3,705 research outputs found
Chiral dynamics of the nuclear equation of state
We present a new chiral power expansion scheme for the nuclear equation of
state. The scheme is effective in the sense that it is constructed to work
around nuclear saturation density. The leading and subleading terms are
evaluated and are shown to provide an excellent equation of state. As a further
application we considered the chiral quark condensate in nuclear matter.
Already at nuclear saturation density we predict a substantially smaller
reduction of the condensate as compared to conventional approaches.Comment: 7 pages, 4 figures, talk given at: "QCD at Finite Baryon Density",
Bielefeld (April 1998
Price Convergence under EMU? First Estimates
This paper examines whether European monetary union has lowered the degree of price dispersion among member countries. A number of different estimation methods are applied to four independent datasets containing prices of identical goods. While the results reported in the paper vary somewhat across goods, they provide little overall support of the European Commission's claim that the single currency would significantly deepen market integration among the euro-zone countries. Even though this should be viewed as preliminary evidence, it does suggest that there are other, more important impediments to market integration in the EU.price convergence, EMU, treatment effect
Aid, Governance, and Private Foreign Investment: Some Puzzling Findings and a Possible Explanation
Does offcial aid pave the road for private foreign investment or does it suffocate private initiative by diverting resources towards unproductive activities? In this paper we explore this question using data for a large number of developing and emerging economies. Controlling for countries’ institutional environment, we find that, evaluated at the mean, the marginal effect of aid on private foreign investment is close to zero. Surprisingly, however, the effect is strictly positive for countries in which private agents face a substantial regulatory burden. After testing the robustness of this result, we offer a theoretical model that is able to rationalize our puzzling observation.
The Macroeconomic Effects of Foreign Aid: A Survey
Research on the macroeconomic effects of aid has expanded rapidly in recent years. In this paper, we provide a survey of this literature. We start by reviewing some theoretical models that suggest a positive impact of aid on investment and growth. We then discuss the empirical evidence, giving particular attention to the role of institutions and policies in determining aid effectiveness. As a general conclusion, we suggest adopting a more disaggregate perspective with respect both to different types of aid and to various aspects of governance.foreign aid, economic growth, institutions, governance
Study of the threshold behavior of the N scattering amplitude through the associated photoproduction of - and -mesons
We suggest that the reaction cross section, in the
kinematics where the invariant mass in the final state lies between
the threshold value (m+m) and the N*(1535) resonance mass, is
largely determined by the scattering amplitude close to threshold. The
initial photon energy is chosen in the range GeV, in
order to reach low (absolute) values of the squared 4-momentum transfer from
the initial photon to the final -meson. In these conditions, we expect
the t-channel - and -meson exchanges to drive the dynamics
underlying the process. We show that the
-exchange is the dominating contribution to the cross section while the
-exchange is negligible. The - interference is of the order
of . The sign of this term is not known and alters significantly our
results. Data on the process would be therefore very
useful to help unravelling the behavior of the scattering amplitude
close to threshold and assessing the possibility of producing -nucleus
bound states.Comment: 8 pages, 6 figures, Invited talk at MESON 2006, June 9th-13th, 2006,
Cracow (Poland
e+e- pair production from nucleon targets in the resonance region
We present consistent theoretical descriptions of the
and reactions on proton and neutron targets for total
center of mass energies ranging between 1.50 GeV and 1.75 GeV. These
reactions are complementary to study the coupling of low-lying baryon
resonances to vector meson-nucleon channels. We show in particular how the
resonant structure of the amplitudes for both processes generates specific and
large quantum interferences between - and -meson decays into
pairs. Data on the and
reactions are expected in the near future from the HADES program at GSI and
from dilepton studies with CLAS at JLab.Comment: 6 pages, 6 figures, Paper presented at Hirschegg 2004, 'Probing
nuclei and nucleons with electrons and photons', January 12th-16th, 200
On kinematical constraints in the hadrogenesis conjecture for the baryon resonance spectrum
We consider the reaction dynamics of bosons with negative parity and spin
or and fermions with positive parity and spin or
. Such systems are of central importance for the computation of
the baryon resonance spectrum in the hadrogenesis conjecture. Based on a chiral
Lagrangian the coupled-channel partial-wave scattering amplitudes have to be
computed. We study the generic properties of such amplitudes. A decomposition
of the various scattering amplitudes into suitable sets of invariant functions
expected to satisfy Mandelstam's dispersion-integral representation is
presented. Sets are identified that are free from kinematical constraints and
that can be computed efficiently in terms of a novel projection algebra. From
such a representation one can deduce the analytic structure of the partial-wave
amplitudes. The helicity and the conventional angular-momentum partial-wave
amplitudes are kinematically constrained at the Kibble conditions. Therefore an
application of a dispersion-integral representation is prohibitively
cumbersome. We derive covariant partial-wave amplitudes that are free from
kinematical constraints at the Kibble conditions. They correspond to specific
polynomials in the 4-momenta and Dirac matrices that solve the various
Bethe-Salpeter equations in the presence of short-range interactions
analytically.Comment: 18 page
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