968 research outputs found
New issues for Numerical Stochastic Perturbation Theory
First attempts in the application of Numerical Stochastic Perturbation Theory
(NSPT) to the problem of pushing one loop further the computation of SU(3)
(SU(2)) pertubative beta function (in different schemes) are reviewed and the
relevance of such a computation is discussed. Other issues include the proposal
of a different strategy for gauge-fixed NSPT computations in lattice QCD.Comment: 3 pages, Latex, LATTICE98(algorithms
The gradient flow running coupling with twisted boundary conditions
We study the gradient flow for Yang-Mills theories with twisted boundary
conditions. The perturbative behavior of the energy density is used to define a running coupling at a scale given by the
linear size of the finite volume box. We compute the non-perturbative running
of the pure gauge coupling constant and conclude that the technique is
well suited for further applications due to the relatively mild cutoff effects
of the step scaling function and the high numerical precision that can be
achieved in lattice simulations. We also comment on the inclusion of matter
fields.Comment: 27 pages. LaTe
Meson Spectral Functions at finite Temperature
The Maximum Entropy Method provides a Bayesian approach to reconstruct the
spectral functions from discrete points in Euclidean time. The applicability of
the approach at finite temperature is probed with the thermal meson correlation
function. Furthermore the influence of fuzzing/smearing techniques on the
spectral shape is investigated. We present first results for meson spectral
functions at several temperatures below and above . The correlation
functions were obtained from quenched calculations with Clover fermions on
large isotropic lattices of the size . We compare the
resulting pole masses with the ones obtained from standard 2-exponential fits
of spatial and temporal correlation functions at finite temperature and in the
vacuum. The deviation of the meson spectral functions from free spectral
functions is examined above the critical temperature.Comment: Lattice2001(hightemp), 3 pages, 6 figure
Does the XY Model have an integrable continuum limit?
The quantum field theory describing the massive O(2) nonlinear sigma-model is
investigated through two non-perturbative constructions: The form factor
bootstrap based on integrability and the lattice formulation as the XY model.
The S-matrix, the spin and current two-point functions, as well as the 4-point
coupling are computed and critically compared in both constructions. On the
bootstrap side a new parafermionic super selection sector is found; in the
lattice theory a recent prediction for the (logarithmic) decay of lattice
artifacts is probed.Comment: 69 pages, 18 figures. Equation (3.20) correcte
Three-Dimensional SU(3) gauge theory and the Spatial String Tension of the (3+1)-Dimensional Finite Temperature SU(3) Gauge Theory
We establish a close relation between the spatial string tension of the
(3+1)-dimensional gauge theory at finite temperature () and
the string tension of the 3-dimensional gauge theory () which
is similar to what has been found previously for . We obtain
and , respectively. For temperatures larger than twice the critical
temperature results are consistent with a temperature dependent coupling
running according to the two-loop -function with .Comment: 11 pages (4 figures
Assessment of atherosclerosis: the role of flow-mediated dilatation
Evidence suggests that endothelial dysfunction is on the causal pathway for both atherogenesis and destabilization of established plaques. In this review, the role of flow-mediated dilatation (FMD) as a non-invasive method to assess endothelial function is discussed. Technical modifications and development of analysis software have significantly improved the variability of the method. Following a strict standardized protocol enables reproducible measurements to be achieved and export of the technique from specialized laboratories to population studies and multicentre settings. Endothelial function assessed by FMD has been shown to be affected by cardiovascular risk factors, to be related to structural arterial disease and to cardiovascular outcome, validating its use for studying the pathophysiology of arterial disease. Numerous studies have also demonstrated that it is responsive to physiological and pharmacological interventions. Flow-mediated dilatation provides unique opportunities in drug development programmes to assess an early rapidly responsive signal of risk or benefit, complementing endpoints of structural arterial disease and cardiovascular outcomes that take much longer and are more expensiv
Umbilical endometriosis
We report two women who presented with a recurrent, mildly painful, bluish nodule in the umbilicus. Both patients complained of local tenderness and occasional bleeding that increased during menstruation. Neither patient had had previous pelvic surgery. Excision of the lesions revealed a primary umbilical endometriosis; in one case, a simultaneous laparoscopy showed a pelvic endometriosis. We review the current literature and discuss the possible etiopathogenesis and when a laparoscopy is indicated to diagnose a concomitant pelvic endometriosis. Umbilical endometriosis is a very rare disease but should be considered in the differential diagnosis of umbilical lesion
Determining the conformal window: SU(2) gauge theory with N_f = 4, 6 and 10 fermion flavours
We study the evolution of the coupling in SU(2) gauge field theory with
, 6 and 10 fundamental fermion flavours on the lattice. These values are
chosen close to the expected edges of the conformal window, where the theory
possesses an infrared fixed point. We use improved Wilson-clover action, and
measure the coupling in the Schr\"odinger functional scheme. At four flavours
we observe that the couping grows towards the infrared, implying QCD-like
behaviour, whereas at ten flavours the results are compatible with a Banks-Zaks
type infrared fixed point. The six flavour case remains inconclusive: the
evolution of the coupling is seen to become slower at the infrared, but the
accuracy of the results falls short from fully resolving the fate of the
coupling. We also measure the mass anomalous dimension for the case.Comment: 22 pages, 12 figures. Proof readin
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