AdS/QCD and Applications of Light-Front Holography

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 Schrödinger 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 $\gamma {\gamma }^{\ast }\to M$ 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.

Comments: Lectures presented by SJB and GdT at the Workshop AdS/CFT and Novel Approaches to Hadron and Heavy Ion Physics, Kavli Institute of Theoretical Physics (KITPC), Beijing, China, October 19 and 20, 2010. Review Article to be published in Communications in Theoretical Physics. 61 pages, 13 figures