13,648 research outputs found
Consequences of the Factorization Hypothesis in pbar p, pp, gamma p and gamma gamma Collisions
Using an eikonal analysis, we examine the validity of the factorization
theorem for nucleon-nucleon, gamma p and gamma gamma collisions. As an example,
using the additive quark model and meson vector dominance, we directly show
that for all energies and values of the eikonal, that the factorization theorem
sigma_{nn}/sigma_{gamma p} = sigma_{gamma p}/sigma_{gamma gamma} holds. We can
also compute the survival probability of large rapidity gaps in high energy
pbar p and pp collisions. We show that the survival probabilities are identical
(at the same energy) for gamma p and gamma gamma collisions, as well as for
nucleon-nucleon collisions. We further show that neither the factorization
theorem nor the reaction-independence of the survival probabilities depends on
the assumption of an additive quark model, but, more generally, depends on the
opacity of the eikonal being independent of whether the reaction is n-n, gamma
p or gamma gamma.Comment: 8 pages, Revtex, no figures. Expanded discussion, minor correction
Protective coatings for chromium alloys Final summary report, Nov. 1, 1965 - Jul. 13, 1967
Aluminum protective coatings for chromium alloy
The High Energy Behavior of the Forward Scattering Parameters---An Amplitude Analysis Update
Utilizing the most recent experimental data, we reanalyze high energy \pbar p
and pp data, using the asymptotic amplitude analysis, under the assumption that
we have reached `asymptopia'. This analysis gives strong evidence for a dependence at {\em current} energies and {\em not} ,
and also demonstrates that odderons are {\em not} necessary to explain the
experimental data.Comment: 7 pages in LaTeX, 4 figures and 5 files, uuencoded in file
"sigall.uu
Democratization’s Risk Premium: Partisan and Opportunistic Political Business Cycle Effects on Sovereign Ratings in Developing Countries
We use partisan and opportunistic political business cycle (“PBC”) considerations to develop a framework for explaining election-period decisions by credit rating agencies (“agencies”) publishing developing country sovereign risk-ratings (“ratings”). We test six hypotheses derived from the framework with 482 agency ratings for 19 countries holding 39 presidential elections from 1987-2000. We find that ratings are linked to the partisan orientation of incumbents facing election and to expectations of incumbent victory. Consistent with the framework, rating effects are sometimes greater for right-wing compared to left-wing incumbents, perhaps, because partisan PBC considerations with right-wing (left-wing) incumbents reinforce (counteract) opportunistic PBC considerations.http://deepblue.lib.umich.edu/bitstream/2027.42/39931/3/wp546.pd
DEMOCRACY’S SPREAD: Elections and Sovereign Debt in Developing Countries
We use partisan and opportunistic political business cycle (“PBC”) considerations to develop and test a framework for explaining election-period changes in credit spreads for developing country sovereign bonds. Pre-election bond spread trends are significantly linked both to the partisan orientation of incumbents facing election and to expectations of incumbent victory. Bond spreads for right-wing (leftwing) incumbents increase (decrease) as the likelihood of left-wing (right-wing) challenger victory increases. For right-wing incumbent partisan and opportunistic PBC effects bondholder risk perceptions are mutually reinforcing. For left-wing incumbents partisan PBC effects dominate bondholder risk perceptions compared to opportunistic PBC effects.http://deepblue.lib.umich.edu/bitstream/2027.42/39961/3/wp575.pd
Analytic models and forward scattering from accelerator to cosmic-ray energies
Analytic models for hadron-hadron scattering are characterized by analytical
parametrizations for the forward amplitudes and the use of dispersion relation
techniques to study the total cross section and the
parameter. In this paper we investigate four aspects related to the application
of the model to and scattering, from accelerator to cosmic-ray
energies: 1) the effect of different estimations for from
cosmic-ray experiments; 2) the differences between individual and global
(simultaneous) fits to and ; 3) the role of the
subtraction constant in the dispersion relations; 4) the effect of distinct
asymptotic inputs from different analytic models. This is done by using as a
framework the single Pomeron and the maximal Odderon parametrizations for the
total cross section. Our main conclusions are the following: 1) Despite the
small influence from different cosmic-ray estimations, the results allow us to
extract an upper bound for the soft pomeron intercept: ;
2) although global fits present good statistical results, in general, this
procedure constrains the rise of ; 3) the subtraction constant as
a free parameter affects the fit results at both low and high energies; 4)
independently of the cosmic-ray information used and the subtraction constant,
global fits with the odderon parametrization predict that, above GeV, becomes greater than , and
this result is in complete agreement with all the data presently available. In
particular, we infer at GeV and
at 500 GeV (BNL RHIC energies).Comment: 16 pages, 7 figures, aps-revtex, wording changes, corrected typos, to
appear in Physical Review
A new numerical method for obtaining gluon distribution functions , from the proton structure function
An exact expression for the leading-order (LO) gluon distribution function
from the DGLAP evolution equation for the proton structure
function for deep inelastic scattering has
recently been obtained [M. M. Block, L. Durand and D. W. McKay, Phys. Rev.
D{\bf 79}, 014031, (2009)] for massless quarks, using Laplace transformation
techniques. Here, we develop a fast and accurate numerical inverse Laplace
transformation algorithm, required to invert the Laplace transforms needed to
evaluate , and compare it to the exact solution. We obtain accuracies
of less than 1 part in 1000 over the entire and spectrum. Since no
analytic Laplace inversion is possible for next-to-leading order (NLO) and
higher orders, this numerical algorithm will enable one to obtain accurate NLO
(and NNLO) gluon distributions, using only experimental measurements of
.Comment: 9 pages, 2 figure
Ground state of a confined Yukawa plasma
The ground state of an externally confined one-component Yukawa plasma is
derived analytically. In particular, the radial density profile is computed.
The results agree very well with computer simulations on three-dimensional
spherical Coulomb crystals. We conclude in presenting an exact equation for the
density distribution for a confinement potential of arbitrary geometry.Comment: 5 pages, 4 figure
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