7,952 research outputs found
Chern-Simons--Antoniadis-Savvidy forms and standard supergravity
In the context of the so called the Chern--Simons--Antoniadis--Savvidy
(ChSAS) forms, we use the methods for FDA decomposition in 1-forms to construct
a four-dimensional ChSAS supergravity action for the Maxwell superalgebra. On
the another hand, we use the Extended Cartan Homotopy Formula to find a method
that allows the separation of the ChSAS action into bulk and boundary
contributions and permits the splitting of the bulk Lagrangian into pieces that
reflect the particular subspace structure of the gauge algebra.Comment: 14 page
Generalized Galilean Algebras and Newtonian Gravity
The non-relativistic versions of the generalized Poincar\'{e} algebras and
generalized -Lorentz algebras are obtained. This non-relativistic algebras
are called, generalized Galilean algebras type I and type II and denoted by
and
respectively. Using a generalized In\"{o}n\"{u}--Wigner contraction procedure
we find that the generalized Galilean algebras type I can be obtained from the
generalized Galilean algebras type II. The -expansion procedure allows us to
find the algebra from the Newton--Hooke
algebra with central extension. The procedure developed in Ref. \cite{newton}
allow us to show that the non-relativistic limit of the five dimensional
Einstein--Chern--Simons gravity is given by a modified version of the Poisson
equation. The modification could be compatible with the effects of Dark Matter,
which leads us to think that Dark Matter can be interpreted as a
non-relativistic limit of Dark Energy.Comment: 16 pages, no figures in 755 (2016) 433-43
Spectroscopy of blue horizontal branch stars in NGC 6656 (M22)
Recent investigations revealed very peculiar properties of blue horizontal
branch (HB) stars in \omega Centauri, which show anomalously low surface
gravity and mass compared to other clusters and to theoretical models. \omega
Centauri, however, is a very unusual object, hosting a complex mix of multiple
stellar populations with different metallicity and chemical abundances. We
measured the fundamental parameters (temperature, gravity, and surface helium
abundance) of a sample of 71 blue HB stars in M22, with the aim of clarifying
if the peculiar results found in \omega Cen are unique to this cluster. M22
also hosts multiple sub-populations of stars with a spread in metallicity,
analogous to \omega Cen. The stellar parameters were measured on low-resolution
spectra fitting the Balmer and helium lines with a grid of synthetic spectra.
From these parameters, the mass and reddening were estimated. Our results on
the gravities and masses agree well with theoretical expectations, matching the
previous measurements in three "normal" clusters. The anomalies found in \omega
Cen are not observed among our stars. A mild mass underestimate is found for
stars hotter than 14\,000 K, but an exact analogy with \omega Cen cannot be
drawn. We measured the reddening in the direction of M22 with two independent
methods, finding E(B-V)=0.35 \pm 0.02 mag, with semi-amplitude of the maximum
variation \Delta(E(B-V))=0.06 mag, and an rms intrinsic dispersion of
\sigma(E(B-V))=0.03 mag.Comment: 11 pages, 9 Postscript figure
Correlations in the QPO Frequencies of Low Mass X-Ray Binaries and the Relativistic Precession Model
A remarkable correlation between the centroid frequencies of quasi periodic
oscillations, QPOs, (or peaked noise components) from low mass X-ray binaries,
has been recently discovered by Psaltis, Belloni and van der Klis (1999). This
correlation extends over nearly 3 decades in frequency and encompasses both
neutron star and black hole candidate systems. We discuss this result in the
light of the relativistic precession model, which has been proposed to
interpret the kHz QPOs as well as some of the lower frequency QPOs of neutron
star low mass X-ray binaries of the Atoll and Z classes. Unlike other models
the relativistic precession model does not require the compact object to be a
neutron star and can be applied to black hole candidates as well. We show that
the predictions of the relativistic precession model match both the value and
dependence of the correlation to a very good accuracy without resorting to
additional assumptions.Comment: To appear in ApJ Letters. AASTEX Latex v. 5.0, 1 figure not include
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