The calculation of critical amplitudes in SU(2) lattice gauge theory
We calculate the critical amplitudes of the Polyakov loop and its susceptibility at the deconfinement transition of (3 + 1)-dimensional SU(2) gauge theory. To this end we study the corrections due to irrelevant exponents in the scaling functions. As a guiding line for determining the critical amplitudes we use envelope equations which we derive from the finite site scaling formulae of the observables. We have produced new high precision data on N-sigma(3) x 4 lattices for N-sigma = 12, 18, 26 and 36, With these data we find different corrections to the asymptotic scaling behaviour above and below the transition. Our result for the universal ratio of the susceptibility amplitudes is C+/C- = 4.72(11) and thus in excellent agreement with a recent measurement for the 3d Ising model. (C) 1999 Published by Elsevier Science B.V.
Universal amplitude ratios from numerical studies of the three-dimensional O(2) model
We investigate the three-dimensional O(2) model near the critical point by Monte Carlo simulations and calculate the major universal amplitude ratios of the model. The ratio U0 = A+/A− is determined directly from the specific heat data at zero magnetic field. The data do not, however, allow us to extract an accurate estimate for α. Instead, we establish a strong correlation of U0 with the value of α used in the fit. This numerical α-dependence is given by A+/A+ = 1 − 4.20(5)α + O(α2). For the special α-values used in other calculations, we find full agreement with the corresponding ratio values, e.g. that of the shuttle experiment with liquid helium. On the critical isochore, we obtain the ratio ξ+/ξ−T = 0.293(9), and on the critical line the ratio ξcT/ξcL = 1.957(10) for the amplitudes of the transverse and longitudinal correlation lengths. These two ratios are independent of the α- or ν-values used here.
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.