143,093 research outputs found
Jet Substructure at the Tevatron and LHC: New results, new tools, new benchmarks
In this report we review recent theoretical progress and the latest
experimental results in jet substructure from the Tevatron and the LHC. We
review the status of and outlook for calculation and simulation tools for
studying jet substructure. Following up on the report of the Boost 2010
workshop, we present a new set of benchmark comparisons of substructure
techniques, focusing on the set of variables and grooming methods that are
collectively known as "top taggers". To facilitate further exploration, we have
attempted to collect, harmonise, and publish software implementations of these
techniques.Comment: 53 pages, 17 figures. L. Asquith, S. Rappoccio, C. K. Vermilion,
editors; v2: minor edits from journal revision
Alpha, Betti and the Megaparsec Universe: on the Topology of the Cosmic Web
We study the topology of the Megaparsec Cosmic Web in terms of the
scale-dependent Betti numbers, which formalize the topological information
content of the cosmic mass distribution. While the Betti numbers do not fully
quantify topology, they extend the information beyond conventional cosmological
studies of topology in terms of genus and Euler characteristic. The richer
information content of Betti numbers goes along the availability of fast
algorithms to compute them.
For continuous density fields, we determine the scale-dependence of Betti
numbers by invoking the cosmologically familiar filtration of sublevel or
superlevel sets defined by density thresholds. For the discrete galaxy
distribution, however, the analysis is based on the alpha shapes of the
particles. These simplicial complexes constitute an ordered sequence of nested
subsets of the Delaunay tessellation, a filtration defined by the scale
parameter, . As they are homotopy equivalent to the sublevel sets of
the distance field, they are an excellent tool for assessing the topological
structure of a discrete point distribution. In order to develop an intuitive
understanding for the behavior of Betti numbers as a function of , and
their relation to the morphological patterns in the Cosmic Web, we first study
them within the context of simple heuristic Voronoi clustering models.
Subsequently, we address the topology of structures emerging in the standard
LCDM scenario and in cosmological scenarios with alternative dark energy
content. The evolution and scale-dependence of the Betti numbers is shown to
reflect the hierarchical evolution of the Cosmic Web and yields a promising
measure of cosmological parameters. We also discuss the expected Betti numbers
as a function of the density threshold for superlevel sets of a Gaussian random
field.Comment: 42 pages, 14 figure
The Third Gravitational Lensing Accuracy Testing (GREAT3) Challenge Handbook
The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is the third
in a series of image analysis challenges, with a goal of testing and
facilitating the development of methods for analyzing astronomical images that
will be used to measure weak gravitational lensing. This measurement requires
extremely precise estimation of very small galaxy shape distortions, in the
presence of far larger intrinsic galaxy shapes and distortions due to the
blurring kernel caused by the atmosphere, telescope optics, and instrumental
effects. The GREAT3 challenge is posed to the astronomy, machine learning, and
statistics communities, and includes tests of three specific effects that are
of immediate relevance to upcoming weak lensing surveys, two of which have
never been tested in a community challenge before. These effects include
realistically complex galaxy models based on high-resolution imaging from
space; spatially varying, physically-motivated blurring kernel; and combination
of multiple different exposures. To facilitate entry by people new to the
field, and for use as a diagnostic tool, the simulation software for the
challenge is publicly available, though the exact parameters used for the
challenge are blinded. Sample scripts to analyze the challenge data using
existing methods will also be provided. See http://great3challenge.info and
http://great3.projects.phys.ucl.ac.uk/leaderboard/ for more information.Comment: 30 pages, 13 figures, submitted for publication, with minor edits
(v2) to address comments from the anonymous referee. Simulated data are
available for download and participants can find more information at
http://great3.projects.phys.ucl.ac.uk/leaderboard
Shape anisotropy of polymers in disordered environment
We study the influence of structural obstacles in a disordered environment on
the size and shape characteristics of long flexible polymer macromolecules. We
use the model of self-avoiding random walks on diluted regular lattices at the
percolation threshold in space dimensions d=2, 3. Applying the Pruned-Enriched
Rosenbluth Method (PERM), we numerically estimate rotationally invariant
universal quantities such as the averaged asphericity A_d and prolateness S of
polymer chain configurations. Our results quantitatively reveal the extent of
anisotropy of macromolecules due to the presence of structural defects.Comment: 8 page
Statistical properties of dark matter mini-haloes at z >= 15
Understanding the formation of the first objects in the universe critically
depends on knowing whether the properties of small dark matter structures at
high-redshift (z > 15) are different from their more massive lower-redshift
counterparts. To clarify this point, we performed a high-resolution N-body
simulation of a cosmological volume 1 Mpc/h comoving on a side, reaching the
highest mass resolution to date in this regime. We make precision measurements
of various physical properties that characterize dark matter haloes (such as
the virial ratio, spin parameter, shape, and formation times, etc.) for the
high-redshift (z > 15) dark matter mini-haloes we find in our simulation, and
compare them to literature results and a moderate-resolution comparison run
within a cube of side-length 100 Mpc/h. We find that dark matter haloes at
high-redshift have a log-normal distribution of the dimensionless spin
parameter centered around {\lambda} 0.03, similar to their more massive
counterparts. They tend to have a small ratio of the length of the shortest
axis to the longest axis (sphericity), and are highly prolate. In fact, haloes
of given mass that formed recently are the least spherical, have the highest
virial ratios, and have the highest spins. Interestingly, the formation times
of our mini-halos depend only very weakly on mass, in contrast to more massive
objects. This is expected from the slope of the linear power spectrum of
density perturbations at this scale, but despite this difference, dark matter
structures at high-redshift share many properties with their much more massive
counterparts observed at later times.Comment: 17 pages. Accepted for publication in MNRA
Detailed Decomposition of Galaxy Images. II. Beyond Axisymmetric Models
We present a two-dimensional (2-D) fitting algorithm (GALFIT, Version 3) with
new capabilities to study the structural components of galaxies and other
astronomical objects in digital images. Our technique improves on previous 2-D
fitting algorithms by allowing for irregular, curved, logarithmic and power-law
spirals, ring and truncated shapes in otherwise traditional parametric
functions like the Sersic, Moffat, King, Ferrer, etc., profiles. One can mix
and match these new shape features freely, with or without constraints, apply
them to an arbitrary number of model components and of numerous profile types,
so as to produce realistic-looking galaxy model images. Yet, despite the
potential for extreme complexity, the meaning of the key parameters like the
Sersic index, effective radius or luminosity remain intuitive and essentially
unchanged. The new features have an interesting potential for use to quantify
the degree of asymmetry of galaxies, to quantify low surface brightness tidal
features beneath and beyond luminous galaxies, to allow more realistic
decompositions of galaxy subcomponents in the presence of strong rings and
spiral arms, and to enable ways to gauge the uncertainties when decomposing
galaxy subcomponents. We illustrate these new features by way of several case
studies that display various levels of complexity.Comment: 41 pages, 22 figures, AJ accepted. Minor changes. Full resolution
version of this paper is available at:
http://users.obs.carnegiescience.edu/peng/work/galfit/galfit3.pd
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