3,601 research outputs found
Chiral Dynamics of Deeply Bound Pionic Atoms
We present and discuss a systematic calculation, based on two-loop chiral
perturbation theory, of the pion-nuclear s-wave optical potential. A proper
treatment of the explicit energy dependence of the off-shell pion self-energy
together with (electromagnetic) gauge invariance of the Klein-Gordon equation
turns out to be crucial. Accurate data for the binding energies and widths of
the 1s and 2p levels in pionic ^{205}Pb and ^{207}Pb are well reproduced, and
the notorious "missing repulsion" in the pion-nuclear s-wave optical potential
is accounted for. The connection with the in-medium change of the pion decay
constant is clarified.Comment: preprint ECT*-02-16, 4 pages, 3 figure
A Model of Russia's "Virtual Economy"
The Russian Economy has evolved into a hybrid form, a partially monetized quasi-market system that has been called the virtual economy. In the virtual economy, barter and non-monetary transactions play a key role in transferring value from the productive activities to the loss-making sectors of the economy. We show how this transfer takes place, and how it can be consistent with the incentives of economic agents. We analyze a simple partial-equilibrium model of the virtual economy, and show how it might prove an obstacle to industrial restructuring and hence marketizing transition.http://deepblue.lib.umich.edu/bitstream/2027.42/39701/3/wp317.pd
Isospin breaking in pion-nucleon scattering at threshold by radiative processes
We investigate the dispersive contribution by radiative processes such as
(pi- proton to neutron gamma) and (pi- proton to Delta gamma) to the
pion-nucleon scattering lengths of charged pions in the heavy baryon limit.
They give a large isospin violating contribution in the corresponding isoscalar
scattering length, but only a small violation in the isovector one. These terms
contribute 6.3(3)% to the 1s level shift of pionic hydrogen and give a chiral
constant F_pi^2f_1=-25.8(8) MeV.Comment: 9 pages with 1 figur
Evaluation of the scattering amplitude in the -channel at finite density
The scattering amplitude in the -channel is studied at
finite baryonic density in the framework of a chiral unitary approach which
successfully reproduces the meson meson phase shifts and generates the
and resonances in vacuum. We address here a new variety of mechanisms
recently suggested to modify the interaction in the medium, as well as
the role of the wave selfenergy, in addition to the wave, in the
dressing of the pion propagators.Comment: 26 pages, 17 figure
Precision determination of the pi-N scattering lengths and the charged pi-NN coupling constant
We critically evaluate the isovector GMO sumrule for the charged
coupling constant using recent precision data from p and d atoms
and with careful attention to systematic errors. From the d scattering
length we deduce the pion-proton scattering lengths (statistic) (systematic))~ and . From this a direct evaluation gives (statistic)(systematic) or .Comment: 4 pages, 1 figure, latex and postscript; invited talk at PANIC99; to
appear in Nucl. Phys. A; changed notation: g^2 and f^2 replaced by
conventional g^2/4\pi and f^2/4\p
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Restructuring an Industry During Transition: A Two-Period Model
This paper develops the two-period model of enterprise shutdown during transition that was introduced in Ericson (1994). Its purpose is to provide a formal basis for the study of what Kornai (1994) has called the "transformation of the real structure of the economy" during the transition process. It focuses at the industry level of restructuring, taking a normative, industrial policy, perspective
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The Stuctural Barrier to Transition: A Note on Input-Output Tables of Centrally Planned Economies
This note begins an exploration of one of the key legacies of the Soviet economic system, the physical structure of production and economic interaction, and its impact on the transition to a market-based system. It addresses some reasons for the size of the "shock" to the economy subsequent to the liberalization of prices, including the apparent disappearance of vast amounts of industrial output and an inflation driven by more than just monetary factors
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