2,663 research outputs found
Radio/X-ray Offsets of Large Scale Jets Caused by Synchrotron Time Lags
In the internal shock scenario, we argue that electrons in most kpc (or even
larger) scale jets can be accelerated to energies high enough to emit
synchrotron X-rays, if shocks exist on these scales. These high energy
electrons emit synchrotron radiation at high frequencies and cool as they
propagate downstream along the jet, emitting at progressively lower frequencies
and resulting in time lags and hence radio/X-ray (and optical/X-ray if the
optical knot is detectable) offsets at bright knots, with the centroids of
X-ray knots being closer to the core. Taking into account strong effects of jet
expansion, the behaviour of radio/X-ray and optical/X-ray offsets at bright
knots in M87, Cen A, 3C 66B, 3C 31, 3C 273, and PKS 1127-145 is consistent with
that of synchrotron time lags due to radiative losses. This suggests that the
large scale X-ray and optical jets in these sources are due to synchrotron
emission.Comment: 4 pages, Accepted for publication in ApJ Letter
Unitarity issue in BTZ black holes
We study the wave equation for a massive scalar in three-dimensional
AdS-black hole spacetimes to understand the unitarity issues in a semiclassical
way. Here we introduce four interesting spacetimes: the non-rotating BTZ black
hole (NBTZ), pure AdS spacetime (PADS), massless BTZ black hole (MBTZ), and
extremal BTZ black hole (EBTZ). Our method is based on the potential analysis
and solving the wave equation to find the condition for the frequency
exactly. In the NBTZ case, one finds the quasinormal (complex and discrete)
modes which signals for a non-unitary evolution. Real and discrete modes are
found for the PADS case, which means that it is unitary obviously. On the other
hand, we find real and continuous modes for the two extremal black holes of
MBTZ and EBTZ. It suggests that these could be candidates for the unitary
system.Comment: 14 pages, contracted version to appear in MPL
Hom-Lie color algebra structures
This paper introduces the notion of Hom-Lie color algebra, which is a natural
general- ization of Hom-Lie (super)algebras. Hom-Lie color algebras include
also as special cases Lie (super) algebras and Lie color algebras. We study the
homomorphism relation of Hom-Lie color algebras, and construct new algebras of
such kind by a \sigma-twist. Hom-Lie color admissible algebras are also defined
and investigated. They are finally classified via G-Hom-associative color
algebras, where G is a subgroup of the symmetric group S_3.Comment: 16 page
Cosmic holographic bounds with UV and IR cutoffs
We introduce the cosmic holographic bounds with two UV and IR cutoff scales,
to deal with both the inflationary universe in the past and dark energy in the
future. To describe quantum fluctuations of inflation on sub-horizon scales, we
use the Bekenstein-Hawking energy bound. However, it is not justified that the
D-bound is satisfied with the coarse-grained entropy. The Hubble bounds are
introduced for classical fluctuations of inflation on super-horizon scales. It
turns out that the Hubble entropy bound is satisfied with the entanglement
entropy and the Hubble temperature bound leads to a condition for the slow-roll
inflation. In order to describe the dark energy, we introduce the holographic
energy density which is the one saturating the Bekenstein-Hawking energy bound
for a weakly gravitating system. Here the UV (IR) cutoff is given by the Planck
scale (future event horizon), respectively. As a result, we find the close
connection between quantum and classical fluctuations of inflation, and dark
energy.Comment: 15page
Retinoic Acid Differentially Regulates the Migration of Innate Lymphoid Cell Subsets to the Gut
SummaryDistinct groups of innate lymphoid cells (ILCs) such as ILC1, ILC2, and ILC3 populate the intestine, but how these ILCs develop tissue tropism for this organ is unclear. We report that prior to migration to the intestine ILCs first undergo a “switch” in their expression of homing receptors from lymphoid to gut homing receptors. This process is regulated by mucosal dendritic cells and the gut-specific tissue factor retinoic acid (RA). This change in homing receptors is required for long-term population and effector function of ILCs in the intestine. Only ILC1 and ILC3, but not ILC2, undergo the RA-dependent homing receptor switch in gut-associated lymphoid tissues. In contrast, ILC2 acquire gut homing receptors in a largely RA-independent manner during their development in the bone marrow and can migrate directly to the intestine. Thus, distinct programs regulate the migration of ILC subsets to the intestine for regulation of innate immunity
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