619 research outputs found
Kinematical and Dynamical Aspects of Higher-Spin Bound-State Equations in Holographic QCD
In this paper we derive holographic wave equations for hadrons with arbitrary
spin starting from an effective action in a higher-dimensional space asymptotic
to anti-de Sitter (AdS) space. Our procedure takes advantage of the local
tangent frame, and it applies to all spins, including half-integer spins. An
essential element is the mapping of the higher-dimensional equations of motion
to the light-front Hamiltonian, thus allowing a clear distinction between the
kinematical and dynamical aspects of the holographic approach to hadron
physics. Accordingly, the non-trivial geometry of pure AdS space encodes the
kinematics, and the additional deformations of AdS space encode the dynamics,
including confinement. It thus becomes possible to identify the features of
holographic QCD which are independent of the specific mechanisms of conformal
symmetry breaking. In particular, we account for some aspects of the striking
similarities and differences observed in the systematics of the meson and
baryon spectra.Comment: 43 page
Hadron Spectroscopy and Dynamics from Light-Front Holography and Conformal Symmetry
To a first semiclassical approximation one can reduce the multi-parton
light-front problem in QCD to an effective one-dimensional quantum field
theory, which encodes the fundamental conformal symmetry of the classical QCD
Lagrangian. This procedure leads to a relativistic light-front wave equation
for arbitrary spin which incorporates essential spectroscopic and
non-perturbative dynamical features of hadron physics. The mass scale for
confinement and higher dimensional holographic mapping to AdS space are also
emergent properties of this framework.Comment: 11 pages, 6 figures. Invited plenary talk, presented by GdT at the
13th International Conference on Meson-Nucleon Physics and the Structure of
the Nucleon (MENU 2013), Rome, September 30 - October 4, 201
Threefold Complementary Approach to Holographic QCD
A complementary approach, derived from (a) higher dimensional anti--de Sitter
(AdS) space, (b) light-front quantization and (c) the invariance properties of
the full conformal group in one dimension leads to a nonperturbative
relativistic light-front wave equation which incorporates essential
spectroscopic and dynamical features of hadron physics. The fundamental
conformal symmetry of the classical QCD Lagrangian in the limit of massless
quarks is encoded in the resulting effective theory. The mass scale for
confinement emerges from the isomorphism between the conformal group and
SO(2,1). This scale appears in the light-front Hamiltonian by mapping to the
evolution operator in the formalism of de Alfaro, Fubini and Furlan, which
retains the conformal invariance of the action. Remarkably, the specific form
of the confinement interaction and the corresponding modification of AdS space
are uniquely determined in this procedure.Comment: Reference added. Article accepted for publication in PL
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
Pitch-angle scattering in magnetostatic turbulence. I. Test-particle simulations and the validity of analytical results
Context. Spacecraft observations have motivated the need for a refined
description of the phase-space distribution function. Of particular importance
is the pitch-angle diffusion coefficient that occurs in the Fokker-Planck
transport equation. Aims. Simulations and analytical test-particle theories are
compared to verify the diffusion description of particle transport, which does
not allow for non-Markovian behavior. Methods. A Monte-Carlo simulation code
was used to trace the trajectories of test particles moving in turbulent
magnetic fields. From the ensemble average, the pitch-angle Fokker-Planck
coefficient is obtained via the mean square displacement. Results. It is shown
that, while excellent agreement with analytical theories can be obtained for
slab turbulence, considerable deviations are found for isotropic turbulence. In
addition, all Fokker-Planck coefficients tend to zero for high time values.Comment: 8 pages, 10 figures, accepted for publication in Astron. Astrophy
SU(2) Gluodynamics and HP1 sigma-model embedding: Scaling, Topology and Confinement
We investigate recently proposed HP1 sigma-model embedding method aimed to
study the topology of SU(2) gauge fields. The HP1 based topological charge is
shown to be fairly compatible with various known definitions. We study the
corresponding topological susceptibility and estimate its value in the
continuum limit. The geometrical clarity of HP1 approach allows to investigate
non-perturbative aspects of SU(2) gauge theory on qualitatively new level. In
particular, we obtain numerically precise estimation of gluon condensate and
its leading quadratic correction. Furthermore, we present clear evidences that
the string tension is to be associated with global (percolating) regions of
sign-coherent topological charge. As a byproduct of our analysis we estimate
the continuum value of quenched chiral condensate and the dimensionality of
regions, which localize the lowest eigenmodes of overlap Dirac operator.Comment: 22 pages, 18 ps figures, revtex4. Replaced to match published version
(PRD, to appear
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