2013/09/19 by Brodsky, Stanley J., de Téramond, Guy F., Dosch, Hans Günter
#FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #High Energy Physics - Theory (hep-th)
paper · doi:10.48550/arxiv.1309.4856
Anti-de Sitter space in five dimensions provides an exact geometrical representation of the conformal group. Remarkably, gravity in AdS5 space is holographically dual to frame-independent light-front Hamiltonian theory, derived from the quantization of the QCD Lagrangian at fixed light-front time τ= x0+x3. Light-front holography also leads to a precise relation between the bound-state amplitudes in the fifth dimension z of AdS space and the variable ζ, where ζ2 = b2_⊥ x(1-x) is the argument of the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. The holographic mapping of AdS space with a specific "soft-wall" dilaton yields a confining potential U(ζ2) for the light-front Schrödinger equation for hadrons with arbitrary spin J. Remarkably, U(ζ2) has a unique form of a harmonic oscillator potential if one requires that the chiral QCD action remains conformally invariant. One thus obtains an effective light-front effective theory for general spin which respects the conformal symmetry of the four-dimensional classical QCD Lagrangian. The predictions of the LF equations of motion include a zero-mass pion in the chiral mq→ 0 limit, and linear Regge trajectories M2(n,L) ∝ n+L with the same slope in the radial quantum number n and the orbital angular momentum L. The light-front AdS/QCD holographic approach gives a frame-independent representation of color-confining dynamics, Regge spectroscopy, as well as the excitation spectra of relativistic light-quark meson and baryon bound states in QCD in terms of a single mass parameter. We also briefly discuss the implications of the underlying conformal template of QCD for renormalization scale-setting, and the implications of light-front quantization for the value of the cosmological constant.