6,449 research outputs found
Momentum Space Integral Equations for Three Charged Particles: Diagonal Kernels
It has been a long-standing question whether momentum space integral
equations of the Faddeev type are applicable to reactions of three charged
particles, in particular above the three-body threshold. For, the presence of
long-range Coulomb forces has been thought to give rise to such severe
singularities in their kernels that the latter may lack the compactness
property known to exist in the case of purely short-range interactions.
Employing the rigorously equivalent formulation in terms of an
effective-two-body theory we have proved in a preceding paper [Phys. Rev. C
{\bf 61}, 064006 (2000)] that, for all energies, the nondiagonal kernels
occurring in the integral equations which determine the transition amplitudes
for all binary collision processes, possess on and off the energy shell only
integrable singularities, provided all three particles have charges of the same
sign, i.e., all Coulomb interactions are repulsive. In the present paper we
prove that, for particles with charges of equal sign, the diagonal kernels, in
contrast, possess one, but only one, nonintegrable singularity. The latter can,
however, be isolated explicitly and dealt with in a well-defined manner. Taken
together these results imply that modified integral equations can be
formulated, with kernels that become compact after a few iterations. This
concludes the proof that standard solution methods can be used for the
calculation of all binary (i.e., (in-)elastic and rearrangement) amplitudes by
means of momentum space integral equations of the effective-two-body type.Comment: 36 pages, 2 figures, accepted for publication in Phys. Rev.
Proton-Deuteron Elastic Scattering from 2.5 to 22.5 MeV
We present the results of a calculation of differential cross sections and
polarization observables for proton-deuteron elastic scattering, for proton
laboratory energies from 2.5 to 22.5 MeV. The Paris potential parametrisation
of the nuclear force is used. As solution method for the charged-composite
particle equations the 'screening and renormalisation approach' is adopted
which allows to correctly take into account the Coulomb repulsion between the
two protons. Comparison is made with the precise experimental data of Sagara et
al. [Phys. Rev. C 50, 576 (1994)] and of Sperison et al. [Nucl. Phys. A422, 81
(1984)].Comment: 24 pages, 8 eps figures, uses REVTe
Long-range behavior of the optical potential for the elastic scattering of charged composite particles
The asymptotic behavior of the optical potential, describing elastic
scattering of a charged particle off a bound state of two charged, or
one charged and one neutral, particles at small momentum transfer
or equivalently at large intercluster distance
, is investigated within the framework of the exact three-body
theory. For the three-charged-particle Green function that occurs in the exact
expression for the optical potential, a recently derived expression, which is
appropriate for the asymptotic region under consideration, is used. We find
that for arbitrary values of the energy parameter the non-static part of the
optical potential behaves for as
. From this we derive for the
Fourier transform of its on-shell restriction for the behavior , i.e.,
dipole or quadrupole terms do not occur in the coordinate-space asymptotics.
This result corroborates the standard one, which is obtained by perturbative
methods. The general, energy-dependent expression for the dynamic
polarisability is derived; on the energy shell it reduces to the
conventional polarisability which is independent of the energy. We
emphasize that the present derivation is {\em non-perturbative}, i.e., it does
not make use of adiabatic or similar approximations, and is valid for energies
{\em below as well as above the three-body dissociation threshold}.Comment: 35 pages, no figures, revte
The Political Economy of Institutions and Corruption in American States.
Theoretically, this paper draws on political agency theory to formulate hypotheses. Empirically, it shows that political institutions have a role in explaining the prevalence of political corruption in American states. In the states, a set of democracies where the rule of law is relatively well established and the confounding effects of differing electoral systems and regimes are absent, institutional variables relating to the openness of the political system inhibit corruption. That is, other things equal, the extent to which aspiring politicians can enter and gain financial backing, and to which voters can focus their votes on policies and thereby hold incumbent politicians accountable for policy outcomes and find substitutes for them if dissatisfied with those outcomes, reduce corruption as a general problem of agency. These institutional effects are estimated in the presence of controls for variables representing other approaches.
Inequality and Corruption: Evidence from US States
High-quality data on state-level inequality and incomes, panel data on corruption convictions, and careful attention to the consequences of including or excluding fixed effects in the panel specification allow us to estimate the impact of income considerations on the decision to undertake corrupt acts. Following efficiency wage arguments, for a given institutional environment the corruptible employee’s or official’s decision to engage in corruption is affected by relative wages and expected tenure in the public sector, the probability of detection, the cost of fines and jail terms, and the degree of inequality, which indicate diminished prospects facing those convicted of corruption. In US states over 25 years we show that inequality and higher government relative wages significantly and robustly produce less corruption. This reverses other findings of a positive association between inequality and corruption, which we show arises from long-run joint causation by unobserved factors.corruption; rent seeking; inequality; Gini coefficient; efficiency wage; public sector wages
Enforcement and Public Corruption: Evidence from US States
We use high-quality panel data on corruption convictions, new panels of assistant U.S. attorneys and relative public sector wages, and careful attention to the consequences of modeling endogeneity to estimate the impact of prosecutorial resources on criminal convictions of those who undertake corrupt acts. Consistent with “system capacity” arguments, we find that greater prosecutor resources result in more convictions for corruption, other things equal. We find more limited, recent evidence for the deterrent effect of increased prosecutions. We control for and confirm in a panel context the effects of many previously identified correlates and causes of corruption. By explicitly determining the allocation of prosecutorial resources endogenously from past corruption convictions and political considerations, we show that this specification leads to larger estimates of the effect of resources on convictions. The results are robust to various ways of measuring the number of convictions as well as to various estimators.corruption; rent seeking; enforcement; efficiency wage; public sector wages; system capacity
The Political Budget Cycle is Where You Can't See It: Transparency and Fiscal Manipulation
We investigate the effects of fiscal transparency and political polarization on the prevalence of electoral cycles in fiscal balance. The recent political economy literature on electoral cycles identifies such cycles mainly in weak and recent democracies. In contrast, we show, conditioning on a new index of institutional fiscal transparency, that electoral cycles in fiscal balance are a feature also of advanced industrialized economies. Using a sample of nineteen OECD countries in the 1990’s, we identify a persistent pattern of electoral cycles in low(er) transparency countries, while no such cycles can be observed in high(er) transparency countries. Furthermore, we find, in accordance with recent theory, that electoral cycles are larger in more politically polarized countries.fiscal transparency; political polarization; fiscal policy; budget deficits; political budget cycles; electoral policy cycles
Political and Judicial Checks on Corruption: Evidence from American State Governments
The paper investigates the effects of checks and balances on corruption. Within a presidential system, effective separation of powers is achieved under divided government, with the executive and legislative branches being controlled by different political parties. When government is unified, no effective separation exists even within a presidential system, but, we argue, can be partially restored by having an accountable judiciary. Our empirical findings show that divided government and elected, rather than appointed, state supreme court judges are associated with lower corruption and, furthermore, that the effect of an accountable judiciary is stronger under unified government, where government cannot control itself. The effect of an accountable judiciary seems to be driven primarily by judges chosen through direct elections, rather than those exposed to a retention vote following appointment.separation of powers; corruption; rent seeking; checks and balances; political institutions; judicial independence; rule of law
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