1,169 research outputs found
The three-loop beta function of SU(N) lattice gauge theories with Wilson fermions
We calculate the third coefficient of the lattice beta function associated
with the Wilson formulation for both gauge fields and fermions. This allows us
to evaluate the three-loop correction (linear in ) to the relation
between the lattice Lambda-parameter and the bare coupling , which is
important in order to verify asymptotic scaling predictions. Our calculation
also leads to the two-loop relation between the coupling renormalized in the
MSbar scheme and .
The original version of this paper contained a numerical error in one of the
diagrams, which has now been corrected. The calculations, as well as the layout
of the paper have remained identical, but there are some important changes in
the numerical results.Comment: One 14-page LaTeX file, one PostScript file containing 2 figures.
Corrected a numerical error in one of the diagrams. The calculations, as well
as the layout of the paper have remained unaffected, but there are some
important changes in the numerical result
Light Quark Mass Reweighting
We present a systematic study of the effectiveness of light quark mass
reweighting. This method allows a single lattice QCD ensemble, generated with a
specific value of the dynamical light quark mass, to be used to determine
results for other, nearby light dynamical quark masses. We study two gauge
field ensembles generated with 2+1 flavors of dynamical domain wall fermions
with light quark masses m_l=0.02 (m_\pi=620 MeV) and m_l=0.01 (m_\pi=420 MeV).
We reweight each ensemble to determine results which could be computed directly
from the other and check the consistency of the reweighted results with the
direct results. The large difference between the 0.02 and 0.01 light quark
masses suggests that this is an aggressive application of reweighting as can be
seen from fluctuations in the magnitude of the reweighting factor by four
orders of magnitude. Never-the-less, a comparison of the reweighed topological
charge, average plaquette, residual mass, pion mass, pion decay constant, and
scalar correlator between these two ensembles shows agreement well described by
the statistical errors. The issues of the effective number of configurations
and finite sample size bias are discussed. An examination of the topological
charge distribution implies that it is more favorable to reweight from heavier
mass to lighter quark mass.Comment: 24 pages and 10 figure
Topological Charge Membranes in 2D and 4D Gauge Theory
Local topological charge structure in the 2D CP(N-1) sigma models is studied
using the overlap Dirac operator. Long-range coherence of topological charge
along locally 1D regions in 2D space-time is observed. We discuss the
connection between these results and the recent discovery of coherent 3D sheets
of topological charge in 4D QCD. In both cases, coherent regions of topological
charge form along surfaces of approximmate codimension 1.Comment: Lattice2004(topology
NVV auger spectra from W(100)
The NVV Auger spectrum from a clean W(100) surface has been measured in the second derivative, d^2N (E)/dE^2, mode to enhance fine structure. This measurement is compared with spectra generated from both the selfâconvolution of the tungsten valenceâband bulk density of states (obtained from a relativistic APW energy band calculation) and a "restricted convolution" in which only transitions involving electrons from the same valence energy are allowed. The restricted convolution for a model of the Auger process in which both N_6VV and N_7VV transitions contribute offers the best match of theory and experiment. No distinct evidence of Auger emission involving the surface resonance present on W(100) is observed. Effects of H_2 and O_2 adsorption on the Auger spectrum of the W(100) surface are reported
Coexistence of pairing gaps in three-component Fermi gases
We study a three-component superfluid Fermi gas in a spherically symmetric
harmonic trap using the Bogoliubov-deGennes method. We predict a coexistence
phase in which two pairing field order parameters are simultaneously nonzero,
in stark contrast to studies performed for trapped gases using local density
approximation. We also discuss the role of atom number conservation in the
context of a homogeneous system.Comment: Text revised, added two figures and three reference
Quenching Effects in the Hadron Spectrum
Lattice QCD has generated a wealth of data in hadronic physics over the last
two decades. Until relatively recently, most of this information has been
within the "quenched approximation" where virtual quark--anti-quark pairs are
neglected. This review presents a descriptive discussion of the effects of
removing this approximation in the calculation of hadronic masses.Comment: To appear in "Lattice Hadron Physics", ed. A.C. Kalloniatis, D.B.
Leinweber and A.G. William
Wess-Zumino-Witten model off criticality
We study the renormalization group flow properties of the Wess-Zumino-Witten
model in the region of couplings between and , by
evaluating the two-loop Zamolodchikov's -function. We also discuss the
region of negative couplings.Comment: 8 page
Hadron Masses From Novel Fat-Link Fermion Actions
The hadron mass spectrum is calculated in lattice QCD using a novel fat-link
clover fermion action in which only the irrelevant operators in the fermion
action are constructed using smeared links. The simulations are performed on a
16^3 x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with
n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link
Irrelevant Clover (FLIC) action provides scaling which is superior to
mean-field improvement, and offers advantages over nonperturbative 0(a)
improvement, including a reduced exceptional configuration problem.Comment: 12 pages, 4 figures, new simulation with mean-field improved clover,
further discussion of actio
Non-monotonic current-to-rate response function in a novel integrate-and-fire model neuron
A novel integrate-and-fire model neuron is proposed to account for a non-monotonic f-I response function, as experimentally observed. As opposed to classical forms of adaptation, the present integrate- and-fire model the spike-emission process incorporates a state - dependent inactivation that makes the probability of emitting a spike decreasing as a function of the mean depolarization level instead of the mean firing rate. \ua9 Springer-Verlag Berlin Heidelberg 2002
Unquenched Charmonium with NRQCD - Lattice 2000
We present results from a series of NRQCD simulations of the charmonium
system, both in the quenched approximation and with n_f = 2 dynamical quarks.
The spectra show evidence for quenching effects of ~10% in the S- and
P-hyperfine splittings. We compare this with other systematic effects.
Improving the NRQCD evolution equation altered the S-hyperfine by as much as 20
MeV, and we estimate radiative corrections may be as large as 40%.Comment: Lattice 2000 (Heavy Quark Physics
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