20,614 research outputs found
Nonet Symmetry and Two-Body Decays of Charmed Mesons
The decay of charmed mesons into pseudoscalar (P) and vector (V) mesons is
studied in the context of nonet symmetry. We have found that it is badly broken
in the PP channels and in the P sector of the PV channels as expected from the
non-ideal mixing of the \eta and the \eta'. In the VV channels, it is also
found that nonet symmetry does not describe the data well. We have found that
this discrepancy cannot be attributed entirely to SU(3) breaking at the usual
level of 20--30%. At least one, or both, of nonet and SU(3) symmetry must be
very badly broken. The possibility of resolving the problem in the future is
also discussed.Comment: 9 pages, UTAPHY-HEP-
Development of design allowable data for Celion 6000/LARC-160, graphite/polyimide composite laminates
A design allowables test program was conducted on Celion 6000/LARC-160 graphite polyimide composite to establish material performance over a 116 K (-250 F) to 589 K (600 F) temperature range. Tension, compression, in-plane shear and short beam shear properties were determined for uniaxial, quasi-isotropic and + or - 45 deg laminates. Effects of thermal aging and moisture saturation on mechanical properties were also evaluated. Celion 6000/LARC-160 graphite/polyimide can be considered an acceptable material system for structural applications to 589 K (600 F)
The measurement errors in the Swift-UVOT and XMM-OM
The probability of photon measurement in some photon counting
instrumentation, such as the Optical Monitor on the XMM-Newton satellite, and
the UVOT on the Swift satellite, does not follow a Poisson distribution due to
the detector characteristics, but a Binomial distribution. For a single-pixel
approximation, an expression was derived for the incident countrate as a
function of the measured count rate by Fordham, Moorhead and Galbraith (2000).
We show that the measured countrate error is binomial, and extend their
formalism to derive the error in the incident count rate. The error on the
incident count rate at large count rates is larger than the Poisson-error of
the incident count rate.Comment: 4 pages, 2 postscript figures, submitted to MNRA
Collision of High Frequency Plane Gravitational and Electromagnetic Waves
We study the head-on collision of linearly polarized, high frequency plane
gravitational waves and their electromagnetic counterparts in the
Einstein-Maxwell theory. The post-collision space-times are obtained by solving
the vacuum Einstein-Maxwell field equations in the geometrical optics
approximation. The head-on collisions of all possible pairs of these systems of
waves is described and the results are then generalised to non-linearly
polarized waves which exhibit the maximum two degrees of freedom of
polarization.Comment: Latex file, 17 pages, accepted for publication in International
Journal of Modern Physics
Sufficient conditions for the existence of Q-balls in gauge theories
We formulate a set of simple sufficient conditions for the existence of
Q-balls in gauge theories.Comment: 5 page
X-ray and UV observations of V751 Cyg in an optical high state
Aims: The VY Scl system (anti-dwarf nova) V751 Cyg is examined following a
claim of a super-soft spectrum in the optical low state. Methods: A
serendipitous XMM-Newton X-ray observation and, 21 months later, Swift X-ray
and UV observations, have provided the best such data on this source so far.
These optical high-state datasets are used to study the flux and spectral
variability of V751 Cyg. Results: Both the XMM-Newton and Swift data show
evidence for modulation of the X-rays for the first time at the known 3.467 hr
orbital period of V751 Cyg. In two Swift observations, taken ten days apart,
the mean X-ray flux remained unchanged, while the UV source brightened by half
a magnitude. The X-ray spectrum was not super-soft during the optical high
state, but rather due to multi-temperature optically thin emission, with
significant (10^{21-22} cm^-2) absorption, which was higher in the observation
by Swift than that of XMM-Newton. The X-ray flux is harder at orbital minimum,
suggesting that the modulation is related to absorption, perhaps linked to the
azimuthally asymmetric wind absorption seen previously in H-alpha.Comment: 6 pages, 9 figures, accepted for publication in A&
Generalized Symmetries of Impulsive Gravitational Waves
We generalize previous \cite{AiBa2} work on the classification of
() symmetries of plane-fronted waves with an impulsive profile. Due
to the specific form of the profile it is possible to extend the group of
normal-form-preserving diffeomorphisms to include non-smooth transformations.
This extension entails a richer structure of the symmetry algebra generated by
the (non-smooth) Killing vectors.Comment: 18 pages, latex2e, no figure
Searching for the MSW Enhancement
We point out that the length scale associated with the MSW effect is the
radius of the Earth. Therefore to verify matter enhancement of neutrino
oscillations, it will be necessary to study neutrinos passing through the
Earth. For the parameters of MSW solutions to the solar neutrino problem, the
only detectable effects occur in a narrow band of energies from 5 to 10 MeV. We
propose that serious consideration be given to mounting an experiment at a
location within 9.5 degrees of the equator.Comment: 10 pages, RevTe
- âŠ