6,425 research outputs found
Radiative Non-Leptonic Kaon Decays
We investigate to what extent DANE will be able to test the Standard
Model in the confinement regime with radiative kaon decays. We concentrate on
processes which can be detected at DANE and we review briefly those
decays where only upper limits can be expected. The Standard Model predictions
for these decays are analyzed in the framework of chiral perturbation theory.Comment: 41 pages, latex file, 10 figures added in a separate uufil
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
Electromagnetism in nonleptonic weak interactions
We construct a low-energy effective field theory that permits the complete
treatment of isospin-breaking effects in nonleptonic weak interactions to
next-to-leading order. To this end, we enlarge the chiral Lagrangian describing
strong and Delta S=1 weak interactions by including electromagnetic terms with
the photon as additional dynamical degree of freedom. The complete and minimal
list of local terms at next-to-leading order is given. We perform the one-loop
renormalization at the level of the generating functional and specialize to K
-> pi pi decays.Comment: 17 pages, 1 figure; 2 references added, final version for publication
in Nucl. Phys.
Isospin violation in epsilon'
On the basis of a next-to-leading-order calculation in chiral perturbation
theory, the first complete analysis of isospin breaking for direct CP violation
in K^0 -> 2 pi decays is performed. We find a destructive interference between
three different sources of isospin violation in the CP violation parameter
epsilon'. Within the uncertainties of large-N_c estimates for the low-energy
constants, the isospin violating correction for epsilon' is below 15 %.Comment: 4 page
The chemistry of fluorine-bearing molecules in diffuse and dense interstellar gas clouds
We present a theoretical investigation of the chemistry of fluorine-bearing
molecules in diffuse and dense interstellar gas clouds. The chemistry of
interstellar fluorine is qualitatively different from that of any other
element, because - unlike the neutral atoms of any other element found in
diffuse or dense molecular clouds - atomic fluorine undergoes an exothermic
reaction with molecular hydrogen. Over a wide range of conditions attained
within interstellar gas clouds, the product of that reaction - hydrogen
fluoride - is predicted to be the dominant gas-phase reservoir of interstellar
fluorine nuclei. Our model predicts HF column densities ~ 1.E+13 cm-2 in dark
clouds and column densities as large as 1.E-11 cm-2 in diffuse interstellar gas
clouds with total visual extinctions as small as 0.1 mag. Such diffuse clouds
will be detectable by means of absorption line spectroscopy of the J = 1 - 0
transition at 243.2 micron using the Stratospheric Observatory for Infrared
Astronomy (SOFIA) and the Herschel Space Observatory (HSO). The CF+ ion is
predicted to be the second most abundant fluorine-bearing molecule, with
typical column densities a factor ~ 100 below those of HF; with its lowest two
rotational transitions in the millimeter-wave spectral region, CF+ may be
detectable from ground-based observatories. HF absorption in quasar spectra is
a potential probe of molecular gas at high redshift, providing a possible
bridge between the UV/optical observations capable of probing H2 in low column
density systems and the radio/millimeter-wavelength observations that probe
intervening molecular clouds of high extinction and large molecular fraction;
at redshifts beyond ~ 0.3, HF is potentially detectable from ground-based
submillimeter observatories in several atmospheric transmission windows.Comment: 34 pages, including 11 figures (10 color), accepted for publication
in Ap
Discovery of Water Vapor in the High-redshift Quasar APM 08279+5255 at z = 3.91
We report a detection of the excited 2_(20)-2_(11) rotational transition of para-H_2O in APM 08279+5255 using the IRAM Plateau de Bure Interferometer. At z = 3.91, this is the highest-redshift detection of interstellar water to date. From large velocity gradient modeling, we conclude that this transition is predominantly radiatively pumped and on its own does not provide a good estimate of the water abundance. However, additional water transitions are predicted to be detectable in this source, which would lead to an improved excitation model. We also present a sensitive upper limit for the hydrogen fluoride (HF) J = 1-0 absorption toward APM 08279+5255. While the face-on geometry of this source is not favorable for absorption studies, the lack of HF absorption is still puzzling and may be indicative of a lower fluorine abundance at z = 3.91 compared with the Galactic interstellar medium
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