3,561 research outputs found
New light on electromagnetic corrections to the scattering parameters obtained from experiments on pionium
We calculate the electromagnetic corrections needed to obtain isospin
invariant hadronic pion-pion s-wave scattering lengths a^0, a^2 from the
elements a_cc, a_0c of the s-wave scattering matrix for the (\pi^+ \pi^-, \pi^0
\pi^0) system at the \pi^+ \pi^- threshold. These elements can be extracted
from experiments on pionium. Our calculation uses energy independent hadronic
pion-pion potentials that satisfactorily reproduce the low-energy phase shifts
given by two-loop chiral pertur- bation theory. We also take into account an
important relativistic effect whose inclusion influences the corrections
considerably.Comment: 14 pages including 3 figures. Uses elsart.cls. Some numbers have been
updated and a few typos have been correcte
The extraction of hadronic parameters from experiments on pionium
Experimental values of the lifetime of the 1s level of pionium and of the
difference between the energies of the 2s and 2p levels yield values of the
a(0c) and a(cc) elements of the s-wave scattering matrix for the 2-channel (pi+
pi-, pi0 pi0) system at the pi+ pi- threshold. We develop a method for
obtaining the isospin invariant quanties a20 - a00 and 2a00 + a20 from a(0c)
and a(cc). We emphasize that the isospin invariant scattering lengths a00 and
a20 universally used in the literature cannot be considered to be purely
hadronic quantities.Comment: 17 pages, Revtex, 1 postscript figure, new version of figure which
removes ghostscript problem
Analysis of the low-energy charge-exchange data
We analyse the charge-exchange (CX) measurements
below pion laboratory kinetic energy of 100 MeV. After the removal of five
degrees of freedom from the initial database, we combine it with the truncated
database of Ref. \cite{mrw1} and fit the ETH model \cite{glmbg} to
the resulting data. The set of the parameter values of the ETH model, as well
as the predictions derived on their basis for the hadronic phase shifts and for
the low-energy constants, are significantly different from the results
obtained in the analysis of the truncated elastic-scattering
databases. The main difference in the hadronic phase shifts occurs in
. We discuss the implications of these findings in
terms of the violation of the isospin invariance in the hadronic part of the
interaction. The effect observed amounts to the level of in the
CX scattering amplitude below 70 MeV. The results and conclusions of this study
agree well with those obtained in the mid 1990s, when the isospin invariance
was first tested by using experimental data, and disagree with the
predictions obtained within the framework of the heavy-baryon
Chiral-Perturbation Theory
Comments on a monetarist approach to demand management
Monetary policy ; Macroeconomics
A comparative static analysis of some monetarist propositions
Monetary policy ; Fiscal policy
Identification of dynamic economic models from reduced form VECM structures: an application of covariance restrictions
This analysis is a straightforward implementation of both long-run and short-run identifying or overidentifying restrictions on a vector error correction model in the "structural VAR" framework. The framework utilizes covariance restrictions, long-run multiplier restrictions, error correction coefficient restrictions, and restrictions on slope coefficients of the stimultaneous interactions in the "economic model." The framework is general enough to incorporate restrictions on impact multipliers. Two examples are provided. The first example is a dynamic M2 demand specification with a comparison to previous results that are constructed using restrictions on distributed lag coefficients to achieve identification. The second example illustrates the identification of equilibrium short-term and long-term interest responses of money demand using error-correction coefficient restrictions when the individual coefficients are underidentified in the cointegrating vectors in the presence of stationary interest rate spreads.Econometric models ; Demand for money
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