60 research outputs found
Taming the BFKL Intercept via Gluon Saturation
We show that the inclusion of parton density effects in the perturbative
small-x evolution reduces the strength of the powerlike growth of total
hadronic cross sections.Comment: 4 pages, 2 figures, Proceedings for Quark Matter 200
No Froissart Bound from Gluon Saturation
In the previous work hep-ph/0112140, hep-ph/0204277, we showed that while the
nonlinear QCD evolution equation of Balitsky and Kovchegov (BK) leads to
saturation of the scattering amplitude locally in impact parameter space, it
does not unitarize the total cross section. This result was recently challenged
by Ferreiro, Iancu, Itakura and McLerran (FIIM) who claim that the
dipole-hadron cross section computed from the BK equation saturates the
Froissart bound. In this comment, we point to a fundamental error in the
argument of FIIM which invalidates their conclusion. We show that if the total
cross section violates unitarity for a coloured scattering probe, it does so
also for a colourless scattering probe.Comment: 5 pages LaTex, final version to be published in Phys. Lett. B, Note
added referring to recent controvers
CGC for Ultra-Peripheral Pb+Pb Collisions at the Large Hadron Collider: a more realistic calculation
We provide the first calculation of two-gluon production at mid-rapidity in
ultra-peripheral collisions in the Color Glass Condensate framework. To
estimate systematic uncertainty associated with poor understanding of the wave
function of the nearly real photon, we consider two diametrically different
models: the dilute quark-antiquark dipole approximation and a vector meson, in
which color charge density is approximated by McLerran-Venugopalan model. In
the experimentally relevant range, the target nucleus can be faithfully
approximated by a highly saturated state. This simplification enables us to
perform efficient numerical simulations and extract the two-gluon correlation
functions and the associated azimuthal harmonics.Comment: 35 pages,8 figure
Nonlinear QCD Evolution: Saturation without Unitarization
We consider the perturbative description of saturation based on the nonlinear
QCD evolution equation of Balitsky and Kovchegov (BK). Although the nonlinear
corrections lead to saturation of the scattering amplitude locally in impact
parameter space, we show that they do not unitarize the total cross section.
The total cross section for the scattering of a strongly interacting probe on a
hadronic target is found to grow exponentially with rapidity. The origin of
this violation of unitarity is the presence of long range Coulomb fields away
from the saturation region. The growth of these fields with rapidity is not
tempered by the nonlinearity of the BK equation.Comment: 4 pages, RevTe
The Chang-Refsdal Lens Revisited
This paper provides a complete theoretical treatment of the point-mass lens
perturbed by constant external shear, often called the Chang-Refsdal lens. We
show that simple invariants exist for the products of the (complex) positions
of the four images, as well as moment sums of their signed magnifications. The
image topographies and equations of the caustics and critical curves are also
studied. We derive the fully analytic expressions for precaustics, which are
the loci of non-critical points that map to the caustics under the lens
mapping. They constitute boundaries of the region in the image domain that maps
onto the interior of the caustics. The areas under the critical curves,
caustics and precaustics are all evaluated, which enables us to calculate the
mean magnification of the source within the caustics. Additionally, the exact
analytic expression for the magnification distribution for the source in the
triangular caustics is derived, as well as a useful approximate expression.
Finally, we find that the Chang-Refsdal lens with the convergence greater than
unity can exhibit third-order critical behaviour, if the reduced shear is
exactly equal to \sqrt{3}/2, and that the number of images for N-point masses
with non-zero constant shear cannot be greater than 5N-1.Comment: to appear in MNRAS (including 6 figures, 3 appendices; v2 - minor
update with corrected typos etc.
Statistical Mechanics of Kinks in (1+1)-Dimensions: Numerical Simulations and Double Gaussian Approximation
We investigate the thermal equilibrium properties of kinks in a classical
\F^4 field theory in dimensions. From large scale Langevin simulations
we identify the temperature below which a dilute gas description of kinks is
valid. The standard dilute gas/WKB description is shown to be remarkably
accurate below this temperature. At higher, ``intermediate'' temperatures,
where kinks still exist, this description breaks down. By introducing a double
Gaussian variational ansatz for the eigenfunctions of the statistical transfer
operator for the system, we are able to study this region analytically. In
particular, our predictions for the number of kinks and the correlation length
are in agreement with the simulations. The double Gaussian prediction for the
characteristic temperature at which the kink description ultimately breaks down
is also in accord with the simulations. We also analytically calculate the
internal energy and demonstrate that the peak in the specific heat near the
kink characteristic temperature is indeed due to kinks. In the neighborhood of
this temperature there appears to be an intricate energy sharing mechanism
operating between nonlinear phonons and kinks.Comment: 28 pages (8 Figures not included, hard-copies available), Latex,
LA-UR-93-276
Dualities in Quantum Hall System and Noncommutative Chern-Simons Theory
We discuss different dualities of QHE in the framework of the noncommutative
Chern-Simons theory. First, we consider the Morita or T-duality transformation
on the torus which maps the abelian noncommutative CS description of QHE on the
torus into the nonabelian commutative description on the dual torus. It is
argued that the Ruijsenaars integrable many-body system provides the
description of the QHE with finite amount of electrons on the torus. The new
IIB brane picture for the QHE is suggested and applied to Jain and generalized
hierarchies. This picture naturally links 2d -model and 3d CS
description of the QHE. All duality transformations are identified in the brane
setup and can be related with the mirror symmetry and S duality. We suggest a
brane interpretation of the plateu transition in IQHE in which a critical point
is naturally described by WZW model.Comment: 31 pages, 4 figure
Solitonic D-branes and brane annihilation
We point out some intriguing analogies between field theoretic solitons
(topological defects) and D-branes. Annihilating soliton-antisoliton pairs can
produce stable solitons of lower dimensionality. Solitons that localize
massless gauge fields in their world volume automatically imply the existence
of open flux tubes ending on them and closed flux tubes propagating in the
bulk. We discuss some aspects of this localization on explicit examples of
unstable wall-anti-wall systems. The annihilation of these walls can be
described in terms of tachyon condensation which renders the world-volume gauge
field non-dynamical. During this condensation the world volume gauge fields
(open string states) are resonantly excited. These can later decay into closed
strings, or get squeezed into a network flux tubes similar to a network of
cosmic strings formed at a cosmological phase transition. Although, as in the
-brane case, perturbatively one can find exact time-dependent solutions,
when the energy of the system stays localized in the plane of the original
soliton, such solutions are unstable with respect to decay into open and closed
string states. Thus, when a pair of such walls annihilates, the energy is
carried away (at least) by closed string excitations (``glueballs''), which are
the lowest energy excitations about the bulk vacuum. Suggested analogies can be
useful for the understanding of the complicated D-brane dynamics and of the
production of topological defects and reheating during brane collision in the
early universe.Comment: a typo correcte
Governing Boards and Profound Organizational Change in Hospitals
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69047/2/10.1177_107755878904600204.pd
Centrality Dependence of the High p_T Charged Hadron Suppression in Au+Au collisions at sqrt(s_NN) = 130 GeV
PHENIX has measured the centrality dependence of charged hadron p_T spectra
from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T
decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction
of the contribution from hard scattering to high p_T hadron production. For
central collisions the yield at high p_T is shown to be suppressed compared to
binary nucleon-nucleon collision scaling of p+p data. This suppression is
monotonically increasing with centrality, but most of the change occurs below
30% centrality, i.e. for collisions with less than about 140 participating
nucleons. The observed p_T and centrality dependence is consistent with the
particle production predicted by models including hard scattering and
subsequent energy loss of the scattered partons in the dense matter created in
the collisions.Comment: 7 pages text, LaTeX, 6 figures, 2 tables, 307 authors, resubmitted to
Phys. Lett. B. Revised to address referee concerns. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
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