206 research outputs found
Mapping String States into Partons: Form Factors and the Hadron Spectrum in AdS/QCD
New developments in holographic QCD are described in this talk in the context
of the correspondence between string states in AdS and light-front
wavefunctions of hadronic states in physical space-time.Comment: 7 pages, 3 figures. Presented at Seventh Workshop on Continuous
Advances in QCD, Minneapolis, May 11-14, 200
Light-Front Holography and QCD Hadronization at the Amplitude Level
Light-front holography allows hadronic amplitudes in the AdS/QCD fifth
dimension to be mapped to frame-independent light-front wavefunctions of
hadrons in physical space-time, thus providing a relativistic description of
hadrons at the amplitude level. The AdS coordinate z is identified with an
invariant light-front coordinate zeta which separates 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. A new
method for computing the hadronization of quark and gluon jets at the amplitude
level using AdS/QCD light-front wavefunctions is outlined.Comment: Talk presented by SJB at the International Conference on Particles
and Nuclei (PANIC08), Eilat, Israel, November 9-14, 200
Light-Front Holography and the Light-Front Schrodinger Equation
One of the most important nonperturbative methods for solving QCD is
quantization at fixed light-front time, \tau = t+z/c -- Dirac's "Front Form".
The eigenvalues of the light-front QCD Hamiltonian predict the hadron spectrum
and the eigensolutions provide the light-front wavefunctions which describe
hadron structure. More generally, we show that the valence Fock-state
wavefunctions of the light-front QCD Hamiltonian satisfy a single-variable
relativistic equation of motion, analogous to the nonrelativistic radial
Schr\"odinger equation, with an effective confining potential U which
systematically incorporates the effects of higher quark and gluon Fock states.
We outline a method for computing the required potential from first principles
in QCD. The holographic mapping of gravity in AdS space to QCD, quantized at
fixed light-front time, yields the same light front Schr\"odinger equation; in
fact, the soft-wall AdS/QCD approach provides a model for the light-front
potential which is color-confining and reproduces well the light-hadron
spectrum. One also derives via light-front holography a precise relation
between the bound-state amplitudes in the fifth dimension of AdS space and the
boost-invariant light-front wavefunctions describing the internal structure of
hadrons in physical space-time. The elastic and transition form factors of the
pion and the nucleons are found to be well described in this framework. The
light-front AdS/QCD holographic approach thus gives a frame-independent first
approximation of the color-confining dynamics, spectroscopy, and excitation
spectra of relativistic light-quark bound states in QCD.Comment: Invited talk, presented by SJB at the QCD Evolution Workshop, May 14
- 17, 2012, Thomas Jefferson National Accelerator Facility, Newport News,
Virgini
AdS/CFT and Exclusive Processes in QCD
The AdS/CFT correspondence between string theory in AdS space and conformal
field theories in physical space-time leads to an analytic, semi-classical
model for strongly-coupled QCD which has scale invariance and dimensional
counting at short distances and color confinement at large distances. One can
use holography to map the amplitude describing the hadronic state in the fifth
dimension of Anti-de Sitter space to the light-front wavefunctions of hadrons
in physical space-time, thus providing a relativistic description of hadrons in
QCD at the amplitude level. In particular, we show that there is an exact
correspondence between the fifth-dimensional coordinate of AdS space z and a
specific impact variable zeta which measures the separation of the quark and
gluonic constituents within the hadron in ordinary space-time. New relativistic
light-front equations in ordinary space-time can then be derived which
reproduce the results obtained using the 5-dimensional theory. The effective
light-front equations possess elegant algebraic structures and integrability
properties. This connection between the AdS and the light-front representations
allows one to compute the analytic form of the frame-independent light-front
wavefunctions, the fundamental entities which encode hadron properties and
allow the computation of decay constants, form factors, deeply virtual Compton
scattering, exclusive heavy hadron decays and other exclusive scattering
amplitudes. As specific examples we compute the pion coupling constant and
study the behavior of the pion form factor in the space and time-like regions.
We also determine the Dirac form factors of the proton and neutron in the
space-like region.Comment: 29 pages, 7 figures. Invited talk, presented at the Workshop on
Exclusive Reactions at High Momentum Transfer 21-24 May 2007, Newport News,
Virgini
Light-Front Holography and Novel Effects in QCD
The correspondence between theories in anti-de Sitter space and conformal
field theories in physical space-time leads to an analytic, semiclassical model
for strongly-coupled QCD. Light-front holography allows hadronic amplitudes in
the AdS fifth dimension to be mapped to frame-independent light-front
wavefunctions of hadrons in physical space-time, thus providing a relativistic
description of hadrons at the amplitude level. We identify the AdS coordinate
with an invariant light-front coordinate which separates 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
Schr\"odinger equation for QCD which determines the eigenspectrum and the
light-front wavefunctions of hadrons for general spin and orbital angular
momentum. The mapping of electromagnetic and gravitational form factors in AdS
space to their corresponding expressions in light-front theory confirms this
correspondence. Some novel features of QCD are discussed, including the
consequences of confinement for quark and gluon condensates and the behavior of
the QCD coupling in the infrared. The distinction between static structure
functions such as the probability distributions computed from the square of the
light-front wavefunctions versus dynamical structure functions which include
the effects of rescattering is emphasized. A new method for computing the
hadronization of quark and gluon jets at the amplitude level, an event
amplitude generator, is outlined.Comment: 16 pages, 3 figures. Presented by SJB at the XIII Mexican School of
Particles and Field
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