783 research outputs found
Variants of fattening and flavor symmetry restoration
We study the effects of different "fat link" actions for Kogut-Susskind
quarks on flavor symmetry breaking. Our method is mostly empirical - we compute
the pion spectrum with different valence quark actions on common sets of sample
lattices. Different actions are compared, as best we can, at equivalent
physical points. We find significant reductions in flavor symmetry breaking
relative to the conventional or to the "link plus staple" actions, with a
reasonable cost in computer time. We also develop and test a scheme for
approximate unitarization of the fat links. While our tests have concentrated
on the valence quark action, our results will be useful in designing
simulations with dynamical quarks.Comment: 16 pages, LaTeX, PostScript figures include
Glueball plus Pion Production in Photon-Photon Collisions.
We here compute the reaction
for various glueball candidates and their assumed quantum states, using a
non-relativistic gluon bound-state model for the glueball.Comment: To appear in Zeit. fur Phys. C; Plain Latex file, 16 pages; 5 figures
appended as a uuencoded postscript file
Heavy Quarks on Anisotropic Lattices: The Charmonium Spectrum
We present results for the mass spectrum of mesons simulated on
anisotropic lattices where the temporal spacing is only half of the
spatial spacing . The lattice QCD action is the Wilson gauge action plus
the clover-improved Wilson fermion action. The two clover coefficients on an
anisotropic lattice are estimated using mean links in Landau gauge. The bare
velocity of light has been tuned to keep the anisotropic, heavy-quark
Wilson action relativistic. Local meson operators and three box sources are
used in obtaining clear statistics for the lowest lying and first excited
charmonium states of , , , and . The
continuum limit is discussed by extrapolating from quenched simulations at four
lattice spacings in the range 0.1 - 0.3 fm. Results are compared with the
observed values in nature and other lattice approaches. Finite volume effects
and dispersion relations are checked.Comment: 36 pages, 6 figur
TASI Lectures on the Cosmological Constant
The energy density of the vacuum, Lambda, is at least 60 orders of magnitude
smaller than several known contributions to it. Approaches to this problem are
tightly constrained by data ranging from elementary observations to precision
experiments. Absent overwhelming evidence to the contrary, dark energy can only
be interpreted as vacuum energy, so the venerable assumption that Lambda=0
conflicts with observation. The possibility remains that Lambda is
fundamentally variable, though constant over large spacetime regions. This can
explain the observed value, but only in a theory satisfying a number of
restrictive kinematic and dynamical conditions. String theory offers a concrete
realization through its landscape of metastable vacua.Comment: 39 pages, 3 figure
Cohort profile: The Trivandrum Non-alcoholic Fatty Liver Disease (NAFLD) Cohort
Purpose The Trivandrum NAFLD cohort is a population-based study designed to examine the interaction between genetic and lifestyle factors and their association with increased risk of NAFLD within the Indian population. Participants Between 2013 and 2016, 2222 participants were recruited to this cohort through multi-stage cluster sampling across the whole population of Trivandrum â a district within the state of Kerala, South India. Data was collected from all inhabitants of randomly-selected households over the age of 25. Findings to date Full baseline clinical and pathological data was collected from 2158 participants. This included detailed demographic profiles, anthropometric measures and lifestyle data (food frequency, physical activity and anxiety and depression questionnaires). Biochemical profile and ultrasound assessment of the liver were performed and whole blood aliquots were collected for DNA analysis. The NAFLD prevalence within this population was 49.8% which is significantly higher than the global pooled prevalence of 25%. This highlights the importance of robust, prospective studies like this to enable collection of longitudinal data on risk factors, disease progression and to facilitate future interventional studies. Future plans The complete analysis of data collected from this cohort will give valuable insights into the interaction of the phenotypic and genotypic profiles that result in such a dramatic increased risk of NAFLD within the Indian population. The cohort will also form the basis of future lifestyle interventional studies, aimed at improving liver and metabolic health
Scaling of the B and D meson spectrum in lattice QCD
We give results for the and the meson spectrum using NRQCD on the
lattice in the quenched approximation. The masses of radially and orbitally
excited states are calculated as well as -wave hyperfine and -wave fine
structure. Radially excited -states are observed for the first time. Radial
and orbital excitation energies match well to experiment, as does the
strange-non-strange -wave splitting. We compare the light and heavy quark
mass dependence of various splittings to experiment. Our -results cover a
range in lattice spacings of more than a factor of two. Our -results are
from a single lattice spacing and we compare them to numbers in the literature
from finer lattices using other methods. We see no significant dependence of
physical results on the lattice spacing.
PACS: 11.15.Ha 12.38.Gc 14.40.Lb 14.40.NdComment: 78 pages, 29 tables, 30 figures Revised version. Minor corrections to
spelling and wordin
Kaon B Parameter in Quenched QCD
I calculate the kaon B-parameter with a lattice simulation in quenched
approximation. The lattice simulation uses an action possessing exact lattice
chiral symmetry, an overlap action. Computations are performed at two lattice
spacings, about 0.13 and 0.09 fm (parameterized by Wilson gauge action
couplings beta=5.9 and 6.1) with nearly the same physical volumes and quark
masses. I describe particular potential difficulties which arise due to the use
of such a lattice action in finite volume. My results are consistent with other
recent lattice determinations using domain-wall fermions.Comment: 23 pages, Revtex, 16 postscript figure
Comparative Study of full QCD Hadron Spectrum and Static Quark Potential with Improved Actions
We investigate effects of action improvement on the light hadron spectrum and
the static quark potential in two-flavor QCD for GeV and
. We compare a renormalization group improved action with
the plaquette action for gluons, and the SW-clover action with the Wilson
action for quarks. We find a significant improvement in the hadron spectrum by
improving the quark action, while the gluon improvement is crucial for a
rotationally invariant static potential. We also explore the region of light
quark masses corresponding to on a 2.7 fm lattice using
the improved gauge and quark action. A flattening of the potential is not
observed up to 2 fm.Comment: LaTeX, 35 pages, 22 eps figures, uses revtex and eps
The , interaction in finite volume and the resonance
In this work the interaction of the coupled channels and
in an SU(4) extrapolation of the chiral unitary theory, where the
resonance appears as dynamically generated from that
interaction, is extended to produce results in finite volume. Energy levels in
the finite box are evaluated and, assuming that they would correspond to
lattice results, the inverse problem of determining the phase shifts in the
infinite volume from the lattice results is solved. We observe that it is
possible to obtain accurate phase shifts and the position of the
resonance, but it requires the explicit consideration of the
two coupled channels. We also observe that some of the energy levels in the box
are attached to the closed channel, such that their use to induce the phase shifts via L\"uscher's formula leads to incorrect results.Comment: 10 pages, 13 figures, accepted for publication in Eur. Phys. J.
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