5,029 research outputs found
Polyakov loop and spin correlators on finite lattices A study beyond the mass gap
We derive an analytic expression for point-to-point correlation functions of
the Polyakov loop based on the transfer matrix formalism. For the Ising
model we show that the results deduced from point-point spin correlators are
coinciding with those from zero momentum correlators. We investigate the
contributions from eigenvalues of the transfer matrix beyond the mass gap and
discuss the limitations and possibilities of such an analysis. The finite size
behaviour of the obtained Ising model matrix elements is examined. The
point-to-point correlator formula is then applied to Polyakov loop data in
finite temperature gauge theory. The leading matrix element shows all
expected scaling properties. Just above the critical point we find a Debye
screening mass , independent of the volume.Comment: 13 pages and 8 figures, late
OH 12.8-0.9: A New Water-Fountain Source
We present observational evidence that the OH/IR star OH 12.8-0.9 is the
fourth in a class of objects previously dubbed "water-fountain" sources. Using
the Very Long Baseline Array, we produced the first images of the water maser
emission associated with OH 12.8-0.9. We find that the masers are located in
two compact regions with an angular separation of ~109 mas on the sky. The axis
of separation between the two maser regions is at a position angle of 1.5 deg.
East of North with the blue-shifted (-80.5 to -85.5 km/s) masers located to the
North and the red-shifted (-32.0 to -35.5 km/s) masers to the South. In
addition, we find that the blue- and red-shifted masers are distributed along
arc-like structures ~10-12 mas across oriented roughly perpendicular to the
separation axis. The morphology exhibited by the water masers is suggestive of
an axisymmetric wind with the masers tracing bow shocks formed as the wind
impacts the ambient medium. This bipolar jet-like structure is typical of the
three other confirmed water-fountain sources. When combined with the previously
observed spectral characteristics of OH 12.8-0.9, the observed spatio-kinematic
structure of the water masers provides strong evidence that OH 12.8-0.9 is
indeed a member of the water-fountain class.Comment: 12 pages, 2 figures (1 color), accepted for publication in the Ap J
Letter
Limitations to Carrier Mobility and Phase-Coherent Transport in Bilayer Graphene
We present transport measurements on high-mobility bilayer graphene fully
encapsulated in hexagonal boron nitride. We show two terminal quantum Hall
effect measurements which exhibit full symmetry broken Landau levels at low
magnetic fields. From weak localization measurements, we extract gate-tunable
phase coherence times as well as the inter- and intra-valley
scattering times and . While is in qualitative
agreement with an electron-electron interaction mediated dephasing mechanism,
electron spin-flip scattering processes are limiting at low
temperatures. The analysis of and points to local strain
fluctuation as the most probable mechanism for limiting the mobility in
high-quality bilayer graphene
A Study of Finite Temperature Gauge Theory in (2+1) Dimensions
We determine the critical couplings and the critical exponents of the finite
temperature transition in SU(2) and SU(3) pure gauge theory in (2+1)
dimensions. We also measure Wilson loops at on a wide range of
values using APE smearing to improve the signal. We extract the string tension
from a fit to large distances, including a string fluctuation term.
With these two entities we calculate .Comment: Talk presented at LATTICE96(finite temperature), not espcrc2 style: 7
pages, 4 ps figures, 22 k
Staggered Fermion Actions with Improved Rotational Invariance
We introduce a class of improved actions for staggered fermions which to
O(p^4) and O(p^6), respectively, lead to rotationally invariant propagators. We
discuss the resulting reduction of flavour symmetry breaking in the meson
spectrum and comment on the improvement in the calculation of thermodynamic
observables.Comment: 3 pages and 4 figures, Contribution to Lattice 97 (Poster Session),
late
Critical behaviour and scaling functions of the three-dimensional O(6) model
We numerically investigate the three-dimensional O(6) model on 12^3 to 120^3
lattices within the critical region at zero magnetic field, as well as at
finite magnetic field on the critical isotherm and for several fixed couplings
in the broken and the symmetric phase. We obtain from the Binder cumulant at
vanishing magnetic field the critical coupling J_c=1.42865(3). The universal
value of the Binder cumulant at this point is g_r(J_c)=-1.94456(10). At the
critical coupling, the critical exponents \gamma=1.604(6), \beta=0.425(2) and
\nu=0.818(5) are determined from a finite-size-scaling analysis. Furthermore,
we verify predicted effects induced by massless Goldstone modes in the broken
phase. The results are well described by the perturbative form of the model's
equation of state. Our O(6)-result is compared to the corresponding Ising, O(2)
and O(4) scaling functions. Finally, we study the finite-size-scaling behaviour
of the magnetisation on the pseudocritical line.Comment: 13 pages, 20 figures, REVTEX, fixed an error in the determination of
R_\chi and changed the corresponding line in figure 13
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