211 research outputs found
Holographic Pomeron: Saturation and DIS
We briefly review the approach to dipole-dipole scattering in holographic QCD
developed in ARXIV:1202.0831. The Pomeron is modeled by exchanging closed
strings between the dipoles and yields Regge behavior for the elastic
amplitude. We calculate curvature corrections to this amplitude in both a
conformal and confining background, identifying the holographic direction with
the virtuality of the dipoles. The it wee-dipole density is related to the
string tachyon diffusion in both virtuality and the transverse directions. We
give an explicit derivation of the dipole saturation momentum both in the
conformal and confining metric. Our holographic result for the dipole-dipole
cross section and the it wee-dipole density in the conformal limit are shown to
be identical in form to the BFKL pomeron result when the non-critical string
transverse dimension is . The total dipole-dipole cross section is
compared to DIS data from HERA
Classical Strongly Coupled QGP II: Screening and Equation of State
We analyze the screening and bulk energy of a classical and strongly
interacting plasma of color charges, a model we recently introduced for the
description of a quark-gluon plasma at T=(1-3)Tc. The partition function is
organized around the Debye-Huckel limit. The linear Debye-Huckel limit is
corrected by a virial expansion. For the pressure, the expansion is badly
convergent even in the dilute limit. The non-linear Debye-Huckel theory is
studied numerically as an alternative for moderately strong plasmas. We use
Debye theory of solid to extend the analysis to the crystal phase at very
strong coupling. The analytical results for the bulk energy per particle
compare well with the numerical results from molecular dynamics simulation for
all couplings.Comment: 9 pages, 5 figure
The Chiral Model of Sakai-Sugimoto at Finite Baryon Density
In the context of holographic QCD we analyze Sakai-Sugimoto's chiral model at
finite baryon density and zero temperature. The baryon number density is
introduced through compact D4 wrapping S^4 at the tip of D8-\bar{D8}. Each
baryon acts as a chiral point-like source distributed uniformly over R^3, and
leads a non-vanishing U(1)_V potential on the brane. For fixed baryon charge
density n_B we analyze the bulk energy density and pressure using the canonical
formalism. The baryonic matter with point like sources is always in the
spontaneously broken phase of chiral symmetry, whatever the density. The
point-like nature of the sources and large N_c cause the matter to be repulsive
as all baryon interactions are omega mediated. Through the induced DBI action
on D8-\bar{D8}, we study the effects of the fixed baryon charge density n_B on
the pion and vector meson masses and couplings. Issues related to vector
dominance in matter in the context of holographic QCD are also discussed.Comment: V3: 39 pages, 16 figures, minor corrections, version to appear in
JHEP. V2: references added, typos correcte
Holographic Pomeron and the Schwinger Mechanism
We revisit the problem of dipole-dipole scattering via exchanges of soft
Pomerons in the context of holographic QCD. We show that a single closed string
exchange contribution to the eikonalized dipole-dipole scattering amplitude
yields a Regge behavior of the elastic amplitude; the corresponding slope and
intercept are different from previous results obtained by a variational
analysis of semi-classical surfaces. We provide a physical interpretation of
the semi-classical worldsheets driving the Regge behavior for (-t)>0 in terms
of worldsheet instantons. The latter describe the Schwinger mechanism for
string pair creation by an electric field, where the longitudinal electric
field E_L=\sigma_T tanh(\chi/2) at the origin of this non-perturbative
mechanism is induced by the relative rapidity {\chi} of the scattering dipoles.
Our analysis naturally explains the diffusion in the impact parameter space
encoded in the Pomeron exchange; in our picture, it is due to the Unruh
temperature of accelerated strings under the electric field. We also argue for
the existence of a "micro-fireball" in the middle of the transverse space due
to the soft Pomeron exchange, which may be at the origin of the thermal
character of multiparticle production in ep/pp collisions. After summing over
uncorrelated multi-Pomeron exchanges, we find that the total dipole-dipole
cross section obeys the Froissart unitarity bound.Comment: 17 pages, 4 figures, version 2: minor typos corrected, references
adde
Topology of the gauge-invariant gauge field in two-color QCD
We investigate solutions to a nonlinear integral equation which has a central
role in implementing the non-Abelian Gauss's Law and in constructing
gauge-invariant quark and gluon fields. Here we concern ourselves with
solutions to this same equation that are not operator-valued, but are functions
of spatial variables and carry spatial and SU(2) indices. We obtain an
expression for the gauge-invariant gauge field in two-color QCD, define an
index that we will refer to as the ``winding number'' that characterizes it,
and show that this winding number is invariant to a small gauge transformation
of the gauge field on which our construction of the gauge-invariant gauge field
is based. We discuss the role of this gauge field in determining the winding
number of the gauge-invariant gauge field. We also show that when the winding
number of the gauge field is an integer , the gauge-invariant
gauge field manifests winding numbers that are not integers, and are
half-integers only when .Comment: 26 pages including 6 encapsulated postscript figures. Numerical
errors have been correcte
Chiral effective action with heavy quark symmetry
We derive an effective action combining chiral and heavy quark symmetry,
using approximate bosonization techniques of QCD. We explicitly show that the
heavy-quark limit is compatible with the large (number of color) limit in
the meson sector, and derive specific couplings between the light and heavy
mesons (, , ...) and their chiral partners. The relevance of this
effective action to solitons with heavy quarks describing heavy baryons is
discussed.Comment: 14 pages, SUNY-NTG-92/2
Multibaryons in the collective coordinate approach to the SU(3) Skyrme model
We obtain the rotational spectrum of strange multibaryon states by performing
the SU(3) collective coordinate quantization of the static multi-Skyrmions.
These background configurations are given in terms of rational maps, which are
very good approximations and share the same symmetries as the exact solutions.
Thus, the allowed quantum numbers in the spectra and the structure of the
collective Hamiltonians we obtain are also valid in the exact case. We find
that the predicted spectra are in overall agreement with those corresponding to
the alternative bound state soliton model.Comment: 16 pages, 1 figur
Gluons at finite temperature in Landau gauge Yang--Mills theory
The infrared behavior of Yang-Mills theory at finite temperature provides
access to the role of confinement. In this review recent results on this topic
from lattice calculations and especially Dyson-Schwinger studies are discussed.
These indicate persistence of a residual confinement even in the
high-temperature phase. The confinement mechanism is very similar to the one in
the vacuum for the chromomagnetic sector. In the chromoelectric sector
screening occurs at the soft scale g^2T, although not leading to a perturbative
behavior.Comment: 15 pages, 4 figures, invited brief review for MPL
Semiclassical Double-Pomeron Production of Glueballs and
A semiclassical theory of high energy scattering based on interrupted
tunneling (instantons) or QCD sphaleron production has been recently developed
to describe the growing hadronic cross section and properties of the soft
Pomeron. In this work we address double-pomeron processes in this framework for
the first time. We specifically derive the cross section for central production
of parity even and odd clusters, scalar and pseudoscalar glueballs, and
in parton-parton scattering at high energy. We show that the specific
dependence of the production cross section on all its kinematical variables
compares favorably with the UA8 data on inclusive cluster production, as well
as the WA102 data on exclusive central production of scalar glueball and
, in double-pomeron exchange scattering. The magnitude of the cross
section and its dependece on kinematic variables is correct, explaining in
particular a large deviation from the Pomeron factorization at cluster masses
in the range GeV reported by UA8
Prompt Quark Production by exploding Sphalerons
Following recent works on production and subsequent explosive decay of QCD
sphaleron-like clusters, we discuss the mechanism of quark pair production in
this process. We first show how the gauge field explosive solution of Luscher
and Schechter can be achieved by non-central conformal mapping from the
O(4)-symmetric solution. Our main result is a new solution to the Dirac
equation in real time in this configuration, obtained by the same inversion of
the fermion O(4) zero mode. It explicitly shows how the quark acceleration
occurs, starting from the spherically O(3) symmetric zero energy chiral quark
state to the final spectrum of non-zero energies.
The sphaleron-like clusters with any Chern-Simons number always produce quarks, and the antisphaleron-like clusters the
chirality opposite.
The result are relevant for hadron-hadron and nucleus-nucleus collisions at
large , wherein such clusters can be produced
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