132 research outputs found
Applications of AdS/CFT Duality to QCD
Even though quantum chromodynamics is a broken conformal theory, the AdS/CFT
correspondence has led to important insights into the properties of QCD. For
example, as shown by Polchinski and Strassler, dimensional counting rules for
the power-law falloff of hadron scattering amplitudes follow from dual
holographic models with conformal behavior at short distances and confinement
at large distances. We find that one also obtains a remarkable representation
of the entire light-quark meson and baryon spectrum, including all orbital
excitations, based on only one mass parameter. We also show how hadron
light-front wavefunctions and hadron form factors in both the space-like and
time-like regions can be predicted.Comment: Invited Talk, presented at the International Conference on QCD and
Hadronic Physics, Jun 16-20, 200
Light-Front Holographic Quantum Chromodynamics
Anti-de Sitter space in five dimensions provides an exact geometrical
representation of the conformal group. Remarkably, gravity in AdS space is
holographically dual to frame-independent light-front Hamiltonian theory,
derived from the quantization of the QCD Lagrangian at fixed light-front time
. Light-front holography also leads to a precise relation
between the bound-state amplitudes in the fifth dimension of AdS space and
the variable , where 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 for the
light-front Schr\"odinger equation for hadrons with arbitrary spin .
Remarkably, 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 limit, and linear Regge trajectories with the same slope in the radial quantum number and the
orbital angular momentum . 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.Comment: Presented by SJB at the International Conference on Nuclear Theory in
the Supercomputing Era (NTSE 2013) in honor of James Vary, May 13 - May 17,
2013, Iowa State University, Ames, Iow
A dynamical model for longitudinal wave functions in light-front holographic QCD
We construct a Schrodinger-like equation for the longitudinal wave function
of a meson in the valence qq-bar sector, based on the 't Hooft model for
large-N two-dimensional QCD, and combine this with the usual transverse
equation from light-front holographic QCD, to obtain a model for mesons with
massive quarks. The computed wave functions are compared with the wave function
ansatz of Brodsky and De Teramond and used to compute decay constants and
parton distribution functions. The basis functions used to solve the
longitudinal equation may be useful for more general calculations of meson
states in QCD.Comment: 12 pages, 2 figures, RevTeX 4.1; expanded discussion, with
calculation details moved to appendice
Light-Front Holography: A First Approximation to QCD
Starting from the Hamiltonian equation of motion in QCD, we identify an
invariant light-front coordinate which allows the separation of the
dynamics of quark and gluon binding from the kinematics of constituent spin and
internal orbital angular momentum. The result is a single variable light-front
Schrodinger equation for QCD which determines the eigenspectrum and the
light-front wavefunctions of hadrons for general spin and orbital angular
momentum. This light-front wave equation is equivalent to the equations of
motion which describe the propagation of spin- modes on anti-de Sitter (AdS)
space.Comment: 4 pages. The limits of validity of the model are further discussed.
To appear in Physical Review Letter
Hadronic Spectrum of a Holographic Dual of QCD
We compute the spectrum of light hadrons in a holographic dual of QCD defined
on which has conformal behavior at short distances and
confinement at large interquark separation. Specific hadrons are identified by
the correspondence of string modes with the dimension of the interpolating
operator of the hadron's valence Fock state. Higher orbital excitations are
matched quanta to quanta with fluctuations about the AdS background. Since only
one parameter, the QCD scale , is used, the agreement with the
pattern of physical states is remarkable. In particular, the ratio of Delta to
nucleon trajectories is determined by the ratio of zeros of Bessel functions.Comment: 4 pages, REVTeX4, 2 figures. Version published in Phys. Rev. Let
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