Lorentz gauge and Gribov ambiguity in the compact lattice U(1) theory
The Gribov ambiguity problem is studied for compact U(1) lattice theory within the Lorentz gauge. In the Coulomb phase, it is shown that apart from double Dirac sheets all gauge (i.e. Gribov) copies originate mainly from the zero-momentum modes of the gauge fields. The removal of the zero–momentum modes turns out to be necessary for reaching the absolute maximum of the gauge functional F(θ) . A new gauge fixing procedure – zero-momentum Lorentz gauge – is proposed.
Monopoles and Dirac sheets in compact U(1) lattice gauge theory
Abstract We point out that in compact U(1) lattice gauge theory on a finite volume, some topological excitations (monopole loops and Dirac sheets winding through the lattice) effectively divide the configuration space in separate sectors. Local Monte Carlo algorithms have problems in moving from one such sector to another and may thus produce misleading results. We have observed this phenomenon in two independent programs, one for the Z(128) subgroup and Villain's action near the phase transition, the other for Z(32) and Wilson's action in the cold phase.
5.63 and 5.80 MeV levels of Ne20; de-excitation branching
Abstract The ratio Г γ /Г for the 5.63 and 5.80 MeV levels of Ne 20 has been determined to be 0.077 (±0.008) and −4 , respectively, by using the C 12 (C 12 , α)Ne 20 reaction and determining the fraction of the events in which the alpha-particle and the Ne 20 recoil are present in coincidence at the kinematically correct angles. In both cases these results in themselves are shown to imply radiative E1 transition (5.63→1.63 and 5.80→0, respectively) probabilities ⪡5 × 10 −5 Weisskopf units. When taken together with the life-time for the 5.63 MeV level measured by Evans et al . values of Г( E1 ) ≲ 5 × 10 −6 and Г α ≈ 6% of the particle estimate are obtained for this state.