143 research outputs found
Spatial curvature endgame: Reaching the limit of curvature determination
Current constraints on spatial curvature show that it is dynamically
negligible: (95% CL). Neglecting
it as a cosmological parameter would be premature however, as more stringent
constraints on at around the level would offer
valuable tests of eternal inflation models and probe novel large-scale
structure phenomena. This precision also represents the "curvature floor",
beyond which constraints cannot be meaningfully improved due to the cosmic
variance of horizon-scale perturbations. In this paper, we discuss what future
experiments will need to do in order to measure spatial curvature to this
maximum accuracy. Our conservative forecasts show that the curvature floor is
unreachable - by an order of magnitude - even with Stage IV experiments, unless
strong assumptions are made about dark energy evolution and the CDM
parameter values. We also discuss some of the novel problems that arise when
attempting to constrain a global cosmological parameter like
with such high precision. Measuring curvature down to this level would be an
important validation of systematics characterisation in high-precision
cosmological analyses.Comment: 9 pages, 1 figure. Updated to match version published in Phys. Rev.
Exploring degeneracies in modified gravity with weak lensing
By considering linear-order departures from general relativity, we compute a
novel expression for the weak lensing convergence power spectrum under
alternative theories of gravity. This comprises an integral over a 'kernel' of
general relativistic quantities multiplied by a theory-dependent 'source' term.
The clear separation between theory-independent and -dependent terms allows for
an explicit understanding of each physical effect introduced by altering the
theory of gravity. We take advantage of this to explore the degeneracies
between gravitational parameters in weak lensing observations.Comment: 17 pages, 7 figures. v2: Minor changes to match version accepted by
PR
Modified Gravity and Dark Energy models Beyond CDM Testable by LSST
One of the main science goals of the Large Synoptic Survey Telescope (LSST)
is to uncover the nature of cosmic acceleration. In the base analysis, possible
deviations from the Lambda-Cold-Dark-Matter (CDM) background evolution
will be probed by fitting a CDM model, which allows for a
redshift-dependent dark energy equation of state with , within general
relativity (GR). A rich array of other phenomena can arise due to deviations
from the standard CDM+GR model though, including modifications to the
growth rate of structure and lensing, and novel screening effects on non-linear
scales. Concrete physical models are needed to provide consistent predictions
for these (potentially small) effects, to give us the best chance of detecting
them and separating them from astrophysical systematics. A complex plethora of
possible models has been constructed over the past few decades, with none
emerging as a particular favorite. This document prioritizes a subset of these
models along with rationales for further study and inclusion into the LSST Dark
Energy Science Collaboration (DESC) data analysis pipelines, based on their
observational viability, theoretical plausibility, and level of theoretical
development. We provide references and theoretical expressions to aid the
integration of these models into DESC software and simulations, and give
justifications for why other models were not prioritized. While DESC efforts
are free to pursue other models, we provide here guidelines on which theories
appear to have higher priority for collaboration efforts due to their perceived
promise and greater instructional value.Comment: 61 pages. Some acknowledgments and references added. This is
version-1.1 of an internal collaboration document of LSST-DESC that is being
made public and is not planned for submission to a journa
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Narrative skills in adolescents with a history of SLI in relation to non-verbal IQ scores
There is a debate about whether the language of children with primary language disorders and normal cognitive levels is qualitatively different from those with language impairments who have low or borderline non-verbal IQ (NVIQ). As children reach adolescence, this distinction may be even harder to ascertain, especially in naturalistic settings. Narrative may provide a useful, ecologically valid way in which to assess the language ability of adolescents with specific language impairment (SLI) who have intact or lowered NVIQ and to determine whether there is any discernable difference in every day language. Nineteen adolescents with a history of SLI completed two narrative tasks: a story telling condition and a conversational condition. Just under half the group (n = 8) had non-verbal IQs of 85. The remaining 11 had NVIQs in the normal range or above. Four areas of narrative (productivity, syntax, cohesion and performance) were assessed. There were no differences between the groups on standardized tests of language. However, the group with low NVIQ were poorer on most aspects of narrative, suggesting that cognitive level is important, even when language is the primary disorder. The groups showed similar patterns of differences between story telling and conversational narrative. It was concluded that adolescents with a history of SLI and poor cognitive levels have poorer narrative skills than those with normal range NVIQ even though these may not be detected by standardized assessment. Their difficulties present as qualitatively similar to those with normal range NVIQ and narratives appear impoverished rather than inaccurate
An Empirical Model For Intrinsic Alignments: Insights From Cosmological Simulations
We extend current models of the halo occupation distribution (HOD) to include
a flexible, empirical framework for the forward modeling of the intrinsic
alignment (IA) of galaxies. A primary goal of this work is to produce mock
galaxy catalogs for the purpose of validating existing models and methods for
the mitigation of IA in weak lensing measurements. This technique can also be
used to produce new, simulation-based predictions for IA and galaxy clustering.
Our model is probabilistically formulated, and rests upon the assumption that
the orientations of galaxies exhibit a correlation with their host dark matter
(sub)halo orientation or with their position within the halo. We examine the
necessary components and phenomenology of such a model by considering the
alignments between (sub)halos in a cosmological dark matter only simulation. We
then validate this model for a realistic galaxy population in a set of
simulations in the Illustris-TNG suite. We create an HOD mock with
Illustris-like correlations using our method, constraining the associated IA
model parameters, with the between our model's correlations
and those of Illustris matching as closely as 1.4 and 1.1 for
orientation--position and orientation--orientation correlation functions,
respectively. By modeling the misalignment between galaxies and their host
halo, we show that the 3-dimensional two-point position and orientation
correlation functions of simulated (sub)halos and galaxies can be accurately
reproduced from quasi-linear scales down to . We also find
evidence for environmental influence on IA within a halo. Our
publicly-available software provides a key component enabling efficient
determination of Bayesian posteriors on IA model parameters using observational
measurements of galaxy-orientation correlation functions in the highly
nonlinear regime.Comment: 17 pages, 12 figures, 3 tables, for submission to The Open Journal of
Astrophysics, code available at https://github.com/astropy/halotool
Wide-field Multi-object Spectroscopy to Enhance Dark Energy Science from LSST
LSST will open new vistas for cosmology in the next decade, but it cannot
reach its full potential without data from other telescopes. Cosmological
constraints can be greatly enhanced using wide-field ( deg total
survey area), highly-multiplexed optical and near-infrared multi-object
spectroscopy (MOS) on 4-15m telescopes. This could come in the form of
suitably-designed large surveys and/or community access to add new targets to
existing projects. First, photometric redshifts can be calibrated with high
precision using cross-correlations of photometric samples against spectroscopic
samples at that span thousands of sq. deg. Cross-correlations of
faint LSST objects and lensing maps with these spectroscopic samples can also
improve weak lensing cosmology by constraining intrinsic alignment systematics,
and will also provide new tests of modified gravity theories. Large samples of
LSST strong lens systems and supernovae can be studied most efficiently by
piggybacking on spectroscopic surveys covering as much of the LSST
extragalactic footprint as possible (up to square degrees).
Finally, redshifts can be measured efficiently for a high fraction of the
supernovae in the LSST Deep Drilling Fields (DDFs) by targeting their hosts
with wide-field spectrographs. Targeting distant galaxies, supernovae, and
strong lens systems over wide areas in extended surveys with (e.g.) DESI or MSE
in the northern portion of the LSST footprint or 4MOST in the south could
realize many of these gains; DESI, 4MOST, Subaru/PFS, or MSE would all be
well-suited for DDF surveys. The most efficient solution would be a new
wide-field, highly-multiplexed spectroscopic instrument in the southern
hemisphere with m aperture. In two companion white papers we present gains
from deep, small-area MOS and from single-target imaging and spectroscopy.Comment: Submitted to the call for Astro2020 science white papers; tables with
estimates of telescope time needed for a supernova host survey can be seen at
http://d-scholarship.pitt.edu/id/eprint/3604
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