518 research outputs found
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
Moral wrongs, disadvantages, and disability: a critique of critical disability studies
Critical disability studies (CDS) has emerged as an approach to the study of disability over the last decade or so and has sought to present a challenge to the predominantly materialist line found in the more conventional disability studies approaches. In much the same way that the original development of the social model resulted in a necessary correction to the overly individualized accounts of disability that prevailed in much of the interpretive accounts which then dominated medical sociology, so too has CDS challenged the materialist line of disability studies. In this paper we review the ideas behind this development and analyse and critique some of its key ideas. The paper starts with a brief overview of the main theorists and approaches contained within CDS and then moves on to normative issues; namely, to the ethical and political applicability of CDS
Study of Charmonia near the deconfining transition on an anisotropic lattice with O(a) improved quark action
We study hadron properties near the deconfining transition in the quenched
lattice QCD simulation. This paper focuses on the heavy quarkonium states, such
as meson. In order to treat heavy quarks at , we adopt the
improved Wilson action on anisotropic lattice. We discuss bound
state observing the wave function and compare the meson correlators at above
and below . Although we find a large change of correlator near the ,
the strong spatial correlation which is almost the same as confinement phase
survives even .Comment: 19 pages, 10 figure
Tadpole-improved SU(2) lattice gauge theory
A comprehensive analysis of tadpole-improved SU(2) lattice gauge theory is
made. Simulations are done on isotropic and anisotropic lattices, with and
without improvement. Two tadpole renormalization schemes are employed, one
using average plaquettes, the other using mean links in Landau gauge.
Simulations are done with spatial lattice spacings in the range of about
0.1--0.4 fm. Results are presented for the static quark potential, the
renormalized lattice anisotropy (where is the ``temporal''
lattice spacing), and for the scalar and tensor glueball masses. Tadpole
improvement significantly reduces discretization errors in the static quark
potential and in the scalar glueball mass, and results in very little
renormalization of the bare anisotropy that is input to the action. We also
find that tadpole improvement using mean links in Landau gauge results in
smaller discretization errors in the scalar glueball mass (as well as in the
static quark potential), compared to when average plaquettes are used. The
possibility is also raised that further improvement in the scalar glueball mass
may result when the coefficients of the operators which correct for
discretization errors in the action are computed beyond tree level.Comment: 14 pages, 7 figures (minor changes to overall scales in Fig.1; typos
removed from Eqs. (3),(4),(15); some rewording of Introduction
S and P-wave heavy-light mesons in lattice NRQCD
The mass spectrum of S and P-wave mesons containing a single heavy quark is
computed in the quenched approximation, using NRQCD up to third order in the
inverse heavy quark mass expansion. Previous results found third order
contributions which are as large in magnitude as the total second order
contribution for the charmed S-wave spin splitting. The present work considers
variations such as anisotropic lattices, Landau link tadpole improvement, and a
highly-improved light quark action, and finds that the second order correction
to the charmed S-wave spin splitting is about 20% of the leading order
contribution, while the third order correction is about 20%(10%) for
D^*-D(D_s^*-D_s). Nonleading corrections are very small for the bottom meson
spectrum, and are statistically insignificant for the P-wave charmed masses.
The relative orderings among P-wave charmed and bottom mesons, and the sizes of
the mass splittings, are discussed in light of experimental data and existing
calculations.Comment: 21 pages including 6 figures, changed method of fitting correlators,
this version to be published in Phys Rev
The glueball spectrum from an anisotropic lattice study
The spectrum of glueballs below 4 GeV in the SU(3) pure-gauge theory is
investigated using Monte Carlo simulations of gluons on several anisotropic
lattices with spatial grid separations ranging from 0.1 to 0.4 fm. Systematic
errors from discretization and finite volume are studied, and the continuum
spin quantum numbers are identified. Care is taken to distinguish single
glueball states from two-glueball and torelon-pair states. Our determination of
the spectrum significantly improves upon previous Wilson action calculations.Comment: 14 pages, 8 figures, uses REVTeX and epsf.sty (final version
published in Physical Review D
Measuring the aspect ratio renormalization of anisotropic-lattice gluons
Using tadpole inproved actions we investigate the consistency between
different methods of measuring the aspect ratio renormalization of
anisotropic-lattice gluons for bare aspect ratios \chi_0=4,6,10 and inverse
lattice spacing in the range a_s^{-1}=660-840 MeV. The tadpole corrections to
the action, which are established self-consistently, are defined for two cases,
mean link tadpoles in Landau gauge and gauge invariant mean plaquette tadpoles.
Parameters in the latter case exhibited no dependence on the spatial lattice
size, L, while in the former, parameters showed only a weak dependence on L
easily extrapolated to L=\infty.
The renormalized anisotropy \chi_R was measured using both the torelon
dispersion relation and the sideways potential method. We found good agreement
between these different approaches. Any discrepancy was at worst 3-4% which is
consistent with the effect of lattice artifacts that for the torelon we
estimate as O(\a_Sa_s^2/R^2) where R is the flux-tube radius.
We also present some new data that suggests that rotational invariance is
established more accurately for the mean-link action than the plaquette action.Comment: LaTeX 18 pages including 7 figure
Tadpole renormalization and relativistic corrections in lattice NRQCD
We make a comparison of two tadpole renormalization schemes in the context of
the quarkonium hyperfine splittings in lattice NRQCD. Improved gauge-field and
NRQCD actions are analyzed using the mean-link in Landau gauge, and
using the fourth root of the average plaquette . Simulations are done
for , , and systems. The hyperfine splittings are
computed both at leading and at next-to-leading order in the relativistic
expansion. Results are obtained at lattice spacings in the range of about
0.14~fm to 0.38~fm. A number of features emerge, all of which favor tadpole
renormalization using . This includes much better scaling behavior of
the hyperfine splittings in the three quarkonium systems when is
used. We also find that relativistic corrections to the spin splittings are
smaller when is used, particularly for the and
systems. We also see signs of a breakdown in the NRQCD expansion when the bare
quark mass falls below about one in lattice units. Simulations with
also appear to be better behaved in this context: the bare quark masses turn
out to be larger when is used, compared to when is used on
lattices with comparable spacings. These results also demonstrate the need to
go beyond tree-level tadpole improvement for precision simulations.Comment: 14 pages, 7 figures (minor changes to some phraseology and
references
Theorising Disability: Beyond Common Sense
This article seeks to introduce the topic of disability to political theory via a discussion of some of the literature produced by disability theorists. The author argues that these more radical approaches conceptualise disability in ways that conflict with âcommon-senseâ notions of disability that tend to underpin political theoretical considerations of the topic. Furthermore, the author suggests that these more radical conceptualisations have profound implications for current debates on social justice, equality and citizenship that highlight the extent to which these notions are also currently underpinned by âcommon-senseâ notions of ânormalityâ
Mesonic decay constants in lattice NRQCD
Lattice NRQCD with leading finite lattice spacing errors removed is used to
calculate decay constants of mesons made up of heavy quarks. Quenched
simulations are done with a tadpole improved gauge action containing plaquette
and six-link rectangular terms. The tadpole factor is estimated using the
Landau link. For each of the three values of the coupling constant considered,
quarkonia are calculated for five masses spanning the range from charmonium
through bottomonium, and one set of quark masses is tuned to the B(c).
"Perturbative" and nonperturbative meson masses are compared. One-loop
perturbative matching of lattice NRQCD with continuum QCD for the heavy-heavy
vector and axial vector currents is performed. The data are consistent with the
vector meson decay constants of quarkonia being proportional to the square root
of their mass and the B(c) decay constant being equal to 420(13) MeV.Comment: 25 pages in REVTe
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