424 research outputs found
Some Correlation Functions of Minimal Superconformal Models Coupled to Supergravity
We compute general three-point functions of minimal superconformal models
coupled to supergravity in the Neveu-Schwarz sector for spherical topology thus
extending to the superconformal case the results of Goulian and Li and of
Dotsenko.Comment: 15 page
An integrable spin chain for the SL(2,R)/U(1) black hole sigma model
We introduce a spin chain based on finite-dimensional spin-1/2 SU(2)
representations but with a non-hermitian `Hamiltonian' and show, using mostly
analytical techniques, that it is described at low energies by the SL(2,R)/U(1)
Euclidian black hole Conformal Field Theory. This identification goes beyond
the appearance of a non-compact spectrum: we are also able to determine the
density of states, and show that it agrees with the formulas in [J. Math. Phys.
42, 2961 (2001)] and [JHEP 04, 014 (2002)], hence providing a direct `physical
measurement' of the associated reflection amplitude.Comment: 6 pages, 3 figures, in RevTeX. Corrected some typo
An integrable modification of the critical Chalker-Coddington network model
We consider the Chalker-Coddington network model for the Integer Quantum Hall
Effect, and examine the possibility of solving it exactly. In the
supersymmetric path integral framework, we introduce a truncation procedure,
leading to a series of well-defined two-dimensional loop models, with two loop
flavours. In the phase diagram of the first-order truncated model, we identify
four integrable branches related to the dilute Birman-Wenzl-Murakami
braid-monoid algebra, and parameterised by the loop fugacity . In the
continuum limit, two of these branches (1,2) are described by a pair of
decoupled copies of a Coulomb-Gas theory, whereas the other two branches (3,4)
couple the two loop flavours, and relate to an Wess-Zumino-Witten (WZW) coset model for the particular values where is a positive integer. The truncated
Chalker-Coddington model is the point of branch 4. By numerical
diagonalisation, we find that its universality class is neither an analytic
continuation of the WZW coset, nor the universality class of the original
Chalker-Coddington model. It constitutes rather an integrable, critical
approximation to the latter.Comment: 34 pages, 18 figures, 3 appendice
An algebraic approach to logarithmic conformal field theory
A comprehensive introduction to logarithmic conformal field theory, using an
algebraic point of view, is given. A number of examples are explained in
detail, including the c=-2 triplet theory and the k=-4/3 affine su(2) theory.
We also give some brief introduction to the work of Zhu.Comment: 55 pages, LaTeX, 2 figures; notes of lectures delivered at the school
on Logarithmic Conformal Field Theory and its Applications, IPM Tehran,
September 200
Herschel observations of embedded protostellar clusters in the Rosette Molecular Cloud
The Herschel OB young stellar objects survey (HOBYS) has observed the Rosette
molecular cloud, providing an unprecedented view of its star formation
activity. These new far-infrared data reveal a population of compact young
stellar objects whose physical properties we aim to characterise. We compiled a
sample of protostars and their spectral energy distributions that covers the
near-infrared to submillimetre wavelength range. These were used to constrain
key properties in the protostellar evolution, bolometric luminosity, and
envelope mass and to build an evolutionary diagram. Several clusters are
distinguished including the cloud centre, the embedded clusters in the vicinity
of luminous infrared sources, and the interaction region. The analysed
protostellar population in Rosette ranges from 0.1 to about 15 Msun with
luminosities between 1 and 150 Lsun, which extends the evolutionary diagram
from low-mass protostars into the high-mass regime. Some sources lack
counterparts at near- to mid-infrared wavelengths, indicating extreme youth.
The central cluster and the Phelps & Lada 7 cluster appear less evolved than
the remainder of the analysed protostellar population. For the central cluster,
we find indications that about 25% of the protostars classified as Class I from
near- to mid-infrared data are actually candidate Class 0 objects. As a
showcase for protostellar evolution, we analysed four protostars of low- to
intermediate-mass in a single dense core, and they represent different
evolutionary stages from Class 0 to Class I. Their mid- to far-infrared
spectral slopes flatten towards the Class I stage, and the 160 to 70um flux
ratio is greatest for the presumed Class 0 source. This shows that the Herschel
observations characterise the earliest stages of protostellar evolution in
detail.Comment: Astronomy & Astrophysics letter, 6 pages, 4 figures, accepted for
publication in the Special Issue for Herschel first result
What determines the density structure of molecular clouds? A case study of Orion B with <i>Herschel</i>
A key parameter to the description of all star formation processes is the density structure of the gas. In this Letter, we make use of probability distribution functions (PDFs) of Herschel column density maps of Orion B, Aquila, and Polaris, obtained with the Herschel Gould Belt survey (HGBS). We aim to understand which physical processes influence the PDF shape, and with which signatures. The PDFs of Orion B (Aquila) show a lognormal distribution for low column densities until AV ~ 3 (6), and a power-law tail for high column densities, consistent with a ρα r-2 profile for the equivalent spherical density distribution. The PDF of Orion B is broadened by external compression due to the nearby OB stellar aggregates. The PDF of a quiescent subregion of the non-star-forming Polaris cloud is nearly lognormal, indicating that supersonic turbulence governs the density distribution. But we also observe a deviation from the lognormal shape at AV > 1 for a subregion in Polaris that includes a prominent filament. We conclude that (1) the point where the PDF deviates from the lognormal form does not trace a universal AV -threshold for star formation, (2) statistical density fluctuations, intermittency, and magnetic fields can cause excess from the lognormal PDF at an early cloud formation stage, (3) core formation and/or global collapse of filaments and a non-isothermal gas distribution lead to a power-law tail, and (4) external compression broadens the column density PDF, consistent with numerical simulations
A multi-scale, multi-wavelength source extraction method: getsources
We present a multi-scale, multi-wavelength source extraction algorithm called
getsources. Although it has been designed primarily for use in the far-infrared
surveys of Galactic star-forming regions with Herschel, the method can be
applied to many other astronomical images. Instead of the traditional approach
of extracting sources in the observed images, the new method analyzes fine
spatial decompositions of original images across a wide range of scales and
across all wavebands. It cleans those single-scale images of noise and
background, and constructs wavelength-independent single-scale detection images
that preserve information in both spatial and wavelength dimensions. Sources
are detected in the combined detection images by following the evolution of
their segmentation masks across all spatial scales. Measurements of the source
properties are done in the original background-subtracted images at each
wavelength; the background is estimated by interpolation under the source
footprints and overlapping sources are deblended in an iterative procedure. In
addition to the main catalog of sources, various catalogs and images are
produced that aid scientific exploitation of the extraction results. We
illustrate the performance of getsources on Herschel images by extracting
sources in sub-fields of the Aquila and Rosette star-forming regions. The
source extraction code and validation images with a reference extraction
catalog are freely available.Comment: 31 pages, 27 figures, to be published in Astronomy & Astrophysic
The Aquila prestellar core population revealed by Herschel
The origin and possible universality of the stellar initial mass function
(IMF) is a major issue in astrophysics. One of the main objectives of the
Herschel Gould Belt Survey is to clarify the link between the prestellar core
mass function (CMF) and the IMF. We present and discuss the core mass function
derived from Herschel data for the large population of prestellar cores
discovered with SPIRE and PACS in the Aquila Rift cloud complex at d ~ 260 pc.
We detect a total of 541 starless cores in the entire ~11 deg^2 area of the
field imaged at 70-500 micron with SPIRE/PACS. Most of these cores appear to be
gravitationally bound, and thus prestellar in nature. Our Herschel results
confirm that the shape of the prestellar CMF resembles the stellar IMF, with
much higher quality statistics than earlier submillimeter continuum
ground-based surveys
Herschel Observations of a Potential Core Forming Clump: Perseus B1-E
We present continuum observations of the Perseus B1-E region from the
Herschel Gould Belt Survey. These Herschel data reveal a loose grouping of
substructures at 160 - 500 micron not seen in previous submillimetre
observations. We measure temperature and column density from these data and
select the nine densest and coolest substructures for follow-up spectral line
observations with the Green Bank Telescope. We find that the B1-E clump has a
mass of ~ 100 solar masses and appears to be gravitationally bound.
Furthermore, of the nine substructures examined here, one substructure (B1-E2)
appears to be itself bound. The substructures are typically less than a Jeans
length from their nearest neighbour and thus, may interact on a timescale of ~
1 Myr. We propose that B1-E may be forming a first generation of dense cores,
which could provide important constraints on the initial conditions of
prestellar core formation. Our results suggest that B1-E may be influenced by a
strong, localized magnetic field, but further observations are still required.Comment: 14 pages, 8 figures, published in A&A: Minor calibration correctio
Faces of matrix models
Partition functions of eigenvalue matrix models possess a number of very
different descriptions: as matrix integrals, as solutions to linear and
non-linear equations, as tau-functions of integrable hierarchies and as
special-geometry prepotentials, as result of the action of W-operators and of
various recursions on elementary input data, as gluing of certain elementary
building blocks. All this explains the central role of such matrix models in
modern mathematical physics: they provide the basic "special functions" to
express the answers and relations between them, and they serve as a dream model
of what one should try to achieve in any other field.Comment: 10 page
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