2,062 research outputs found
Alien Registration- Laine, Kusta V. (Greenwood, Oxford County)
https://digitalmaine.com/alien_docs/15677/thumbnail.jp
The leading non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure
Using Numerical Stochastic Perturbation Theory within three-dimensional pure
SU(3) gauge theory, we estimate the last unknown renormalization constant that
is needed for converting the vacuum energy density of this model from lattice
regularization to the MSbar scheme. Making use of a previous non-perturbative
lattice measurement of the plaquette expectation value in three dimensions,
this allows us to approximate the first non-perturbative coefficient that
appears in the weak-coupling expansion of hot QCD pressure.Comment: 16 pages. v2: published versio
Renormalization of infrared contributions to the QCD pressure
Thanks to dimensional reduction, the infrared contributions to the QCD
pressure can be obtained from two different three-dimensional effective field
theories, called the Electrostatic QCD (Yang-Mills plus adjoint Higgs) and the
Magnetostatic QCD (pure Yang-Mills theory). Lattice measurements have been
carried out within these theories, but a proper interpretation of the results
requires renormalization, and in some cases also improvement, i.e. the removal
of terms of O(a) or O(a^2). We discuss how these computations can be
implemented and carried out up to 4-loop level with the help of Numerical
Stochastic Perturbation Theory.Comment: 7 pages, 4 figures, talk presented at Lattice 2006 (High temperature
and density
Quark mass thresholds in QCD thermodynamics
We discuss radiative corrections to how quark mass thresholds are crossed, as
a function of the temperature, in basic thermodynamic observables such as the
pressure, the energy and entropy densities, and the heat capacity of high
temperature QCD. The indication from leading order that the charm quark plays a
visible role at surprisingly low temperatures, is confirmed. We also sketch a
way to obtain phenomenological estimates relevant for generic expansion rate
computations at temperatures between the QCD and electroweak scales, pointing
out where improvements over the current knowledge are particularly welcome.Comment: 14 pages. v2: minor additions and clarifications; published versio
Meson Correlation Function and Screening Mass in Thermal QCD
Analytical results for the spatial dependence of the correlation functions
for all meson excitations in perturbative Quantum Chromodynamics, the lowest
order, are calculated. The meson screening mass is obtained as a large distance
limit of the correlation function. Our analysis leads to a better understanding
of the excitations of Quark Gluon Plasma at sufficiently large temperatures and
may be of relevance for future numerical calculations with fully interacting
Quantum Chromodynamics.Comment: 11 page
A remark on sphaleron erasure of baryon asymmetry
We complete an existing result for how the baryon asymmetry left over after a
period of full thermal equilibrium depends on different lepton asymmetries.Comment: 5 pages; small clarifications and a reference added; to appear in PR
Giant HII Regions in NGC 7479 & NGC 6070
We present new results from our search for Giant H\,{\sc ii} Regions in
galaxies visible from the southern hemisphere. In this work we study two
galaxies: NGC\,7479 and NGC\,6070. Using high-resolution spectra, obtained with
different instruments at Las Campanas Observatory, we are able to resolve the
emission-line profile widths and determine the intrinsic velocity dispersion of
the ionised gas. We detect profile widths corresponding to supersonic velocity
dispersions in the six observed H\,{\sc ii} regions. We find that all of them
show at least two distinct kinematical components: a relatively narrow feature
(between ~11 and ~22\kms) and a broader (between ~31 and ~77\kms) component.
Two of the regions show a complex narrow profile in all ion lines, which can be
further split into two components with different radial velocities. Whereas the
wing broadening of the overall profile can be fitted with a low-intensity broad
component for almost all profiles, in one region it was better reproduced by
two separate shell-like wings. We have analysed the impact that the presence of
multiple components has on the location of the H{\sc ii} regions in the
plane. Although the overall distribution confirms the
presence of a regression, the precise location of the regions in the plane is
strongly dependent on the components derived from the profile fitting.Comment: This manuscript has been accepted for publication in Monthly Notices
of the Royal Astronomical Society Main Journal. 16 pages, 11 figure
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