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 $\kappa<0$, 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$(N)$ 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, $U\simeq I$, 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 $V+\hat{A}$.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