294 research outputs found
Soft gluon resummation for squark and gluino pair-production at hadron colliders
We report on the study of soft gluon effects in the production of squarks and
gluinos at hadron colliders. Close to production threshold, the emission of
soft gluon results in the appearence of large logarithmic corrections in the
theoretical expressions. In order to resum these corrections at
next-to-leading-logarithmic accuracy appropriate one-loop anomalous dimensions
have to be calculated. We present the calculation of the anomalous dimensions
for all production channels of squarks and gluinos and provide numerical
predictions for the Tevatron and the LHC.Comment: 6 pages, talk given at RADCOR 2009 - 9th International Symposium on
Radiative Corrections (Applications of Quantum Field Theory to Phenomenology)
October 25-30 2009, Ascona, Switzerlan
Luminous red galaxies in the Kilo Degree Survey: selection with broad-band photometry and weak lensing measurements
We use the overlap between multiband photometry of the Kilo-Degree Survey
(KiDS) and spectroscopic data based on the Sloan Digital Sky Survey (SDSS) and
Galaxy And Mass Assembly (GAMA) to infer the colour-magnitude relation of
red-sequence galaxies. We then use this inferred relation to select luminous
red galaxies (LRGs) in the redshift range of over the entire KiDS
Data Release 3 footprint. We construct two samples of galaxies with different
constant comoving densities and different luminosity thresholds. The selected
red galaxies have photometric redshifts with typical photo-z errors of
that are nearly uniform with respect to
observational systematics. This makes them an ideal set of galaxies for lensing
and clustering studies. As an example, we use the KiDS-450 cosmic shear
catalogue to measure the mean tangential shear signal around the selected LRGs.
We detect a significant weak lensing signal for lenses out to
Intrinsic alignments of galaxies in the Horizon-AGN cosmological hydrodynamical simulation
The intrinsic alignments of galaxies are recognised as a contaminant to weak
gravitational lensing measurements. In this work, we study the alignment of
galaxy shapes and spins at low redshift () in Horizon-AGN, an
adaptive-mesh-refinement hydrodynamical cosmological simulation box of 100
Mpc/h a side with AGN feedback implementation. We find that spheroidal galaxies
in the simulation show a tendency to be aligned radially towards over-densities
in the dark matter density field and other spheroidals. This trend is in
agreement with observations, but the amplitude of the signal depends strongly
on how shapes are measured and how galaxies are selected in the simulation.
Disc galaxies show a tendency to be oriented tangentially around spheroidals in
three-dimensions. While this signal seems suppressed in projection, this does
not guarantee that disc alignments can be safely ignored in future weak lensing
surveys. The shape alignments of luminous galaxies in Horizon-AGN are in
agreement with observations and other simulation works, but we find less
alignment for lower luminosity populations. We also characterize the
systematics of galaxy shapes in the simulation and show that they can be safely
neglected when measuring the correlation of the density field and galaxy
ellipticities.Comment: 20 pages, 23 figure
The Horizon-AGN simulation: evolution of galaxy properties over cosmic time
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We compare the predictions of Horizon-AGN, a hydro-dynamical cosmological simulation that uses an adaptive mesh refinement code, to observational data in the redshift range 0 < z < 6. We study the reproduction, by the simulation, of quantities that trace the aggregate stellar-mass growth of galaxies over cosmic time: luminosity and stellar-mass functions, the star formation main sequence, rest-frame UV-optical-near infrared colours and the cosmic star-formation history. We show that Horizon-AGN, which is not tuned to reproduce the local Universe, produces good overall agreement with these quantities, from the present day to the epoch when the Universe was 5% of its current age. By comparison to Horizon-noAGN, a twin simulation without AGN feedback, we quantify how feedback from black holes is likely to help shape galaxy stellar-mass growth in the redshift range 0 < z < 6, particularly in the most massive galaxies. Our results demonstrate that Horizon-AGN successfully captures the evolutionary trends of observed galaxies over the lifetime of the Universe, making it an excellent tool for studying the processes that drive galaxy evolution and making predictions for the next generation of galaxy surveys.Peer reviewedFinal Published versio
The halo model as a versatile tool to predict intrinsic alignments
Intrinsic alignments (IAs) of galaxies are an important contaminant for
cosmic shear studies, but the modelling is complicated by the dependence of the
signal on the source galaxy sample. In this paper, we use the halo model
formalism to capture this diversity and examine its implications for Stage-III
and Stage-IV cosmic shear surveys. We account for the different IA signatures
at large and small scales, as well for the different contributions from
central/satellite and red/blue galaxies, and we use realistic mocks to account
for the characteristics of the galaxy populations as a function of redshift. We
inform our model using the most recent observational findings: we include a
luminosity dependence at both large and small scales and a radial dependence of
the signal within the halo. We predict the impact of the total IA signal on the
lensing angular power spectra, including the current uncertainties from the IA
best-fits to illustrate the range of possible impact on the lensing signal: the
lack of constraints for fainter galaxies is the main source of uncertainty for
our predictions of the IA signal. We investigate how well effective models with
limited degrees of freedom can account for the complexity of the IA signal.
Although these lead to negligible biases for Stage-III surveys, we find that,
for Stage-IV surveys, it is essential to at least include an additional
parameter to capture the redshift dependence.Comment: 21 pages, 15 figure, accepted for publication in MNRA
Consistent cosmic shear in the face of systematics: a B-mode analysis of KiDS-450, DES-SV and CFHTLenS
We analyse three public cosmic shear surveys; the Kilo-Degree Survey (KiDS-450), the Dark Energy Survey (DES-SV) and the Canada France Hawaii Telescope Lensing Survey (CFHTLenS). Adopting the “COSEBIs” statistic to cleanly and completely separate the lensing E-modes from the non-lensing B-modes, we detect B-modes in KiDS-450 and CFHTLenS at the level of ∼2.7σ. For DES-SV we detect B-modes at the level of 2.8σ in a non-tomographic analysis, increasing to a 5.5σB-mode detection in a tomographic analysis. In order to understand the origin of these detected B-modes we measure the B-mode signature of a range of different simulated systematics including PSF leakage, random but correlated PSF modelling errors, camera-based additive shear bias and photometric redshift selection bias. We show that any correlation between photometric-noise and the relative orientation of the galaxy to the point-spread-function leads to an ellipticity selection bias in tomographic analyses. This work therefore introduces a new systematic for future lensing surveys to consider. We find that the B-modes in DES-SV appear similar to a superposition of the B-mode signatures from all of the systematics simulated. The KiDS-450 and CFHTLenS B-mode measurements show features that are consistent with a repeating additive shear bias
KiDS+GAMA:Intrinsic alignment model constraints for current and future weak lensing cosmology
We directly constrain the non-linear alignment (NLA) model of intrinsic
galaxy alignments, analysing the most representative and complete flux-limited
sample of spectroscopic galaxies available for cosmic shear surveys. We measure
the projected galaxy position-intrinsic shear correlations and the projected
galaxy clustering signal using high-resolution imaging from the Kilo Degree
Survey (KiDS) overlapping with the GAMA spectroscopic survey, and data from the
Sloan Digital Sky Survey. Separating samples by colour, we make no significant
detection of blue galaxy alignments, constraining the blue galaxy NLA amplitude
to be consistent with zero.
We make robust detections () for red galaxies, with
, corresponding to a net
radial alignment with the galaxy density field, and we find no evidence for any
scaling of alignments with galaxy luminosity. We provide informative priors for
current and future weak lensing surveys, an improvement over de facto wide
priors that allow for unrealistic levels of intrinsic alignment contamination.
For a colour-split cosmic shear analysis of the final KiDS survey area, we
forecast that our priors will improve the constraining power on and the
dark energy equation of state , by up to and ,
respectively. Our results indicate, however, that the modelling of
red/blue-split galaxy alignments may be insufficient to describe samples with
variable central/satellite galaxy fractions.Comment: 27 pages (incl. 7 appendix pages), 10 figures, accepted by A&
An aligned-spin neutron-star--black-hole waveform model based on the effective-one-body approach and numerical-relativity simulations
After the discovery of gravitational waves from binary black holes (BBHs) and
binary neutron stars (BNSs) with the LIGO and Virgo detectors,
neutron-star--black-holes (NSBHs) are the natural next class of binary systems
to be observed. In this work, we develop a waveform model for aligned-spin
neutron-star--black-holes (NSBHs) combining a binary black-hole baseline
waveform (available in the effective-one-body approach) with a phenomenological
description of tidal effects (extracted from numerical-relativity simulations),
and correcting the amplitude during the late inspiral, merger and ringdown to
account for the NS's tidal disruption. In particular, we calibrate the
amplitude corrections using NSBH waveforms obtained with the
numerical-relativity spectral Einstein code (SpEC) and the SACRA code. Based on
the simulations used, and on checking that sensible waveforms are produced, we
recommend our model to be employed with NS's mass in the range ,
tidal deformability 0\mbox{-}5000, and (dimensionless) BH's spin magnitude up
to . We also validate our model against two new, highly accurate NSBH
waveforms with BH's spin 0.9 and mass ratios 3 and 4, characterized by tidal
disruption, produced with SpEC, and find very good agreement. Furthermore, we
compute the unfaithfulness between waveforms from NSBH, BBH, and BNS systems,
finding that it will be challenging for the advanced LIGO-Virgo--detector
network at design sensitivity to distinguish different source classes. We
perform a Bayesian parameter-estimation analysis on a synthetic
numerical-relativity signal in zero noise to study parameter biases. Finally,
we reanalyze GW170817, with the hypothesis that it is a NSBH. We do not find
evidence to distinguish the BNS and NSBH hypotheses, however the posterior for
the mass ratio is shifted to less equal masses under the NSBH hypothesis.Comment: 18 pages, 10 Figure
Organised Randoms: learning and correcting for systematic galaxy clustering patterns in KiDS using self-organising maps
We present a new method for the mitigation of observational systematic
effects in angular galaxy clustering via corrective random galaxy catalogues.
Real and synthetic galaxy data, from the Kilo Degree Survey's (KiDS)
4 Data Release (KiDS-) and the Full-sky Lognormal
Astro-fields Simulation Kit (FLASK) package respectively, are used to train
self-organising maps (SOMs) to learn the multivariate relationships between
observed galaxy number density and up to six systematic-tracer variables,
including seeing, Galactic dust extinction, and Galactic stellar density. We
then create `organised' randoms, i.e. random galaxy catalogues with spatially
variable number densities, mimicking the learnt systematic density modes in the
data. Using realistically biased mock data, we show that these organised
randoms consistently subtract spurious density modes from the two-point angular
correlation function , correcting biases of up to in
the mean clustering amplitude to as low as , over a high
signal-to-noise angular range of 7-100 arcmin. Their performance is also
validated for angular clustering cross-correlations in a bright, flux-limited
subset of KiDS-, comparing against an analogous sample constructed from
highly-complete spectroscopic redshift data. Each organised random catalogue
object is a `clone' carrying the properties of a real galaxy, and is
distributed throughout the survey footprint according to the parent galaxy's
position in systematics-space. Thus, sub-sample randoms are readily derived
from a single master random catalogue via the same selection as applied to the
real galaxies. Our method is expected to improve in performance with increased
survey area, galaxy number density, and systematic contamination, making
organised randoms extremely promising for current and future clustering
analyses of faint samples.Comment: 18 pages (6 appendix pages), 12 figures (8 appendix figures),
submitted to A&
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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