1,690 research outputs found
Chiral Extrapolation of Lattice Data for Heavy Meson Hyperfine Splittings
We investigate the chiral extrapolation of the lattice data for the
light-heavy meson hyperfine splittings D^*-D and B^*-B to the physical region
for the light quark mass. The chiral loop corrections providing non-analytic
behavior in m_\pi are consistent with chiral perturbation theory for heavy
mesons. Since chiral loop corrections tend to decrease the already too low
splittings obtained from linear extrapolation, we investigate two models to
guide the form of the analytic background behavior: the constituent quark
potential model, and the covariant model of QCD based on the ladder-rainbow
truncation of the Dyson-Schwinger equations. The extrapolated hyperfine
splittings remain clearly below the experimental values even allowing for the
model dependence in the description of the analytic background.Comment: 14 pages, 4 figures, typos corrected, presentation clarifie
K_{l3} transition form factors
The rainbow truncation of the quark Dyson-Schwinger equation is combined with
the ladder Bethe-Salpeter equation for the meson bound state amplitudes and the
dressed quark-W vertex in a manifestly covariant calculation of the K_{l3}
transition form factors and decay width in impulse approximation. With model
gluon parameters previously fixed by the chiral condensate, the pion mass and
decay constant, and the kaon mass, our results for the K_{l3} form factors and
the kaon semileptonic decay width are in good agreement with the experimental
data.Comment: 8 pages, 3 figures, Revte
Pseudoscalar and vector mesons as q\bar{q} bound states
Two-body bound states such as mesons are described by solutions of the
Bethe-Salpeter equation. We discuss recent results for the pseudoscalar and
vector meson masses and leptonic decay constants, ranging from pions up to
c\bar{c} bound states. Our results are in good agreement with data. Essential
in these calculation is a momentum-dependent quark mass function, which evolves
from a constituent-quark mass in the infrared region to a current-quark mass in
the perturbative region. In addition to the mass spectrum, we review the
electromagnetic form factors of the light mesons. Electromagnetic current
conservation is manifest and the influence of intermediate vector mesons is
incorporated self-consistently. The results for the pion form factor are in
excellent agreement with experiment.Comment: 8 pages, 6 .eps figures, contribution to the proceedings of the first
meeting of the APS Topical Group on Hadron Physics, Fermilab, Oct. 200
Aspects and consequences of a dressed-quark-gluon vertex
Features of the dressed-quark-gluon vertex and their role in the gap and
Bethe-Salpeter equations are explored. It is argued that quenched lattice data
indicate the existence of net attraction in the colour-octet projection of the
quark-antiquark scattering kernel. This attraction affects the uniformity with
which solutions of truncated equations converge pointwise to solutions of the
complete gap and vertex equations. For current-quark masses less than the scale
set by dynamical chiral symmetry breaking, the dependence of the
dressed-quark-gluon vertex on the current-quark mass is weak. The study employs
a vertex model whose diagrammatic content is explicitly enumerable. That
enables the systematic construction of a vertex-consistent Bethe-Salpeter
kernel and thereby an exploration of the consequences for the strong
interaction spectrum of attraction in the colour-octet channel. With rising
current-quark mass the rainbow-ladder truncation is shown to provide an
increasingly accurate estimate of a bound state's mass. Moreover, the
calculated splitting between vector and pseudoscalar meson masses vanishes as
the current-quark mass increases, which argues for the mass of the pseudoscalar
partner of the \Upsilon(1S) to be above 9.4 GeV. The absence of
colour-antitriplet diquarks from the strong interaction spectrum is contingent
upon the net amount of attraction in the octet projected quark-antiquark
scattering kernel. There is a window within which diquarks appear. The amount
of attraction suggested by lattice results is outside this domain.Comment: 22 pages, 12 figure
How Aromatic Fluorination Exchanges the Interaction Role of Pyridine with Carbonyl Compounds: The Formaldehyde Adduct
The rotational spectrum of the weakly bound complex pentafluoropyridineâ
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â
formaldehyde has been investigated using Fourier transform microwave spectroscopy. From the analysis of the rotational parameters of the parent species and of the 13C and 15N isotopologues, the structural arrangement of the adduct has been unambiguously established. The full ring fluorination of pyridine has a dramatic effect on its binding properties: It alters the electron density distribution at the Ï-cloud of pyridine creating a Ï-hole and changing its electron donor-acceptor capabilities. In the complex, formaldehyde lies above the aromatic ring with one of the oxygen lone pairs, as conventionally envisaged, pointing toward its centre. This lone pairâ
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Ï-hole interaction, reinforced by a weak CâHâ
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N interaction, indicates an exchange of the electron-acceptor roles of both molecules when compared to the pyridineâ
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formaldehyde adduct. Tunnelling doublets due to the internal rotation of formaldehyde have also been observed and analysed leading to a discussion on the competition between lone pairâ
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Ï-hole and Ïâ
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Ï stacking interactions
Dynamical Chiral Symmetry Breaking in Unquenched
We investigate dynamical chiral symmetry breaking in unquenched
using the coupled set of Dyson--Schwinger equations for the fermion and photon
propagators. For the fermion-photon interaction we employ an ansatz which
satisfies its Ward--Green--Takahashi identity. We present self-consistent
analytical solutions in the infrared as well as numerical results for all
momenta. In Landau gauge, we find a phase transition at a critical number of
flavours of . In the chirally symmetric phase the
infrared behaviour of the propagators is described by power laws with
interrelated exponents. For and we find small values for the
chiral condensate in accordance with bounds from recent lattice calculations.
We investigate the Dyson--Schwinger equations in other linear covariant gauges
as well. A comparison of their solutions to the accordingly transformed Landau
gauge solutions shows that the quenched solutions are approximately gauge
covariant, but reveals a significant amount of violation of gauge covariance
for the unquenched solutions.Comment: 33 pages, 8 figures, reference added, version to be published in
Phys. Rev.
Survey of J=0,1 mesons in a Bethe-Salpeter approach
The Bethe-Salpeter equation is used to comprehensively study mesons with
J=0,1 and equal-mass constituents for quark masses from the chiral limit to the
b-quark mass. The survey contains masses of the ground states in all
corresponding J^{PC} channels including those with "exotic" quantum numbers.
The emphasis is put on each particular state's sensitivity to the low- and
intermediate-momentum, i.e., long-range part of the strong interaction.Comment: 8 pages, 4 figure
A systematic approach to the Planck LFI end-to-end test and its application to the DPC Level 1 pipeline
The Level 1 of the Planck LFI Data Processing Centre (DPC) is devoted to the
handling of the scientific and housekeeping telemetry. It is a critical
component of the Planck ground segment which has to strictly commit to the
project schedule to be ready for the launch and flight operations. In order to
guarantee the quality necessary to achieve the objectives of the Planck
mission, the design and development of the Level 1 software has followed the
ESA Software Engineering Standards. A fundamental step in the software life
cycle is the Verification and Validation of the software. The purpose of this
work is to show an example of procedures, test development and analysis
successfully applied to a key software project of an ESA mission. We present
the end-to-end validation tests performed on the Level 1 of the LFI-DPC, by
detailing the methods used and the results obtained. Different approaches have
been used to test the scientific and housekeeping data processing. Scientific
data processing has been tested by injecting signals with known properties
directly into the acquisition electronics, in order to generate a test dataset
of real telemetry data and reproduce as much as possible nominal conditions.
For the HK telemetry processing, validation software have been developed to
inject known parameter values into a set of real housekeeping packets and
perform a comparison with the corresponding timelines generated by the Level 1.
With the proposed validation and verification procedure, where the on-board and
ground processing are viewed as a single pipeline, we demonstrated that the
scientific and housekeeping processing of the Planck-LFI raw data is correct
and meets the project requirements.Comment: 20 pages, 7 figures; this paper is part of the Prelaunch status LFI
papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jins
Anomaly in the stability limit of liquid helium 3
We propose that the liquid-gas spinodal line of helium 3 reaches a minimum at
0.4 K. This feature is supported by our cavitation measurements. We also show
that it is consistent with extrapolations of sound velocity measurements.
Speedy [J. Phys. Chem. 86, 3002 (1982)] previously proposed this peculiar
behavior for the spinodal of water and related it to a change in sign of the
expansion coefficient alpha, i. e. a line of density maxima. Helium 3 exhibits
such a line at positive pressure. We consider its extrapolation to negative
pressure. Our discussion raises fundamental questions about the sign of alpha
in a Fermi liquid along its spinodal.Comment: 5 pages, 3 figure
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