17,725 research outputs found
Corrections to the Gell-Mann-Oakes-Renner relation and chiral couplings and
Next to leading order corrections to the
Gell-Mann-Oakes-Renner relation (GMOR) are obtained using weighted QCD Finite
Energy Sum Rules (FESR) involving the pseudoscalar current correlator. Two
types of integration kernels in the FESR are used to suppress the contribution
of the kaon radial excitations to the hadronic spectral function, one with
local and the other with global constraints. The result for the pseudoscalar
current correlator at zero momentum is , leading to the chiral corrections to GMOR: . The resulting uncertainties are mostly due to variations in the upper
limit of integration in the FESR, within the stability regions, and to a much
lesser extent due to the uncertainties in the strong coupling and the strange
quark mass. Higher order quark mass corrections, vacuum condensates, and the
hadronic resonance sector play a negligible role in this determination. These
results confirm an independent determination from chiral perturbation theory
giving also very large corrections, i.e. roughly an order of magnitude larger
than the corresponding corrections in chiral . Combining
these results with our previous determination of the corrections to GMOR in
chiral , , we are able to determine two low
energy constants of chiral perturbation theory, i.e. , and , both at the
scale of the -meson mass.Comment: Revised version with minor correction
Shock waves in capillary collapse of colloids: a model system for two--dimensional screened Newtonian gravity
Using Brownian dynamics simulations, density functional theory, and
analytical perturbation theory we study the collapse of a patch of
interfacially trapped, micrometer-sized colloidal particles, driven by
long-ranged capillary attraction. This attraction {is formally analogous} to
two--dimensional (2D) screened Newtonian gravity with the capillary length
\hat{\lambda} as the screening length. Whereas the limit \hat{\lambda} \to
\infty corresponds to the global collapse of a self--gravitating fluid, for
finite \hat{\lambda} we predict theoretically and observe in simulations a
ringlike density peak at the outer rim of a disclike patch, moving as an
inbound shock wave. Possible experimental realizations are discussed.Comment: 5 pages, 3 figures, revised version with new Refs. added, matches
version accepted for publication in PR
Influence of the Feedback Filter on the Response of the Pulsed Digital Oscillator
This paper introduces a new feedback topology for the Pulsed Digital
Oscillator (PDO) and compares it to the classical topology. The `classic' or
single feedback topology, introduced in previous works, shows a strong behavior
dependence on the damping losses in the MEMS resonator. A new double feedback
topology is introduced here in order to help solving this problem. Comparative
discrete-time simulations and preliminary experimental measurements have been
carried out for both topologies, showing how the new double feedback topology
may increase PDO performance for some frequency ranges.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Chiral corrections to the Gell-Mann-Oakes-Renner relation
The next to leading order chiral corrections to the
Gell-Mann-Oakes-Renner (GMOR) relation are obtained using the pseudoscalar
correlator to five-loop order in perturbative QCD, together with new finite
energy sum rules (FESR) incorporating polynomial, Legendre type, integration
kernels. The purpose of these kernels is to suppress hadronic contributions in
the region where they are least known. This reduces considerably the systematic
uncertainties arising from the lack of direct experimental information on the
hadronic resonance spectral function. Three different methods are used to
compute the FESR contour integral in the complex energy (squared) s-plane, i.e.
Fixed Order Perturbation Theory, Contour Improved Perturbation Theory, and a
fixed renormalization scale scheme. We obtain for the corrections to the GMOR
relation, , the value . This result
is substantially more accurate than previous determinations based on QCD sum
rules; it is also more reliable as it is basically free of systematic
uncertainties. It implies a light quark condensate . As a byproduct, the chiral perturbation theory (unphysical) low energy
constant is predicted to be , or .Comment: A comment about the value of the strong coupling has been added at
the end of Section 4. No change in results or conslusion
Gas expulsion in highly substructured embedded star clusters
We investigate the response of initially substructured, young, embedded star
clusters to instantaneous gas expulsion of their natal gas. We introduce
primordial substructure to the stars and the gas by simplistically modelling
the star formation process so as to obtain a variety of substructure
distributed within our modelled star forming regions. We show that, by
measuring the virial ratio of the stars alone (disregarding the gas
completely), we can estimate how much mass a star cluster will retain after gas
expulsion to within 10% accuracy, no matter how complex the background
structure of the gas is, and we present a simple analytical recipe describing
this behaviour. We show that the evolution of the star cluster while still
embedded in the natal gas, and the behavior of the gas before being expelled,
are crucial processes that affect the timescale on which the cluster can evolve
into a virialized spherical system. Embedded star clusters that have high
levels of substructure are subvirial for longer times, enabling them to survive
gas expulsion better than a virialized and spherical system. By using a more
realistic treatment for the background gas than our previous studies, we find
it very difficult to destroy the young clusters with instantaneous gas
expulsion. We conclude that gas removal may not be the main culprit for the
dissolution of young star clusters.Comment: 19 pages, 8 figures, 2 tables. Accepted for publication in MNRA
SPH simulations of the chemical evolution of bulges
We have implemented a chemical evolution model on the parallel AP3M+SPH DEVA
code which we use to perform high resolution simulations of spiral galaxy
formation. It includes feedback by SNII and SNIa using the Qij matrix
formalism. We also include a diffusion mechanism that spreads newly introduced
metals. The gas cooling rate depends on its specific composition. We study the
stellar populations of the resulting bulges finding a potential scenario where
they seem to be composed of two populations: an old, metal poor,
-enriched population, formed in a multiclump scenario at the beginning
of the simulation and a younger one, formed by slow accretion of satellites or
gas, possibly from the disk due to instabilities.Comment: 2 pages, 3 figures. Proceedings of IAUS 245 "Formation and Evolution
of Galaxy Bulges
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