25,938 research outputs found
Is there an Ay problem in low-energy neutron-proton scattering?
We calculate Ay in neutron-proton scattering for the interactions models
WJC-1 and WJC-2 in the Covariant Spectator Theory. We find that the recent 12
MeV measurements performed at TUNL are in better agreement with our results
than with the Nijmegen Phase Shift Analysis of 1993, and after reviewing the
low-energy data, conclude that there is no Ay problem in low-energy np
scattering.Comment: 5 pages, 2 figures, accepted by PL
Universality of 2d Yukawa and Gross-Neveu models
Evidence for the same universal behavior of 2d Yukawa and Gross-Neveu models
in a certain range of couplings, particularly for , is presented.Comment: 3 pages compressed uuencoded PostScript, to appear in the Proceedings
of LATTICE '93 (Dallas), HLRZ 91/9
Social fund support of microfinance : a review of implementation experience
The case studies were developed in order to help Bank task team leaders, and their client country counterparts, design and support effective microfinance components, within social funds. The case studies aim to highlight best practice, as well as challenges for designing, and implementing a microfinance component within a multi-sectoral project. Based on lessons learned from these case studies, a set of guidelines were developed, available from the Social Protection Advisory Service, or the Social Funds website.Banks&Banking Reform,Rural Finance,Private Participation in Infrastructure,Agricultural Research,Microfinance
The influence of negative-energy states on proton-proton bremsstrahlung
We investigate the effect of negative-energy states on proton-proton
bremsstrahlung using a manifestly covariant amplitude based on a T-matrix
constructed in a spectator model. We show that there is a large cancellation
among the zeroth-order, single- and double-scattering diagrams involving
negative-energy nucleonic currents. We thus conclude that it is essential to
include all these diagrams when studying effects of negative-energy states.Comment: 12 pages revtex and 3 figure
Deconfinement transition in 2+1-dimensional SU(4) lattice gauge theory
A missing piece is added to the Svetitsky-Yaffe conjecture. The spin model in
the same universality class as the (2+1)d SU(4) theory, the 2d Ashkin-Teller
model, has a line of continuously varying critical exponents. The exponents
measured in the gauge theory correspond best to the Potts point on the
Ashkin-Teller line.Comment: Lattice2003(topology), 3 pages, 5 figure
Relativistic tunneling through opaque barriers
We propose an analytical study of relativistic tunneling through opaque
barriers. We obtain a closed formula for the phase time. This formula is in
excellent agreement with the numerical simulations and corrects the standard
formula obtained by the stationary phase method. An important result is found
when the upper limit of the incoming energy distribution coincides with the
upper limit of the tunneling zone. In this case, the phase time is proportional
to the barrier width.Comment: 11 pages, 3 figure
Thermodynamics of rotating self-gravitating systems
We investigate the statistical equilibrium properties of a system of
classical particles interacting via Newtonian gravity, enclosed in a
three-dimensional spherical volume. Within a mean-field approximation, we
derive an equation for the density profiles maximizing the microcanonical
entropy and solve it numerically. At low angular momenta, i.e. for a slowly
rotating system, the well-known gravitational collapse ``transition'' is
recovered. At higher angular momenta, instead, rotational symmetry can
spontaneously break down giving rise to more complex equilibrium
configurations, such as double-clusters (``double stars''). We analyze the
thermodynamics of the system and the stability of the different equilibrium
configurations against rotational symmetry breaking, and provide the global
phase diagram.Comment: 12 pages, 9 figure
Large-N limit of the two-dimensinal Non-Local Yang-Mills theory on arbitrary surfaces with boundary
The large-N limit of the two-dimensional non-local U Yang-Mills theory
on an orientable and non-orientable surface with boundaries is studied. For the
case which the holonomies of the gauge group on the boundaries are near the
identity, , it is shown that the phase structure of these theories
is the same as that obtain for these theories on orientable and non-orientable
surface without boundaries, with same genus but with a modified area
.Comment: 10 pages, no figure
A new large N phase transition in YM2
Inspired by the interpretation of two dimensional Yang-Mills theory on a
cylinder as a random walk on the gauge group, we point out the existence of a
large N transition which is the gauge theory analogue of the cutoff transition
in random walks. The transition occurs in the strong coupling region, with the
't Hooft coupling scaling as alpha*log(N), at a critical value of alpha (alpha
= 4 on the sphere). The two phases below and above the transition are studied
in detail. The effective number of degrees of freedom and the free energy are
found to be proportional to N^(2-alpha/2) below the transition and to vanish
altogether above it. The expectation value of a Wilson loop is calculated to
the leading order and found to coincide in both phases with the strong coupling
value.Comment: 23 pages, 3 figure
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