70 research outputs found
Divergent IR gluon propagator from Ward-Slavnov-Taylor identities?
We exploit the Ward-Slavnov-Taylor identity relating the 3-gluons to the
ghost-gluon vertices to conclude either that the ghost dressing function is
finite and non vanishing at zero momentum while the gluon propagator diverges
(although it may do so weakly enough not to be in contradiction with current
lattice data) or that the 3-gluons vertex is non-regular when one momentum goes
to zero. We stress that those results should be kept in mind when one studies
the Infrared properties of the ghost and gluon propagators, for example by
means of Dyson-Schwinger equations.Comment: 6 pages, bibte
Instanton dominance over at low momenta from lattice QCD simulations at , and
We report on an instanton-based analysis of the gluon Green functions in the
Landau gauge for low momenta; in particular we use lattice results for
in the symmetric momentum subtraction scheme () for
large-volume lattice simulations. We have exploited quenched gauge field
configurations, , with both Wilson and tree-level Symanzik improved
actions, and unquenched ones with and dynamical flavors
(domain wall and twisted-mass fermions, respectively).
We show that the dominance of instanton correlations on the low-momenta gluon
Green functions can be applied to the determination of phenomenological
parameters of the instanton liquid and, eventually, to a determination of the
lattice spacing.
We furthermore apply the Gradient Flow to remove short-distance fluctuations.
The Gradient Flow gets rid of the QCD scale, , and reveals
that the instanton prediction extents to large momenta. For those gauge field
configurations free of quantum fluctuations, the direct study of topological
charge density shows the appearance of large-scale lumps that can be identified
as instantons, giving access to a direct study of the instanton density and
size distribution that is compatible with those extracted from the analysis of
the Green functions.Comment: Proceedings of the 35th International Symposium on Lattice Field
Theory, Granada, Spai
Non-perturbative Power Corrections to Ghost and Gluon Propagators
We study the dominant non-perturbative power corrections to the ghost and
gluon propagators in Landau gauge pure Yang-Mills theory using OPE and lattice
simulations. The leading order Wilson coefficients are proven to be the same
for both propagators. The ratio of the ghost and gluon propagators is thus free
from this dominant power correction. Indeed, a purely perturbative fit of this
ratio gives smaller value (MeV) of \Lambda_{\ms} than the one
obtained from the propagators separately(MeV). This argues in
favour of significant non-perturbative power corrections in the
ghost and gluon propagators. We check the self-consistency of the method.Comment: 14 pages, 4 figures; replaced with revised version, to appear in JHE
The strong coupling constant at small momentum as an instanton detector
We present a study of at small p computed from the lattice.
It shows a dramatic law which can be understood within an
instanton liquid model. In this framework the prefactor gives a direct measure
of the instanton density in thermalised configurations. A preliminary result
for this density is 5.27(4) fm^{-4}.Comment: 12 pages, 4 figure
Testing OPE for ghosts, gluons and
We present here our results on extracting Wilson coefficients from different
quantities such as ghost and gluon propagators which are calculated by means of
Lattice QCD. The results confirm the validity of our method for the calculation
of the strong coupling constant as well as allow to estimate the range of
momenta where OPE is applicable.Comment: arXiv admin note: substantial text overlap with arXiv:1301.759
High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots
We compare the quality factor values of the whispery gallery modes of
microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers
by performing room temperature photoluminescence (PL) spectroscopy. The PL
measurements show a large number of high Q factor (Q) resonant modes on the
whole spectrum which allows us to identify the different radial mode families
and to compare them with simulations. We report a considerable improvement of
the Q factor which reflect the etching quality and the relatively low cavity
loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very
high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks
embedding QDs grown on AlGaN barrier layer. We attribute this difference to the
lower absorption below bandgap for AlN barrier layers at the energies of our
experimental investigation
k.p theory beyond standard 8-band theory parametrization strategies and its applicability in electronic and optoelectronic devices design
International audienc
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