14,581 research outputs found
Light-Front Holography and AdS/QCD Correspondence
Light-Front Holography is a remarkable consequence of the correspondence
between string theory in AdS space and conformal field theories in
physical-space time. It allows string modes in the AdS fifth
dimension to be precisely mapped to the light-front wavefunctions of hadrons in
terms of a specific light-front impact variable which measures the
separation of the quark and gluonic constituents within the hadron. This
mapping was originally obtained by matching the exact expression for
electromagnetic current matrix elements in AdS space with the corresponding
exact expression for the current matrix element using light-front theory in
physical space-time. More recently we have shown that one obtains the identical
holographic mapping using matrix elements of the energy-momentum tensor, thus
providing an important consistency test and verification of holographic mapping
from AdS to physical observables defined on the light-front. The resulting
light-front Schrodinger equations predicted from AdS/QCD give a good
representation of the observed meson and baryon spectra and give excellent
phenomenological predictions for amplitudes such as electromagnetic form
factors and decay constants.Comment: 14 pages. Presented at QCD Down Under II, Auckland, New Zealand,
January 17-19, 200
Applications of AdS/QCD and Light-Front Holography to Baryon Physics
The correspondence between theories in anti-de Sitter space and field
theories in physical space-time leads to an analytic, semiclassical model for
strongly-coupled QCD which has scale invariance at short distances and color
confinement at large distances. These equations, for both mesons and baryons,
give a very good representation of the observed hadronic spectrum, including a
zero mass pion. 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. The meson and baryon wavefunctions derived from
light-front holography and AdS/QCD also have remarkable phenomenological
features, including predictions for the electromagnetic form factors and decay
constants. The approach can be systematically improved using light-front
Hamiltonian methods. Some novel features of QCD for baryon physics are also
discussed.Comment: Presented by SJB at the International Conference on the Structure of
Baryons, BARYONS'10, December 7-11, 2010, Osaka, Japa
Nearly Conformal QCD and AdS/CFT
The AdS/CFT correspondence is a powerful tool to study the properties of
conformal QCD at strong coupling in terms of a higher dimensional dual gravity
theory. The power-law falloff of scattering amplitudes in the non-perturbative
regime and calculable hadron spectra follow from holographic models dual to QCD
with conformal behavior at short distances and confinement at large distances.
String modes and fluctuations about the AdS background are identified with QCD
degrees of freedom and orbital excitations at the AdS boundary limit. A
description of form factors in space and time-like regions and the behavior of
light-front wave functions can also be understood in terms of a dual gravity
description in the interior of AdS.Comment: 8 pages, LateX, 3 figures. Presented at First Workshop on
Quark-Hadron Duality and the Transition to pQCD, Frascati, Italy, 6-8 June
2005. AdS LFWF mapping reexamine
Gauge/Gravity Duality and Hadron Physics at the Light-Front
We discuss some remarkable features of the light-front holographic mapping of
classical gravity in anti-de Sitter space modified by a confining dilaton
background. In particular, we show that a positive-sign dilaton solution
has better chances to describe the correct hadronic
phenomenology than the negative solution extensively
studied in the literature. We also show that the use of twist-scaling
dimensions, instead of canonical dimensions, is required to give a good
description of the spectrum and form factors of hadrons. Another key element is
the explicit connection of AdS modes of total angular momentum with the
internal structure of hadrons and the proper identification of the orbital
angular momentum of the constituents.Comment: Invited talk presented by GdT at XI Hadron Physics, Maresias Beach,
Sao Paulo, Brazil, 21-26 March 201
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
Excited Baryons in Holographic QCD
The light-front holographic QCD approach is used to describe baryon
spectroscopy and the systematics of nucleon transition form factors.Comment: Invited talk presented by GdT at NSTAR 2011, the 8th International
Workshop on the Physics of Excited Nucleons, Jefferson Laboratory, May 17 -
20, 201
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