3,643 research outputs found
Chandra Observations of ULIRGs: Extended Hot Gas Halos in Merging Galaxies
We study the properties of hot gaseous halos in 10 nearby ultraluminous IRAS
galaxies observed with the ACIS instrument on board Chandra. For all sample
galaxies, diffuse soft X-ray emissions are found within ~10 kpc of the central
region; their spectra are well fitted by a MEKAL model plus emission lines from
alpha-elements and other ions. The temperature of the hot gas is about 0.7 keV
and metallicity is about 1 solar. Outside the central region, extended hot
gaseous halos are found for nine out of the ten ULIRGs. Most spectra of these
extended halos can be fitted with a MEKAL model with a temperature of about 0.6
keV and a low metallicity (~ 0.1 solar). We discuss the implications of our
results on the origin of X-ray halos in elliptical galaxies and the feedback
processes associated with starbursts.Comment: 31 pages, 6 figuers, ApJ in press, accepted versio
Penrose limits of Lie Branes and a Nappi--Witten braneworld
Departing from the observation that the Penrose limit of AdS_3 x S^3 is a
group contraction in the sense of Inonu and Wigner, we explore the relation
between the symmetric D-branes of AdS_3 x S^3 and those of its Penrose limit, a
six-dimensional symmetric plane wave analogous to the four-dimensional
Nappi--Witten spacetime. Both backgrounds are Lie groups admitting bi-invariant
lorentzian metrics and symmetric D-branes wrap their (twisted) conjugacy
classes. We determine the (twisted and untwisted) symmetric D-branes in the
plane wave background and we prove the existence of a space-filling D5-brane
and, separately, of a foliation by D3-branes with the geometry of the
Nappi--Witten spacetime which can be understood as the Penrose limit of the
AdS_2 x S^2 D3-brane in AdS_3 x S^3. Parenthetically we also derive a simple
criterion for a symmetric plane wave to be isometric to a lorentzian Lie group.
In particular we observe that the maximally supersymmetric plane wave in IIB
string theory is isometric to a lorentzian Lie group, whereas the one in
M-theory is not.Comment: 21 pages (v2: references added
Parallelisable Heterotic Backgrounds
We classify the simply-connected supersymmetric parallelisable backgrounds of
heterotic supergravity. They are all given by parallelised Lie groups admitting
a bi-invariant lorentzian metric. We find examples preserving 4, 8, 10, 12, 14
and 16 of the 16 supersymmetries.Comment: 17 pages, AMSLaTe
Supersymmetry and homogeneity of M-theory backgrounds
We describe the construction of a Lie superalgebra associated to an arbitrary
supersymmetric M-theory background, and discuss some examples. We prove that
for backgrounds with more than 24 supercharges, the bosonic subalgebra acts
locally transitively. In particular, we prove that backgrounds with more than
24 supersymmetries are necessarily (locally) homogeneous.Comment: 19 pages (Erroneous Section 6.3 removed from the paper.
AGN heating, thermal conduction and Sunyaev-Zeldovich effect in galaxy groups and clusters
(abridged) We investigate in detail the role of active galactic nuclei on the
physical state of the gas in galaxy groups and clusters, and the implications
for anisotropy in the CMB from Sunyaev-Zeldovich effect. We include the effect
of thermal conduction, and find that the resulting profiles of temperature and
entropy are consistent with observations. Unlike previously proposed models,
our model predicts that isentropic cores are not an inevitable consequence of
preheating. The model also reproduces the observational trend for the density
profiles to flatten in lower mass systems. We deduce the energy E_agn required
to explain the entropy observations as a function of mass of groups and
clusters M_cl and show that E_agn is proportional to M_cl^alpha with alpha~1.5.
We demonstrate that the entropy measurements, in conjunction with our model,
can be translated into constraints on the cluster--black hole mass relation.
The inferred relation is nonlinear and has the form M_bh\propto M_cl^alpha.
This scaling is an analog and extension of a similar relation between the black
hole mass and the galactic halo mass that holds on smaller scales. We show that
the central decrement of the CMB temperature is reduced due to the enhanced
entropy of the ICM, and that the decrement predicted from the plausible range
of energy input from the AGN is consistent with available data of SZ decrement.
We show that AGN heating, combined with the observational constraints on
entropy, leads to suppression of higher multipole moments in the angular power
spectrum and we find that this effect is stronger than previously thought.Comment: accepted for publication in The Astrophysical Journa
Combinatorial Hopf algebras in quantum field theory I
This manuscript stands at the interface between combinatorial Hopf algebra
theory and renormalization theory. Its plan is as follows: Section 1 is the
introduction, and contains as well an elementary invitation to the subject. The
rest of part I, comprising Sections 2-6, is devoted to the basics of Hopf
algebra theory and examples, in ascending level of complexity. Part II turns
around the all-important Faa di Bruno Hopf algebra. Section 7 contains a first,
direct approach to it. Section 8 gives applications of the Faa di Bruno algebra
to quantum field theory and Lagrange reversion. Section 9 rederives the related
Connes-Moscovici algebras. In Part III we turn to the Connes-Kreimer Hopf
algebras of Feynman graphs and, more generally, to incidence bialgebras. In
Section10 we describe the first. Then in Section11 we give a simple derivation
of (the properly combinatorial part of) Zimmermann's cancellation-free method,
in its original diagrammatic form. In Section 12 general incidence algebras are
introduced, and the Faa di Bruno bialgebras are described as incidence
bialgebras. In Section 13, deeper lore on Rota's incidence algebras allows us
to reinterpret Connes-Kreimer algebras in terms of distributive lattices. Next,
the general algebraic-combinatorial proof of the cancellation-free formula for
antipodes is ascertained; this is the heart of the paper. The structure results
for commutative Hopf algebras are found in Sections 14 and 15. An outlook
section very briefly reviews the coalgebraic aspects of quantization and the
Rota-Baxter map in renormalization.Comment: 94 pages, LaTeX figures, precisions made, typos corrected, more
references adde
Dynamics of intersecting brane systems -- Classification and their applications --
We present dynamical intersecting brane solutions in higher-dimensional
gravitational theory coupled to dilaton and several forms. Assuming the forms
of metric, form fields, and dilaton field, we give a complete classification of
dynamical intersecting brane solutions with/without M-waves and Kaluza-Klein
monopoles in eleven-dimensional supergravity. We apply these solutions to
cosmology and black holes. It is shown that these give FRW cosmological
solutions and in some cases Lorentz invariance is broken in our world. If we
regard the bulk space as our universe, we may interpret them as black holes in
the expanding universe. We also discuss lower-dimensional effective theories
and point out naive effective theories may give us some solutions which are
inconsistent with the higher-dimensional Einstein equations.Comment: 44 pages; v2: minor corrections, references adde
Comptonia peregrina (L.) J.M. Coult.
https://thekeep.eiu.edu/herbarium_specimens_byname/21520/thumbnail.jp
Comptonia peregrina (L.) J.M. Coult.
https://thekeep.eiu.edu/herbarium_specimens_byname/21520/thumbnail.jp
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