QCD and Light-Front Holography
The soft-wall AdS/QCD model, modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics. The model predicts a zero-mass pion for zero-mass quarks and a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number N. Light-Front Holography maps the amplitudes which are functions of the fifth dimension variable z of anti-de Sitter space to a corresponding hadron theory quantized on the light front. The resulting Lorentz-invariant relativistic light-front wave equations are functions of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. The result is to a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryon light-quark bound states, which in turn predict the behavior of the pion and nucleon form factors. The theory implements chiral symmetry in a novel way: the effects of chiral symmetry breaking increase as one goes toward large interquark separation, consistent with spectroscopic data, and the the hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. The soft-wall model also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function which agrees with the effective coupling {alpha}{sub g1} extracted from the Bjorken sum rule. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method in order to systematically include the QCD interaction terms. A new perspective on quark and gluon condensates is also reviewed.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 992880
- Report Number(s):
- SLAC-PUB-14258; arXiv:1009.4232; TRN: US1007913
- Journal Information:
- Acta Phys.Polon.B41:2605-2643,2010, Conference: Invited talk at 50th Cracow School of Theoretical Physics: Developments in particle physics from a 50 year perspective of the Cracow School, Zakopane, Poland, 9-19 Jun 2010
- Country of Publication:
- United States
- Language:
- English
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71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMPLITUDES
BARYONS
BOUND STATE
CHIRAL SYMMETRY
EIGENSTATES
FORM FACTORS
GLUONS
HADRONS
HOLOGRAPHY
MESONS
NUCLEONS
ORBITAL ANGULAR MOMENTUM
PIONS
PROTONS
QUANTUM CHROMODYNAMICS
QUANTUM NUMBERS
QUARKS
SPECTRA
SUM RULES
WAVE EQUATIONS
Phenomenology-HEP
Theory-HEP
HEPPH
HEPTH