1109052
Polyakov loop and its relation to static quark potentials and free energies
It appears well accepted in the literature that the correlator of Polyakov loops in a finite temperature system decays with the average free energy of the static quark-antiquark system and can be decomposed into singlet and adjoint (or octet for QCD) contributions. By fixing a gauge respecting the transfer matrix, attempts have been made to extract those contributions separately. In this paper we point out that the average and adjoint channels of Polyakov loop correlators are misconceptions. We show analytically that all channels receive contributions from singlet states only, and give a corrected definition of the singlet free energy. We verify this finding by simulations of the 3D SU(2) pure gauge theory in the zero-temperature limit, which allows one to cleanly extract the ground state exponents and the nontrivial matrix elements. The latter account for the difference between the channels observed in previous simulations.
119425676
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.
119453725
SO(3) Versus SU(2)Lattice Gauge Theory
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.
9746061
The ground state of three quarks
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.
15784128
Vortex free energies in SO(3) and SU(2) lattice gauge theory
Abstract Lattice gauge theories with gauge groups SO(3) and SU(2) are compared. The free energy of electric twist, an order parameter for the confinement- deconfinement transition which does not rely on centre-symmetry breaking, is measured in both theories. The results are used to calibrate the scale in SO(3).
16219757
Monte Carlo Overrelaxation for SU(N) Gauge Theories
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.
45543586
Neutron polarizabilities investigated by quasifree Compton scattering from the deuteron.
Measuring Compton scattered photons and recoil neutrons in coincidence, quasifree Compton scattering by the neutron has been investigated at MAMI (Mainz) at theta(lab)(gamma) = 136 degrees in an energy range from 200 to 400 MeV. From the data a polarizability difference of alpha(n)-beta(n) = 9.8+/-3.6(stat)+2.1-1.1(syst)+/-2.2(model) in units of 10(-4) fm(3) has been determined. In combination with the polarizability sum alpha(n)+beta(n) = 15.2+/-0.5 deduced from photoabsorption data, the first precise results for the neutron electric and magnetic polarizabilities, alpha(n) = 12.5+/-1.8(stat)+1.1-0.6(syst)+/-1.1(model) and beta(n) = 2.7-/+1.8(stat)+0.6-1.1(syst)-/+1.1(model), are obtained.
119237531
Study of the gamma p --> pi0 pi0 p reaction with the Crystal Ball/TAPS at the Mainz
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.
8301422
Beam-helicity asymmetries in double-pion photoproduction off the proton.
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.
123062087
Compton scattering from the free and bound proton above π-threshold
The differential cross sections for Compton scattering from the proton have been measured at MAMI with three different detector setups. There is a good agreement among all the results. The theoretical calculation based on dispersion relations shows that there is no drastic change necessary in the parameters of this approach.
121815841
STATUS OF THE GDH EXPERIMENT ON THE DEUTERON AT MAMI