46,128 research outputs found
Noncommutative Einstein-Maxwell pp-waves
The field equations coupling a Seiberg-Witten electromagnetic field to
noncommutative gravity, as described by a formal power series in the
noncommutativity parameters , is investigated. A large
family of solutions, up to order one in , describing
Einstein-Maxwell null pp-waves is obtained. The order-one contributions can be
viewed as providing noncommutative corrections to pp-waves. In our solutions,
noncommutativity enters the spacetime metric through a conformal factor and is
responsible for dilating/contracting the separation between points in the same
null surface. The noncommutative corrections to the electromagnetic waves,
while preserving the wave null character, include constant polarization, higher
harmonic generation and inhomogeneous susceptibility. As compared to pure
noncommutative gravity, the novelty is that nonzero corrections to the metric
already occur at order one in .Comment: 19 revtex pages. One refrence suppressed, two references added. Minor
wording changes in the abstract, introduction and conclusio
Light- and strange-quark mass dependence of the meson revisited
Recent lattice data on -scattering phase shifts in the
vector-isovector channel, pseudoscalar meson masses and decay constants for
strange-quark masses smaller or equal to the physical value allow us to study
the strangeness dependence of these observables for the first time. We perform
a global analysis on two kind of lattice trajectories depending on whether the
sum of quark masses or the strange-quark mass is kept fixed to the physical
point. The quark mass dependence of these observables is extracted from
unitarized coupled-channel one-loop Chiral Perturbation Theory. This analysis
guides new predictions on the meson properties over trajectories
where the strange-quark mass is lighter than the physical mass, as well as on
the SU(3) symmetric line. As a result, the light- and strange-quark mass
dependence of the meson parameters are discussed and precise values
of the Low Energy Constants present in unitarized one-loop Chiral Perturbation
Theory are given. Finally, the current discrepancy between two- and
three-flavor lattice results for the meson is studied.Comment: 44 pages, 41 figures, 11 table
The molecular envelope of CRL 618: A new model based on Herschel/HIFI observations
We study the physical properties and molecular excitation of the different
warm gas components found in the protoplanetary nebula CRL 618. We revise our
previous Herschel/HIFI observations, which consist of several 12CO and 13CO
lines in the far-infrared/sub-mm band. These data have been re-analyzed in
detail by improving calibration, the signal-to-noise-ratio, and baseline
substraction. We identify the contributions of the different nebular components
to the line profiles. We have used a spatio-kinematical model to better
constrain the temperature, density, and kinematics of the molecular components
probed by the improved CO observations. The 12CO and 13CO J=16-15, J=10-9, and
J=6-5 transitions are detected in this source. The line profiles present a
composite structure showing spectacular wings in some cases, which become
dominant as the energy level increases. Our analysis of the high-energy CO
emission with the already known low-energy J=2-1 and J=1-0 lines confirms that
the high-velocity component, or fast bipolar outflow, is hotter than previously
estimated with a typical temperature of ~300 K. This component may then be an
example of a very recent acceleration of the gas by shocks that has not yet
cooled down. We also find that the dense central core is characterized by a
very low expansion velocity, ~5 km/s, and a strong velocity gradient. We
conclude that this component is very likely to be the unaltered circumstellar
layers that are lost in the last AGB phase, where the ejection velocity is
particularly low. The physical properties of the other two nebular components,
the diffuse halo and the double empty shell, more or less agrees with the
estimations derived in previous models.Comment: Accepted for publication in Astronomy & Astrophysics. 8 pages, 3
figure
Strange resonance poles from scattering below 1.8 GeV
In this work we present a determination of the mass, width and coupling of
the resonances that appear in kaon-pion scattering below 1.8 GeV. These are:
the much debated scalar -meson, nowdays known as , the
scalar , the and vectors, the spin-two
as well as the spin-three . The parameters will be
determined from the pole associated to each resonance by means of an analytic
continuation of the scattering amplitudes obtained in a recent and
precise data analysis constrained with dispersion relations, which were not
well satisfied in previous analyses. This analytic continuation will be
performed by means of Pad\'e approximants, thus avoiding a particular model for
the pole parameterization. We also pay particular attention to the evaluation
of uncertainties.Comment: 13 pages, 12 figures. Accepted version to appear in Eur. Phys. J. C.
Clarifications and references added, minor typos correcte
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