1,460 research outputs found
Hadron-nucleus scattering in the local reggeon model with pomeron loops for realistic nuclei
Contribution of simplest loops for hadron-nucleus scattering cross-sections
is studied in the Local Reggeon Field Theory with a supercritical pomeron. It
is shown that inside the nucleus the supercritical pomeron transforms into a
subcritical one, so that perturbative treatment becomes possible. The pomeron
intercept becomes complex, which leads to oscillations in the cross-sections.Comment: 13 pages, 6 figure
BFKL pomeron propagator in the external field of the nucleus
It is shown by numerical calculations that the convoluted QCD pomeron
propagator in the external field created by a solution of the
Balitsky-Kovchegov equation in the nuclear matter vanishes at high rapidities.
This may open a possibility to apply the perturbative approach for the
calculation of pomeron loops.Comment: 17 pages, 15 figure
Patchiness and Demographic Noise in Three Ecological Examples
Understanding the causes and effects of spatial aggregation is one of the
most fundamental problems in ecology. Aggregation is an emergent phenomenon
arising from the interactions between the individuals of the population, able
to sense only -at most- local densities of their cohorts. Thus, taking into
account the individual-level interactions and fluctuations is essential to
reach a correct description of the population. Classic deterministic equations
are suitable to describe some aspects of the population, but leave out features
related to the stochasticity inherent to the discreteness of the individuals.
Stochastic equations for the population do account for these
fluctuation-generated effects by means of demographic noise terms but, owing to
their complexity, they can be difficult (or, at times, impossible) to deal
with. Even when they can be written in a simple form, they are still difficult
to numerically integrate due to the presence of the "square-root" intrinsic
noise. In this paper, we discuss a simple way to add the effect of demographic
stochasticity to three classic, deterministic ecological examples where
aggregation plays an important role. We study the resulting equations using a
recently-introduced integration scheme especially devised to integrate
numerically stochastic equations with demographic noise. Aimed at scrutinizing
the ability of these stochastic examples to show aggregation, we find that the
three systems not only show patchy configurations, but also undergo a phase
transition belonging to the directed percolation universality class.Comment: 20 pages, 5 figures. To appear in J. Stat. Phy
Pomeron loops in the perturbative QCD with Large N_c
The lowest order pomeron loop is calculated for the leading conformal weight
with full dependence of the triple pomeron vertex on intermediate conformal
weights. The loop is found to be convergent. Its contribution to the pomeron
Green function begins to dominate already at rapidities 1015. The pomeron
pole renormalization is found to be quite small due to a rapid fall of the
triple pomeron vertex with rising conformal weights.Comment: 17 pages, 2 figure
Two parton shower background for associate W Higgs production
The estimates of the background for the associate W Higgs production, which
stems from the two parton shower production. It is about 1 - 2.5 times larger
than the signal. However, this background does not depend on the rapidity
difference between the W and the pair, while the signal peaks when
the rapidity difference is zero. The detailed calculations for the enhanced
diagrams' contribution to this process, are presented, and it is shown that the
overlapping singularities, being important theoretically, lead to a negligible
contribution for the LHC range of energiesComment: 35 pages and 10 figures in eps file
A QCD motivated model for soft interactions at high energies
In this paper we develop an approach to soft scattering processes at high
energies,which is based on two mechanisms: Good-Walker mechanism for low mass
diffractionand multi-Pomeron interactions for high mass diffraction. The
pricipal idea, that allows us to specify the theory for Pomeron interactions,
is that the so called soft processes occur at rather short distances
(r^2 \propto 1 /^2 \propto \alpha'_\pom \approx 0.01 GeV^{-2}), where
perturbative QCD is valid. The value of the Pomeron slope \alpha'_\pom was
obtained from the fit to experimental data. Using this theoretical approach we
suggest a model that fits all soft data in the ISR-Tevatron energy range, the
total, elastic, single and double diffractive cross sections, including
dependence of the differential elastic cross section, and the mass dependence
of single diffraction. In this model we calculate the survival probability of
diffractive Higgs production, and obtained a value for this observable, which
is smaller than 1% at the LHC energy range.Comment: 33pp,20 figures in eps file
Boundary conditions in the QCD nucleus-nucleus scattering problem
In the framework of the effective field theory for interacting BFKL pomerons,
applied to nucleus-nucleus scattering, boundary conditions for the classical
field equations are discussed. Correspondence with the QCD diagrams at the
boundary rapidities requires pomeron interaction with the participating nuclei
to be exponential and non-local. Commonly used 'eikonal' boundary conditions,
local and linear in fields, follow in the limit of small QCD pomeron-nucleon
coupling. Numerical solution of the classical field equations, which sum all
tree diagrams for central gold-gold scattering, demonstrates that corrected
boundary conditions lead to substantially different results, as compared to the
eikonal conditions studied in earlier publications. A breakdown of
projectile-target symmetry for particular solutions discovered earlier in
\cite{bom} is found to occur at roughly twice lower rapidity. Most important,
due to a high non-linearity of the problem, the found asymmetric solutions are
not unique but form a family growing in number with rapidity. The minimal value
for the action turns out to be much lower than with the eikonal boundary
conditions and saturates at rapidities around 10.Comment: 19 pages, 8 figure
Monopoles and Modifications of Bundles over Elliptic Curves
Modifications of bundles over complex curves is an operation that allows one to construct a new bundle from a given one. Modifications can change a topological type of bundle. We describe the topological type in terms of the characteristic classes of the bundle. Being applied to the Higgs bundles modifications establish an equivalence between different classical integrable systems. Following Kapustin and Witten we define the modifications in terms of monopole solutions of the Bogomolny equation. We find the Dirac monopole solution in the case R × (elliptic curve). This solution is a three-dimensional generalization of the Kronecker series. We give two representations for this solution and derive a functional equation for it generalizing the Kronecker results. We use it to define Abelian modifications for bundles of arbitrary rank. We also describe non-Abelian modifications in terms of theta-functions with characteristic
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
- …