The results for the TFFs for the $\eta$ and $\eta^\prime$ mesons are also presented. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates. A method for computing the hadronization of quark and gluon jets at the amplitude level is outlined.