6,328 research outputs found
Approximating chiral SU(3) amplitudes
We construct large-N_c motivated approximate chiral SU(3) amplitudes of
next-to-next-to-leading order. The amplitudes are independent of the
renormalization scale. Fitting lattice data with those amplitudes allows for
the extraction of chiral coupling constants with the correct scale dependence.
The differences between approximate and full amplitudes are required to be at
most of the order of N^3LO contributions numerically. Applying the approximate
expressions to recent lattice data for meson decay constants, we determine
several chiral couplings with good precision. In particular, we obtain a value
for F_0, the meson decay constant in the chiral SU(3) limit, that is more
precise than all presently available determinations.Comment: 19 pages, 4 figures, improved presentation, results unchanged,
version to appear in EPJ
Chiral Perturbation Theory with Virtual Photons and Leptons
We construct a low-energy effective field theory which allows the full
treatment of isospin-breaking effects in semileptonic weak interactions. To
this end, we enlarge the particle spectrum of chiral perturbation theory with
virtual photons by including also the light leptons as dynamical degrees of
freedom. Using super-heat-kernel techniques, we determine the additional
one-loop divergences generated by the presence of virtual leptons and give the
full list of associated local counterterms. We illustrate the use of our
effective theory by applying it to the decays pi -> l nu_{l} and K -> l nu_{l}.Comment: 22 pages, no figure
Adjusting to Globalization: Challenges for the Canadian Banking System
The mid-1960s were the good old days for Canadian bankers before the Canadian banking system was opened up to foreign competition. Now it is a whole new competitive ball game as Edward P. Neufeld points out in his paper on the challenges that globalization poses for the Canadian banking system. He argues that the ability of Canadian institutions to withstand increasing foreign competition will depend on their economic efficiency relative to that of the encroaching competitors. In his view, the forces that have facilitated globalization of financial services have also made obsolete past measures of economies of scale and of the “optimum” size of financial institutions, and past guidelines concerning excessive domestic market concentration are no longer reliable. For Canadian financial institutions to experience solid growth in the future will require them to be internationally competitive at home and abroad. But unfortunately they have been slipping down the list of important international financial institutions as measured by the size of their assets and of their capital bases, and as a result their non-interest costs are 10 to 20 per cent higher than they would be if mergers were permitted. Otherwise, the forces of globalization will generate a persistent tendency towards increased foreign ownership of Canadian financial institutions, as has already begun to happen, and towards an increase in non-Canadian executives running them. Neufeld is very concerned that Bill C-8, which is the new legislation reforming the financial service sector passed this year, contains discrimina- tory measures that will undermine the international competitiveness of the Canadian banking system. These include: a restrictive and politicized bank merger policy, which risks preventing Canadian banks from achieving the economies of scale that their much larger international competitors are achieving; the continued prohibition against the distribution of life insurance through bank branches, which directly restricts competition in the Canadian market; the continued exclusion of the banks from the car leasing business, a business almost completely dominated by foreign institutions; and the threat in the bill directed at the large Canadian banks, and not at smaller competing institutions or foreign institutions located in Canada or entering the Canadian market through the Internet, that if they do not provide certain low-cost services they will be forced to do so. In Neufeld’s view, the most glaring weakness of the new policy as concerns competition is its failure to recognize clearly that by far the most important source of future competition will be large international institutions operating directly in Canada and through the Internet from outside Canada. He regards the merger process as flawed in that it is tortuous, and therefore inevitably subject to long delays, and risks being hostage to short-term political considerations. Neufeld believes that the key question that needs to be addressed is not whether Canadians will get the world-class financial services they require, because international competition will ensure that, but whether the services will be provided by Canadian banks or foreign financial institutions.Canada, Banking, Banks, Financial Services, Mergers, Market Concentration, Bill C-8
Radiative corrections to K_{l3} decays
We present a complete calculation of the K_{l3} decays K^+ --> pi^0 l^+ nu_l
and K^0 --> pi^- l^+ nu_l to O(p^4, (m_d-m_u) p^2, e^2 p^2) in chiral
perturbation theory with virtual photons and leptons. We introduce the concept
of generalized form factors and kinematical densities in the presence of
electromagnetism, and propose a possible treatment of the real photon emission
in K^+_{l3} decays. We illustrate our results by applying them to the
extraction of the Kobayashi--Maskawa matrix element |V_{us}| from the
experimental K^+_{e3} decay parameters.Comment: 13 page
A Herschel/HIFI Legacy Survey of HF and H2O in the Galaxy: Probing Diffuse Molecular Cloud Chemistry
We combine Herschel observations of a total of 12 sources to construct the
most uniform survey of HF and H2O in our Galactic disk. Both molecules are
detected in absorption along all sight lines. The high spectral resolution of
the Heterodyne Instrument for the Far-Infrared (HIFI) allows us to compare the
HF and H2O distributions in 47 diffuse cloud components sampling the disk. We
find that the HF and H2O velocity distributions follow each other almost
perfectly and establish that HF and H2O probe the same gas-phase volume. Our
observations corroborate theoretical predictions that HF is a sensitive tracer
of H2 in diffuse clouds, down to molecular fractions of only a few percent.
Using HF to trace H2 in our sample, we find that the N(H2O)-to-N(HF) ratio
shows a narrow distribution with a median value of 1.51. Our results further
suggest that H2O might be used as a tracer of H2 -within a factor 2.5- in the
diffuse interstellar medium. We show that the measured factor of ~2.5 variation
around the median is driven by true local variations in the H2O abundance
relative to H2 throughout the disk. The latter variability allows us to test
our theoretical understanding of the chemistry of oxygen-bearing molecules in
the diffuse gas. We show that both gas-phase and grain-surface chemistry are
required to reproduce our H2O observations. This survey thus confirms that
grain surface reactions can play a significant role in the chemistry occurring
in the diffuse interstellar medium n_H < 1000 cm^-3.Comment: 53 pages; 12 figures, accepted for publication in ApJ main journa
The IRAM-30m line survey of the Horsehead PDR: I. CF+ as a tracer of C+ and a measure of the Fluorine abundance
C+ is a key species in the interstellar medium but its 158 {\mu}m fine
structure line cannot be observed from ground-based telescopes. Current models
of fluorine chemistry predict that CF+ is the second most important fluorine
reservoir, in regions where C+ is abundant. We detected the J = 1-0 and J = 2-1
rotational lines of CF+ with high signal-to-noise ratio towards the PDR and
dense core positions in the Horsehead. Using a rotational diagram analysis, we
derive a column density of N(CF+) = (1.5 - 2.0) \times 10^12 cm^-2. Because of
the simple fluorine chemistry, the CF+ column density is proportional to the
fluorine abundance. We thus infer the fluorine gas-phase abundance to be F/H =
(0.6 - 1.5) \times 10^-8. Photochemical models indicate that CF+ is found in
the layers where C+ is abundant. The emission arises in the UV illuminated skin
of the nebula, tracing the outermost cloud layers. Indeed, CF+ and C+ are the
only species observed to date in the Horsehead with a double peaked line
profile caused by kinematics. We therefore propose that CF+, which is
detectable from the ground, can be used as a proxy of the C+ layers.Comment: Accepted to A&A, 4 pages, 4 figures, 2 table
Smooth-filamental transition of active tracer fields stirred by chaotic advection
The stationary-state spatial structure of interacting chemical fields is investigated in the nondiffusive limit. The evolution of fluid parcels is described by independent dynamical systems driven by chaotic advection. The distribution can be filamental or smooth depending on the relative strength of the dispersion due to chaotic advection and the stability of the chemical dynamics. We give the condition for the smooth-filamental transition and relate the Hölder exponent of the filamental structure to the Lyapunov exponents. Theoretical findings are illustrated by numerical experiments. © 1999 The American Physical Society.Funded by a Royal Society-NATO Postdoctoral Fellowship and C. L. was funded by CICYT projects (No. MAR95-1861 and No. MAR98-0840).Peer Reviewe
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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