141 research outputs found
Scale Dependence of the Halo Bias in General Local-Type Non-Gaussian Models I: Analytical Predictions and Consistency Relations
We investigate the clustering of halos in cosmological models starting with
general local-type non-Gaussian primordial fluctuations. We employ multiple
Gaussian fields and add local-type non-Gaussian corrections at arbitrary order
to cover a class of models described by frequently-discussed f_nl, g_nl and
\tau_nl parameterization. We derive a general formula for the halo power
spectrum based on the peak-background split formalism. The resultant spectrum
is characterized by only two parameters responsible for the scale-dependent
bias at large scale arising from the primordial non-Gaussianities in addition
to the Gaussian bias factor. We introduce a new inequality for testing
non-Gaussianities originating from multi fields, which is directly accessible
from the observed power spectrum. We show that this inequality is a
generalization of the Suyama-Yamaguchi inequality between f_nl and \tau_nl to
the primordial non-Gaussianities at arbitrary order. We also show that the
amplitude of the scale-dependent bias is useful to distinguish the simplest
quadratic non-Gaussianities (i.e., f_nl-type) from higher-order ones (g_nl and
higher), if one measures it from multiple species of galaxies or clusters of
galaxies. We discuss the validity and limitations of our analytic results by
comparison with numerical simulations in an accompanying paper.Comment: 25 pages, 3 figures, typo corrected, Appendix C updated, submitted to
JCA
Constraining Scale-Dependent Non-Gaussianity with Future Large-Scale Structure and the CMB
We forecast combined future constraints from the cosmic microwave background
and large-scale structure on the models of primordial non-Gaussianity. We study
the generalized local model of non-Gaussianity, where the parameter f_NL is
promoted to a function of scale, and present the principal component analysis
applicable to an arbitrary form of f_NL(k). We emphasize the complementarity
between the CMB and LSS by using Planck, DES and BigBOSS surveys as examples,
forecast constraints on the power-law f_NL(k) model, and introduce the figure
of merit for measurements of scale-dependent non-Gaussianity.Comment: 28 pages, 8 figures, 2 tables; v2: references update
Local stochastic non-Gaussianity and N-body simulations
Large-scale clustering of highly biased tracers of large-scale structure has
emerged as one of the best observational probes of primordial non-Gaussianity
of the local type (i.e. f_{NL}^{local}). This type of non-Gaussianity can be
generated in multifield models of inflation such as the curvaton model.
Recently, Tseliakhovich, Hirata, and Slosar showed that the clustering
statistics depend qualitatively on the ratio of inflaton to curvaton power \xi
after reheating, a free parameter of the model. If \xi is significantly
different from zero, so that the inflaton makes a non-negligible contribution
to the primordial adiabatic curvature, then the peak-background split ansatz
predicts that the halo bias will be stochastic on large scales. In this paper,
we test this prediction in N-body simulations. We find that large-scale
stochasticity is generated, in qualitative agreement with the prediction, but
that the level of stochasticity is overpredicted by ~30%. Other predictions,
such as \xi independence of the halo bias, are confirmed by the simulations.
Surprisingly, even in the Gaussian case we do not find that halo model
predictions for stochasticity agree consistently with simulations, suggesting
that semi-analytic modeling of stochasticity is generally more difficult than
modeling halo bias.Comment: v3: minor changes matching published versio
The implications of Brexit for environmental law in Scotland
This report maps the possible implications of Brexit for environmental protection in Scotland, identifying core questions as well as solutions that may be adopted, with the objective of initiating a conversation about this complex subject matter. The report has been prepared as a joint endeavour by a group of environmental law experts based at Scottish Universities. Each section was drafted by a lead author, with inputs from the rest of the group. The paper is meant for a broad audience and intentionally uses a non-technical writing style. The paper is divided in two sections. The first section addresses cross-cutting questions affecting environmental governance after Brexit, focusing on the main Brexit scenarios and their trade, competition, and law enforcement implications. This analysis identifies a series of common challenges for nvironmental law in Scotland after Brexit, which relate to: âąLoss of scrutiny and enforcement powers associated with the operation of EU law and institutions; âąLoss of long-term policy horizon and of the stable regulatory framework provided by EU law; âąRepositioning of the UK and Scotland in international and regional environmental governance cooperation; and âąRestriction/loss of access to EU funds and programmes. The second section analyses specific questions likely to emerge in elected areas of environmental law, distinguishing between different types of EU environmental legislation and the related allocation of competences within the UK. The transposition of EU environmental law into domestic law takes place in different ways. Some pieces of EU environmental law have been transposed into UK/Scottish law and configure distinctively UK/Scottish solutions. After Brexit, retaining these pieces of legislation is going to be relatively straightforward. Other pieces of EU environmental law, conversely, heavily rely upon EU processes and institutions and will no longer be applicable in their present form after Brexit. On these matters, EU powers and competences will be repatriated, raising fundamental questions concerning the allocation of powers between the UKâs central and evolved administrations. Finally, EU membership has important implications concerning the UKâs implementation of international obligations in areas such as climate change law or air pollution. In these areas, EU law is often more ambitious than the underlying international obligations. Brexit will therefore confront the UK and devolved administrations with fundamental choices regarding how to continue to comply with international obligations, and maintain and enhance their current level of commitment and ambition over time
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
Spontaneous fluctuations in a magnetic Fe/Gd skyrmion lattice
Magnetic skyrmions are topological spin textures that exhibit classical or quantum quasiparticle behavior. A substantial amount of research has occurred in this field, both because of their unique electromagnetic properties and potential application for future nonvolatile memory storage applications, as well as fundamental questions on their topology and unique magnetic phases. Here, we investigate the fluctuation properties of a magnetic Fe/Gd skyrmion lattice, using short-pulsed x rays. We first measure spontaneous fluctuations of the skyrmion lattice phase and find an inherent, collective mode showing an underdamped oscillation with a relaxation of a couple of nanoseconds. Further observations track the response towards the continuous phase transition and a critical-like slowing down of fluctuations is observed well before the critical point. These results suggest that the skyrmion lattice phase never fully freezes into a static crystal. This constant state of fluctuation indicates that the physics of topological magnetic phases may have more in common with high-temperature superconductors with disorder
Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets
The spins of ten stellar black holes have been measured using the
continuum-fitting method. These black holes are located in two distinct classes
of X-ray binary systems, one that is persistently X-ray bright and another that
is transient. Both the persistent and transient black holes remain for long
periods in a state where their spectra are dominated by a thermal accretion
disk component. The spin of a black hole of known mass and distance can be
measured by fitting this thermal continuum spectrum to the thin-disk model of
Novikov and Thorne; the key fit parameter is the radius of the inner edge of
the black hole's accretion disk. Strong observational and theoretical evidence
links the inner-disk radius to the radius of the innermost stable circular
orbit, which is trivially related to the dimensionless spin parameter a_* of
the black hole (|a_*| < 1). The ten spins that have so far been measured by
this continuum-fitting method range widely from a_* \approx 0 to a_* > 0.95.
The robustness of the method is demonstrated by the dozens or hundreds of
independent and consistent measurements of spin that have been obtained for
several black holes, and through careful consideration of many sources of
systematic error. Among the results discussed is a dichotomy between the
transient and persistent black holes; the latter have higher spins and larger
masses. Also discussed is recently discovered evidence in the transient sources
for a correlation between the power of ballistic jets and black hole spin.Comment: 30 pages. Accepted for publication in Space Science Reviews. Also to
appear in hard cover in the Space Sciences Series of ISSI "The Physics of
Accretion onto Black Holes" (Springer Publisher). Changes to Sections 5.2,
6.1 and 7.4. Section 7.4 responds to Russell et al. 2013 (MNRAS, 431, 405)
who find no evidence for a correlation between the power of ballistic jets
and black hole spi
Tackling transition:the value of peer mentoring
This paper is aimed at those interested in the promotion of student retention in higher education; particularly those with an interest in peer mentoring as a means of student support. It critically discusses the results of an exploratory study analysing the perceptions of peer mentors and mentees within five universities in the United Kingdom. The aim of the study was to analyse how student peer mentoring can aid transition into university by focusing specifically on how senior students can support their junior counterparts in their first year at university. The paper discusses the results of a survey which was completed by 329 student peer mentors and mentees. Focusing on the benefits and outcomes of participation in Mentoring Programmes, the survey was distinctive in that it asked mentors and mentees similar questions. From a theoretical perspective, the paper contributes to debates about peer support in higher education showing that participation in such programmes can have positive outcomes from both social and pedagogic perspectives. Practically speaking, the results have important implications for Higher Education Institutions as the research highlights the importance of putting into place formally structured Peer Mentoring Programmes which facilitate student support at a time when new students are most at risk of âdropping outâ
Zinc Supplements and Bone Health: The Role of the RANKL-RANK Axis as a Therapeutic Target
Background: To this day, empirical data suggests that zinc has important roles in matrix synthesis, bone turnover, and mineralization and its beneficial effects on bone could be mediated through different mechanisms. The influence of zinc on bone turnover could be facilitated via regulating RANKL/RANK/OPG pathway in bone tissue. Therefore, the aim of the study was to conduct a review to investigate the possible effect of the zinc mediated bone remodeling via RANKL/RANK/OPG pathway. Methods: A comprehensive systematic search was performed in MEDLINE/PubMed, Cochrane Library, SCOPUS, and Google Scholar to explore the studies investigating the effect of zinc as a bone remodeling factor via RANKL/RANK/OPG pathway regulation. Subsequently, the details of the pathway and the impact of zinc supplements on RANKL/RANK/OPG pathway regulation were discussed. Results: The pathway could play an important role in bone remodeling and any imbalance between RANKL/RANK/OPG components could lead to extreme bone resorption. Although the outcomes of some studies are equivocal, it is evident that zinc possesses protective properties against bone loss by regulating the RANKL/RANK/OPG pathway. There are several experiments where zinc supplementation resulted in upregulation of OPG expression or decreases RANKL level. However, the results of some studies oppose this. Conclusion: It is likely that sufficient zinc intake will elicit positive effects on bone health by RANKL/RANK/OPG regulation. Although the outcomes of a few studies are equivocal, it seems that zinc can exert the protective properties against bone loss by suppressing osteoclastogenesis via downregulation of RANKL/RANK. Additionally, there are several experiments where zinc supplementation resulted in upregulation of OPG expression. However, the results of limited studies oppose this. Therefore, aside from the positive role zinc possesses in preserving bone mass, further effects of zinc in RANKL/RANK/OPG system requires further animal/human studies. Ă© 2019 Elsevier Gmb
STRIDER (Sildenafil TheRapy in dismal prognosis early onset fetal growth restriction): An international consortium of randomised placebo-controlled trials
Background: Severe, early-onset fetal growth restriction due to placental insufficiency is associated with a high risk of perinatal mortality and morbidity with long-lasting sequelae. Placental insufficiency is the result of abnormal formation and function of the placenta with inadequate remodelling of the maternal spiral arteries. There is currently no effective therapy available. Some evidence suggests sildenafil citrate may improve uteroplacental blood flow, fetal growth, and meaningful infant outcomes. The objective of the Sildenafil TheRapy In Dismal prognosis Early onset fetal growth Restriction (STRIDER) collaboration is to evaluate the effectiveness of sildenafil versus placebo in achieving healthy perinatal survival through the conduct of randomised clinical trials and systematic review including individual patient data meta-analysis. Methods: Five national/bi-national multicentre randomised placebo-controlled trials have been launched. Women with a singleton pregnancy between 18 and 30 weeks with severe fetal growth restriction of likely placental origin, and where the likelihood of perinatal death/severe morbidity is estimated to be significant are included. Participants will receive either sildenafil 25 mg or matching placebo tablets orally three times daily from recruitment to 32 weeks gestation. Discussion: The STRIDER trials were conceived and designed through international collaboration. Although the individual trials have different primary outcomes for reasons of sample size and feasibility, all trials will collect a standard set of outcomes including survival without severe neonatal morbidity at time of hospital discharge. This is a summary of all the STRIDER trial protocols and provides an example of a prospectively planned international clinical research collaboration. All five individual trials will contribute to a pre-planned systematic review of the topic including individual patient data meta-analysis
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