41,019 research outputs found
Maximal variance reduction for stochastic propagators with applications to the static quark spectrum
We study a new method -- maximal variance reduction -- for reducing the
variance of stochastic estimators for quark propagators. We find that while
this method is comparable to usual iterative inversion for light-light mesons,
a considerable improvement is achieved for systems containing at least one
infinitely heavy quark. Such systems are needed for heavy quark effective
theory. As an illustration of the effectiveness of the method we present
results for the masses of the ground state and excited states of
mesons and baryons. We compare these results with the experimental
spectra involving quarks.Comment: 31 pages with 7 postscript file
Development of a versatile laser light scattering instrument
A versatile laser light scattering (LLS) instrument is developed for use in microgravity to measure microscopic particles of 30 A to above 3 microns. Since it is an optical technique, LLS does not affect the sample being studied. A LLS instrument built from modules allows several configurations, each optimized for a particular experiment. The multiangle LLS instrument can be mounted in the rack in the Space Shuttle and on Space Station Freedom. It is possible that a Space Shuttle glove-box and a lap-top computer containing a correlator card can be used to perform a number of experiments and to demonstrate the technology needed for more elaborate investigations. This offers simple means of flying a great number of experiments without the additional requirements of full-scale flight hardware experiments
Unconventional magnetism in the 4d based () honeycomb system AgLiRuO
We have investigated the thermodynamic and local magnetic properties of the
Mott insulating system AgLiRuO containing Ru
(4) for novel magnetism. The material crystallizes in a monoclinic
structure with RuO octahedra forming an edge-shared
two-dimensional honeycomb lattice with limited stacking order along the
-direction. The large negative Curie-Weiss temperature ( = -57
K) suggests antiferromagnetic interactions among Ru ions though magnetic
susceptibility and heat capacity show no indication of magnetic long-range
order down to 1.8 K and 0.4 K, respectively. Li nuclear magnetic
resonance (NMR) shift follows the bulk susceptibility between 120-300 K and
levels off below 120 K. Together with a power-law behavior in the temperature
dependent spin-lattice relaxation rate between 0.2 and 2 K, it suggest dynamic
spin correlations with gapless excitations. Electronic structure calculations
suggest an description of the Ru-moments and the possible importance of
further neighbour interactions as also bi-quadratic and ring-exchange terms in
determining the magnetic properties. Analysis of our SR data indicates
spin freezing below 5 K but the spins remain on the borderline between static
and dynamic magnetism even at 20 mK.Comment: 10 pages, 11 figures. accepted in Phys. Rev.
Resonating valence-bond physics on the honeycomb lattice
We study bond and spin correlations of the nearest-neighbour resonating
valence bond (RVB) wavefunction for a SU() symmetric antiferromagnet
on the honeycomb lattice. We find that spin correlations in this wavefunction
are short-ranged, while the bond energy correlation function takes on an
oscillatory power-law form , where is the
wavevector corresponding to "columnar" valence-bond solid order on the
honeycomb lattice, and . We use a recently
introduced large- expansion approach to relate bond-energy correlators of
the SU() wavefunction to dimer correlations of an interacting fully-packed
dimer model with a three-dimer interaction of strength .
Putting , we find numerically that the dimer correlation function
of this dimer model has power-law behaviour with , in rather good agreement with the wavefunction results. We
also study the same quantities for and find that the bond-energy
correlations in the SU() wavefunction are consistently well-reproduced by
the corresponding dimer correlations in the interacting dimer model.Comment: 10 pages; two-column prb format; 14 .eps figures; v2: version
submitted to PRB; v3: published versio
Dual Superconductor Scenario of Confinement: A Systematic Study of Gribov Copy Effects
We perform a study of the effects from maximal abelian gauge Gribov copies in
the context of the dual superconductor scenario of confinement, on the basis of
a novel approach for estimation of systematic uncertainties from incomplete
gauge fixing. We present numerical results, in SU(2) lattice gauge theory,
using the overrelaxed simulated annealing gauge fixing algorithm. We find
abelian and non-abelian string tensions to differ significantly, their ratio
being 0.92(4) at BETA = 2.5115. An approximate factorization of the abelian
potential into monopole and photon contributions has been confirmed, the former
giving rise to the abelian string tension.Comment: 35 pages uucompressed LaTeX with 10 encapsuled postscript figure
Stripes: Why hole rich lines are antiphase domain walls?
For stripes of hole rich lines in doped antiferromagnets, we investigate the
competition between anti-phase and in-phase domain wall ground state
configurations. We argue that a phase transition must occure as a function of
the electron/hole filling fraction of the domain wall. Due to {\em transverse}
kinetic hole fluctuations, empty domain walls are always anti-phase. At
arbitrary electron filling fraction () of the domain wall (and in
particular for as in LaNdSrCuO), it is essential to
account also for the transverse magnetic interactions of the electrons and
their mobility {\em along} the domain wall.
We find that the transition from anti-phase to in-phase stripe domain wall
occurs at a critical filling fraction , for any value of
. We further use our model to estimate the spin-wave
velocity in a stripe system. Finally, relate the results of our microscopic
model to previous Landau theory approach to stripes.Comment: 11 pages, 3 figure
Block Analysis for the Calculation of Dynamic and Static Length Scales in Glass-Forming Liquids
We present {\it block analysis}, an efficient method to perform finite-size
scaling for obtaining the length scale of dynamic heterogeneity and the
point-to-set length scale for generic glass-forming liquids. This method
involves considering blocks of varying sizes embedded in a system of a fixed
(large) size. The length scale associated with dynamic heterogeneity is
obtained from a finite-size scaling analysis of the dependence of the
four-point dynamic susceptibility on the block size. The block size dependence
of the variance of the -relaxation time yields the static point-to-set
length scale. The values of the obtained length scales agree quantitatively
with those obtained from other conventional methods. This method provides an
efficient experimental tool for studying the growth of length scales in systems
such as colloidal glasses for which performing finite-size scaling by carrying
out experiments for varying system sizes may not be feasible.Comment: 5 pages, 3 figure
Scattering of the double sine-Gordon kinks
We study the scattering of kink and antikink of the double sine-Gordon model.
There is a critical value of the initial velocity of the colliding
kinks, which separates different regimes of the collision. At
we observe kinks reflection, while at their interaction is
complicated with capture and escape windows. We obtain the dependence of
on the parameter of the model. This dependence possesses a series of
local maxima, which has not been reported by other authors. At some initial
velocities below the critical value we observe a new phenomenon -- the escape
of two oscillons in the final state. Besides that, at we found
the initial kinks' velocities at which the oscillons do not escape, and the
final configuration looks like a bound state of two oscillons.Comment: 12 pages, 7 figures; v2: minor changes to match version published in
EPJ
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