6,317 research outputs found
Chiral QCD, General QCD Parameterization and Constituent Quark Models
Several recent papers -using effective QCD chiral Lagrangians- reproduced
results obtained with the general QCD parameterization (GP). These include the
baryon 8+10 mass formula, the octet magnetic moments and the coincidental
nature of the "perfect" -3/2 ratio between the magnetic moments of p and n.
Although we anticipated that the GP covers the case of chiral treatments, the
above results explicitly exemplify this fact. Also we show by the GP that -in
any model or theory (chiral or non chiral) reproducing the results of exact
QCD- the Franklin (Coleman Glashow) sum rule for the octet magnetic moments
must be violated.Comment: 10 pages, Latex; abridged version (same results), removed some
reference
Sudden To Adiabatic Transition in Beta Decay
We discuss effects in beta decays at very low beta energies, of the order of
the kinetic energies of atomic electrons. As the beta energy is lowered the
atomic response changes from sudden to adiabatic. As a consequence, the beta
decay rate increases slightly and the ejection of atomic electrons (shake off)
and subsequent production of X rays is turned off. We estimate the transition
energy and the change in decay rate. The rate increase is largest in heavy
atoms, which have a small Q value in their decay. The X ray switch-off is
independent of Q value.Comment: 6 pages LaTe
Analysis of dynamical corrections to baryon magnetic moments
We present and analyze QCD corrections to the baryon magnetic moments in
terms of the one-, two-, and three-body operators which appear in the effective
field theory developed in our recent papers. The main corrections are extended
Thomas-type corrections associated with the confining interactions in the
baryon. We investigate the contributions of low-lying angular excitations to
the moments quantitatively and show that they are completely negligible. When
the QCD corrections are combined with the non-quark model contributions of the
meson loops, we obtain a model which describes the moments within a mean
deviation of 0.04 . The nontrivial interplay of the two types of
corrections to the quark-model moments is analyzed in detail, and explains why
the quark model is so successful. In the course of these calculations, we
parametrize the general spin structure of the baryon wave functions
in a form which clearly displays the symmetry properties and the internal
angular momentum content of the wave functions, and allows us to use spin-trace
methods to calculate the many spin matrix elements which appear in the
expressions for the moments. This representation may be useful elsewhere.Comment: 32 pages, 3 figures, submitted to Phys. Rev.
Perturbative reliability of the Higgs-boson coupling in the standard electroweak model
We apply Pade summation to the \beta(\lambda) function for the quartic Higgs
coupling \lambda in the standard electroweak model. We use the \beta function
calculated to five loops in the minimal subtraction scheme to demonstrate the
improvement resulting from the summation, and then apply the method to the more
physical on-mass-shell renormalization scheme where \beta is known to three
loops. We conclude that the OMS \beta function and the running coupling
\lambda(\mu) are reliably known over the range of energies and Higgs-boson
masses of current interest.Comment: 14 pages, RevTeX, 6 figure
The effect of vacuum polarisation on muon-proton scattering at small energies and angles
We give a compact expression for the unpolarised differential cross section
for muon-proton scattering in the one photon exchange approximation. The effect
of adding the vacuum polarisation amplitude to the no-spin-flip amplitude for
one photon exchange is calculated at small energies and scattering angles and
is found to be negligible for present experiments.Comment: 6 pages, one figur
A three-dimensional full Stokes model of the grounding line dynamics: effect of a pinning point beneath the ice shelf
The West Antarctic ice sheet is confined by a large area of ice shelves, fed by inland ice through fast flowing ice streams. The dynamics of the grounding line, which is the line-boundary between grounded ice and the downstream ice shelf, has a major influence on the dynamics of the whole ice sheet. However, most ice sheet models use simplifications of the flow equations, as they do not include all the stress components, and are known to fail in their representation of the grounding line dynamics. Here, we present a 3-D full Stokes model of a marine ice sheet, in which the flow problem is coupled with the evolution of the upper and lower free surfaces, and the position of the grounding line is determined by solving a contact problem between the shelf/sheet lower surface and the bedrock. Simulations are performed using the open-source finite-element code Elmer/Ice within a parallel environment. The model's ability to cope with a curved grounding line and the effect of a pinning point beneath the ice shelf are investigated through prognostic simulations. Starting from a steady state, the sea level is slightly decreased to create a contact point between a seamount and the ice shelf. The model predicts a dramatic decrease of the shelf velocities, leading to an advance of the grounding line until both grounded zones merge together, during which an ice rumple forms above the contact area at the pinning point. Finally, we show that once the contact is created, increasing the sea level to its initial value does not release the pinning point and has no effect on the ice dynamics, indicating a stabilising effect of pinning points
Octet Magnetic Moments with Null Instantons and Semibosonized Nambu-Jona-Lasinio Model
It is shown that the difference between the magnetic moment results in the
quark model with null instantons and semibosonized Nambu-Jona-Lasinio model
lies in the description of the magnetic moment of the -hyperon.Comment: RevTex, 6 pages, submitted to Progr.Theor.Phy
Extragalactic database. VII Reduction of astrophysical parameters
The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main
astrophysical parameters for more than 100,000 galaxies. The most common names
are compiled allowing users to recover quickly any galaxy. All these measured
astrophysical parameters are first reduced to a common system according to well
defined reduction formulae leading to mean homogeneized parameters. Further,
these parameters are also transformed into corrected parameters from widely
accepted models. For instance, raw 21-cm line widths are transformed into mean
standard widths after correction for instrumental effect and then into maximum
velocity rotation properly corrected for inclination and non-circular velocity.
This paper presents the reduction formulae for each parameter: coordinates,
morphological type and luminosity class, diameter and axis ratio, apparent
magnitude (UBV, IR, HI) and colors, maximum velocity rotation and central
velocity dispersion, radial velocity, mean surface brightness, distance modulus
and absolute magnitude, and group membership. For each of these parameters
intermediate quantities are given: galactic extinction, inclination,
K-correction etc..
All these parameters are available from direct connexion to LEDA (telnet
lmc.univ-lyon1.fr, login: leda, no passwd
OR http://www-obs.univ-lyon1.fr/leda ) and distributed on a standard CD-ROM
(PGC-ROM 1996) by the Observatoire de Lyon via the CNRS (mail to
[email protected]).Comment: 13 pages, 12 figures. The CDROM of the extragalactic database LEDA is
available by mailing to: [email protected]
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