Potts correlators and the static three-quark potential
We discuss the two- and three-point correlators in the two-dimensional three-state Potts model in the high temperature phase of the model. By using the form factor approach and perturbed conformal field theory methods we are able to describe both the large distance and the short distance behaviours of the correlators. We compare our predictions with a set of high precision Monte Carlo simulations (performed on the triangular lattice realization of the model) finding a complete agreement in both regimes. In particular we use the two-point correlators to fix the various non-universal constants involved in the comparison (whose determination is one of the results of our analysis) and then use these constants to compare numerical results and theoretical predictions for the three-point correlator with no free parameter. Our results can be used to shed some light on the behaviour of the three-quark correlator in the confining phase of the (2 + 1)-dimensional SU(3) lattice gauge theory which is related by dimensional reduction to the three-spin correlator in the high temperature phase of the three-state Potts model. The picture which emerges is that of a smooth crossover between a Δ-type law at short distances and a Y-type law at large distances.

title: Monte Carlo Overrelaxation for SU(N) Gauge Theories
abstract: The standard approach to Monte Carlo simulations of SU(N) Yang-Mills theories updates successive SU(2) subgroups of each SU(N) link. We follow up on an old proposal of Creutz, to perform overrelaxation in the full SU(N) group instead, and show that it is more efficient.

title: The baryon static potential from lattice QCD
abstract: Lattice QCD simulations offer the possibility of determining the potential between three static quarks from first principles. We review the status of such simulations, and the relative standing of the two theoretical proposals for the baryonic potential: the Delta law (sum of two-body terms) and the Y law (length of three flux strings joined together at a junction). We also present new results on the leading Luscher-like corrections to the asymptotic linear potential.

title: Chiral fermions on the lattice
abstract: We discuss topological obstructions to putting chiral fermions on an even-dimensional lattice. The setting includes Ginsparg–Wilson fermions, but is more general. We prove a theorem which relates the total chirality to the difference of generalised winding numbers of chiral projection operators. For an odd number of Weyl fermions this implies that particles and anti-particles live in topologically different spaces.

title: The ground state of three quarks
abstract: We measure the static three-quark potential in SU(3) lattice gauge theory with improved accuracy, by using all available technical refinements, including Luscher-Weisz exponential variance reduction. Together with insight gained from 3-state Potts model simulations, our results allow us to sort out the merits of the Delta- and Y-ansaetze.

title: SO(3) Versus SU(2)Lattice Gauge Theory
abstract: We consider the SO (3) lattice gauge theory at weak coupling, in the Villain action. We exhibit an analytic path in coupling space showing the equivalence of the SO (3) theory with SU (2) summed over all twist sectors. This clarifies the “mysterious phase” of SO (3). As order parameter, we consider the dual string tension or center vortex free energy, which we measure in SO (3) using multicanonical Monte Carlo. This allows us to set the scale, indicating that O(700)4 lattices are necessary to probe the confined phase. We consider the relevance of our findings for confinement in other gauge groups with trivial center.

title: STATUS OF THE GDH EXPERIMENT ON THE DEUTERON AT MAMI

title: Beam-helicity asymmetries in double-pion photoproduction off the proton.
abstract: Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels gamma[over -->]p-->pi(+)pi(0)n, gamma[over -->]p-->pi(0)pi(0)p, and gamma[over -->]p-->pi(+)pi(-)p. The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of pi(0) mesons were detected in a 4pi electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction dynamics.

title: Study of the gamma p --> pi0 pi0 p reaction with the Crystal Ball/TAPS at the Mainz
abstract: The gamma p --> pi0 pi0 p reaction has been measured from threshold to 1.4 GeV using the Crystal Ball and TAPS photon spectrometers together with the photon tagging facility at the Mainz Microtron. The experimental results include total and differential cross sections as well as specific angular distributions, which were used to extract partial-wave amplitudes. In particular, the energy region below the D13(1520) resonance was studied.

title: Study of the $\gamma p -> \eta p$ reaction with the Crystal Ball detector at the Mainz Microtron(MAMI-C)
abstract: Here we correct a factor of 2 missed in one of figures and the corresponding sentence in the text. It does not change any conclusions.

title: Compton scattering from the free and bound proton at backward angles above π-threshold
abstract: Differential cross sections for Compton scattering from the free proton at Theta(gamma)(lab) = 130.7 degrees in the energy region from 200 MeV to 410 MeV and far quasi-free Compton scattering from the proton bound in the deuteron at Theta(gamma)(lab) = 148.8 degrees in the energy region from 200 MeV to 290 MeV have been measured. The free proton data are in agreement with dispersion-theory predictions based on standard parameters. The difference of the proton polarizabilities has been extracted from the quasi-free data. Our result, - = [9.1 +/- 1.7(stat + syst) +/- 1.2(mod)] x 10(-4) fm(3), is in reasonable agreement with the world average of the free proton data if the backward spin polarizability gamma(pi) is taken to be -37.6 x 10(-4) fm(4) as predicted by dispersion theory in agreement with many theoretical calculations. This implies that quasi-free Compton scattering may also be used to determine the electromagnetic polarizabilities of the neutron. No indication has been found of a recently suggested new contribution to gamma(pi).