210 research outputs found
Preconditioning Maximal Center Gauge with Stout Link Smearing in SU(3)
Center vortices are studied in SU(3) gauge theory using Maximal Center Gauge
(MCG) fixing. Stout link smearing and over-improved stout link smearing are
used to construct a preconditioning gauge field transformation, applied to the
original gauge field before fixing to MCG. We find that preconditioning
successfully achieves higher gauge fixing maxima. We observe a reduction in the
number of identified vortices when preconditioning is used, and also a
reduction in the vortex-only string tension.Comment: 9 pages, 4 figure
Prüfung der Saatgutherkunft aus ökologischem und konventionellem Anbau bei Wintergetreide
The impact of seed source (conventional or organic farming) is one important question for the variety trials under the conditions of organic farming. Hence, field trials were
conducted at two sites in Bavaria in two years (2013-2014). Certified organic seed from a Bavarian propagation were compared to conventional seed, offered by breeders for national variety trials. One until two varieties were examined for winter rye and for winter triticale in each year. Organic seed often showed higher crude protein content, conventional seed had mainly higher thousand seed weight and often superior germination power.
The grain yield was mostly higher for conventionally produced seeds than for organic seed at one site, whereas seed source showed no differences with one exception at
the other site. A high positive correlation was determined for yield and above all germination power for rye. But all in all, data basis is too low for general conclusion.
Future research should focus on more varieties and different soil and climate condition. Seed should be difference concerning cultivation only in the last year in future investigation
Role of center vortices in chiral symmetry breaking in SU(3) gauge theory
We study the behavior of the AsqTad quark propagator in Landau gauge on SU(3)
Yang-Mills gauge configurations under the removal of center vortices. In SU(2)
gauge theory, center vortices have been observed to generate chiral symmetry
breaking and dominate the infrared behavior of the quark propagator. In
contrast, we report a weak dependence on the vortex content of the gauge
configurations, including the survival of dynamical mass generation on
configurations with vanishing string tension.Comment: 8 pages, 9 figure
Charmonium spectral functions in Nf=2 QCD
We report on a study of charmonium at high temperature in 2-flavour QCD. This
is the first such study with dynamical fermions. Using an improved anisotropic
lattice action, spectral functions are extracted from correlators in the vector
and pseudoscalar channels. No signs of medium-induced suppression of the ground
states are seen for temperatures up to 1.5T_c, while at T~2T_c there are clear
signs of modifications. The current systematic and statistical uncertainties in
our data, in particular the relatively coarse lattice and small volume, do not
allow us to draw a firm conclusion at this stage.Comment: 6 pages, talk by JIS at Lattice 2005 (Non-zero temperature and
density
The spectrum of radial, orbital and gluonic excitations of charmonium
We present results for the charmonium spectrum from dynamical QCD
simulations on anisotropic lattices. Using all-to-all
propagators we determine the ground and excited states of S, P and D waves and
hybrids. We also evaluate the disconnected (OZI suppressed) contribution to the
and Comment: 6 pages, 3 figures, Presented at 24th International Symposium on
Lattice Field Theory (Lattice 2006), Tucson, Arizona, 23-28 Jul 200
SU(3) centre vortices underpin confinement and dynamical chiral symmetry breaking
The mass function of the nonperturbative quark propagator in SU(3) gauge
theory shows only a weak dependence on the vortex content of the gauge
configurations. Of particular note is the survival of dynamical mass generation
on vortex-free configurations having a vanishing string tension. This admits
the possibility that mass generation associated with dynamical chiral symmetry
breaking persists without confinement. In this presentation, we examine the
low-lying ground-state hadron spectrum of the pi, rho, N and Delta and discover
that while dynamical mass generation persists in the vortex-free theory, it is
not connected to dynamical chiral symmetry breaking. In this way, centre
vortices in SU(3) gauge theory are intimately linked to both confinement and
dynamical chiral symmetry breaking. We conclude that centre vortices are the
essential underlying feature of the QCD vacuum.Comment: 7 pages, 8 figues. Manuscript accepted for Publication in Phys. Rev.
Ortho-to-para ratio of interstellar heavy water
Despite the low elemental deuterium abundance in the Galaxy, enhanced
molecular D/H ratios have been found in the environments of low-mass star
forming regions, and in particular the Class 0 protostar IRAS 16293-2422. The
CHESS (Chemical HErschel Surveys of Star forming regions) Key Program aims at
studying the molecular complexity of the interstellar medium. The high
sensitivity and spectral resolution of the HIFI instrument provide a unique
opportunity to observe the fundamental 1,1,1 - 0,0,0 transition of the
ortho-D2O molecule, inaccessible from the ground, and to determine the
ortho-to-para D2O ratio. We have detected the fundamental transition of the
ortho-D2O molecule at 607.35 GHz towards IRAS 16293-2422. The line is seen in
absorption with a line opacity of 0.62 +/- 0.11 (1 sigma). From the previous
ground-based observations of the fundamental 1,1,0 - 1,0,1 transition of
para-D2O seen in absorption at 316.80 GHz we estimate a line opacity of 0.26
+/- 0.05 (1 sigma). We show that the observed absorption is caused by the cold
gas in the envelope of the protostar. Using these new observations, we estimate
for the first time the ortho to para D2O ratio to be lower than 2.6 at a 3
sigma level of uncertainty, to be compared with the thermal equilibrium value
of 2:1.Comment: 5 pages, 5 figures, accepted the A&A HIFI Special Issue as a lette
Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)
The HIFI instrument on board the Herschel Space Observatory has been used to
observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4
in order to improve our understanding of the interstellar chemistry of
nitrogen. We report observations of absorption in NH N=1-0, J=2-1 and ortho-NH2
1_1,1-0_0,0. We also observed ortho-NH3 1_0-0_0, and 2_0-1_0, para-NH3 2_1-1_1,
and searched unsuccessfully for NH+. All detections show emission and
absorption associated directly with the hot-core source itself as well as
absorption by foreground material over a wide range of velocities. All spectra
show similar, non-saturated, absorption features, which we attribute to diffuse
molecular gas. Total column densities over the velocity range 11-54 km/s are
estimated. The similar profiles suggest fairly uniform abundances relative to
hydrogen, approximately 6*10^-9, 3*10^-9, and 3*10^-9 for NH, NH2, and NH3,
respectively. These abundances are discussed with reference to models of
gas-phase and surface chemistry.Comment: 5 pages, 3 figures, 2 online pages with 2 figures. Accepted for
publication in A&A July 6 (Herschel/HIFI special issue
Strong absorption by interstellar hydrogen fluoride: Herschel/HIFI observations of the sight-line to G10.6-0.4 (W31C)
We report the detection of strong absorption by interstellar hydrogen
fluoride along the sight-line to the submillimeter continuum source G10.6-0.4
(W31C). We have used Herschel's HIFI instrument, in dual beam switch mode, to
observe the 1232.4763 GHz J=1-0 HF transition in the upper sideband of the Band
5a receiver. The resultant spectrum shows weak HF emission from G10.6-0.4 at
LSR velocities in the range -10 to -3 km/s, accompanied by strong absorption by
foreground material at LSR velocities in the range 15 to 50 km/s. The spectrum
is similar to that of the 1113.3430 GHz 1(11)-0(00) transition of para-water,
although at some frequencies the HF (hydrogen fluoride) optical depth clearly
exceeds that of para-H2O. The optically-thick HF absorption that we have
observed places a conservative lower limit of 1.6E+14 cm-2 on the HF column
density along the sight-line to G10.6-0.4. Our lower limit on the HF abundance,
6E-9 relative to hydrogen nuclei, implies that hydrogen fluoride accounts for
between ~ 30 and 100% of the fluorine nuclei in the gas phase along this
sight-line. This observation corroborates theoretical predictions that -
because the unique thermochemistry of fluorine permits the exothermic reaction
of F atoms with molecular hydrogen - HF will be the dominant reservoir of
interstellar fluorine under a wide range of conditions.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue). This revised version corrects a typographic error in the HTML
abstract, in which the lower limit on the HF abundance (should be 6E-9) was
previously misstated. The abstract in the PDF version is correct and the
latter has not been modifie
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