4,832 research outputs found
The Coupling of Shape Dynamics to Matter
Shape Dynamics (SD) is a theory dynamically equivalent to vacuum General
Relativity (GR), which has a different set of symmetries. It trades refoliation
invariance, present in GR, for local 3-dimensional conformal invariance. This
contribution to the Loops 11 conference addresses one of the more urgent
questions regarding the equivalence: is it possible to incorporate normal
matter in the new framework? The answer is yes, in certain regimes. We present
general criteria for coupling and apply it to a few examples.The outcome
presents bounds and conditions on scalar densities (such as the Higgs potential
and the cosmological constant) not present in GR.Comment: 4 pages. Contribution to Loops '11 conference in Madrid, to appear in
Journal of Physics: Conference Series (JPCS
Spherically symmetric loop quantum gravity: analysis of improved dynamics
We study the "improved dynamics" for the treatment of spherically symmetric
space-times in loop quantum gravity introduced by Chiou {\em et al.} in analogy
with the one that has been constructed by Ashtekar, Pawlowski and Singh for the
homogeneous space-times. In this dynamics the polymerization parameter is a
well motivated function of the dynamical variables, reflecting the fact that
the quantum of area depends on them. Contrary to the homogeneous case, its
implementation does not trigger undesirable physical properties. We identify
semiclassical physical states in the quantum theory and derive the
corresponding effective semiclassical metrics. We then discuss some of their
properties. Concretely, the space-time approaches sufficiently fast the
Schwarzschild geometry at low curvatures. Besides, regions where the
singularity is in the classical theory get replaced by a regular but discrete
effective geometry with finite and Planck order curvature, regardless of the
mass of the black hole. This circumvents trans-Planckian curvatures that
appeared for astrophysical black holes in the quantization scheme without the
improvement. It makes the resolution of the singularity more in line with the
one observed in models that use the isometry of the interior of a Schwarzschild
black hole with the Kantowski--Sachs loop quantum cosmologies. One can observe
the emergence of effective violations of the null energy condition in the
interior of the black hole as part of the mechanism of the elimination of the
singularity.Comment: 26 pages, 8 figure
Ca II triplet spectroscopy of small magellanic cloud red giants. II. abundances for a sample of field stars
We have obtained metallicities of ∼360 red giant stars distributed in 15 Small Magellanic Cloud (SMC) fields from near-infrared spectra covering the Ca II triplet lines using the VLT + FORS2. The errors of the derived [Fe/H] values range from 0.09 to 0.35 dex per star, with a mean of 0.17 dex. The metallicity distribution (MD) of the whole sample shows a mean value of [Fe/H] = -1.00 ± 0.02, with a dispersion of 0.32 0.01, in agreement with global mean [Fe/H] values found in previous studies. We find no evidence of a metallicity gradient in the SMC. In fact, on analyzing the MD of each field, we derived mean values of [Fe/H] = -0.99 ± 0.08 and [Fe/H] = -1.02 ± 0.07 for fields located closer and farther than 4° from the center of the galaxy, respectively. In addition, there is a clear tendency for the field stars to be more metal-poor than the corresponding cluster they surround, independent of their positions in the galaxy and of the clusters' age. We argue that this most likely stems from the field stars being somewhat older and therefore somewhat more metal-poor than most of our clusters. © 2010. The American Astronomical Society.Fil: Parisi, Maria Celeste. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Geisler, Doug. Universidad de Concepción; ChileFil: Grocholski, A. J.. University of Florida; Estados Unidos. Space Telescope Science Institute; Estados UnidosFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Sarajedini, A.. University of Florida; Estados Unido
Tracking the Evolution of A Coherent Magnetic Flux Rope Continuously from the Inner to the Outer Corona
The magnetic flux rope (MFR) is believed to be the underlying magnetic
structure of coronal mass ejections (CMEs). However, it remains unclear how an
MFR evolves into and forms the multi-component structure of a CME. In this
paper, we perform a comprehensive study of an extreme-ultraviolet (EUV) MFR
eruption on 2013 May 22 by tracking its morphological evolution, studying its
kinematics, and quantifying its thermal property. As EUV brightenings begin,
the MFR starts to rise slowly and shows helical threads winding around an axis.
Meanwhile, cool filamentary materials descend spirally down to the
chromosphere. These features provide direct observational evidence of
intrinsically helical structure of the MFR. Through detailed kinematical
analysis, we find that the MFR evolution experiences two distinct phases: a
slow rise phase and an impulsive acceleration phase. We attribute the first
phase to the magnetic reconnection within the quasi-separatrix-layers
surrounding the MFR, and the much more energetic second phase to the fast
magnetic reconnection underneath the MFR. We suggest that the transition
between these two phases be caused by the torus instability. Moreover, we
identify that the MFR evolves smoothly into the outer corona and appears as a
coherent structure within the white light CME volume. The MFR in the outer
corona was enveloped by bright fronts that originated from plasma pile-up in
front of the expanding MFR. The fronts are also associated with the preceding
sheath region followed the outmost MFR-driven shock.Comment: 9 pages, 6 figures, and 1 table, accepted by ApJ; any comments are
welcome
Loss of redundant gene expression after polyploidization in plants
Based on chromosomal location data of genes encoding 28 biochemical systems in allohexaploid wheat,Triticum aestivum L. (genomes AABBDD), it is concluded that the proportions of systems controlled by triplicate, duplicate, and single loci are 57%, 25%, and 18% respectively
The GALEX View of "Boyajian's Star" (KIC 8462852)
The enigmatic star KIC 8462852, informally known as "Boyajian's Star", has
exhibited unexplained variability from both short timescale (days) dimming
events, and years-long fading in the Kepler mission. No single physical
mechanism has successfully explained these observations to date. Here we
investigate the ultraviolet variability of KIC 8462852 on a range of timescales
using data from the GALEX mission that occurred contemporaneously with the
Kepler mission. The wide wavelength baseline between the Kepler and GALEX data
provides a unique constraint on the nature of the variability. Using 1600
seconds of photon-counting data from four GALEX visits spread over 70 days in
2011, we find no coherent NUV variability in the system on 10-100 second or
months timescales. Comparing the integrated flux from these 2011 visits to the
2012 NUV flux published in the GALEX-CAUSE Kepler survey, we find a 3% decrease
in brightness for KIC 8462852. We find this level of variability is
significant, but not necessarily unusual for stars of similar spectral type in
the GALEX data. This decrease coincides with the secular optical fading
reported by Montet & Simon (2016). We find the multi-wavelength variability is
somewhat inconsistent with typical interstellar dust absorption, but instead
favors a R = 5.0 0.9 reddening law potentially from circumstellar
dust.Comment: 8 pages, 4 figures, ApJ Accepte
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