134 research outputs found
A Small-Scale Modification to the Lensing Kernel
Calculations of the Cosmic Microwave Background lensing power implemented
into the standard cosmological codes such as CAMB and CLASS usually treat the
surface of last scatter as an infinitely thin screen. However, since the CMB
anisotropies are smoothed out on scales smaller than the diffusion length due
to the effect of Silk damping, the photons which carry information about the
small-scale density distribution come from slightly earlier times than the
standard recombination time. The dominant effect is the scale dependence of the
mean redshift associated with the fluctuations during recombination. We find
that fluctuations at come from a characteristic
redshift of , while fluctuations at
come from a characteristic redshift of . We then estimate the
corrections to the lensing kernel and the related power spectra due to this
effect. We conclude that neglecting it would result in a deviation from the
true value of the lensing kernel at the half percent level at small CMB scales.
For an all-sky, noise-free experiment, this corresponds to a
shift in the observed temperature power spectrum on small scales ().Comment: 5 pages, 5 figure
Neutrino masses and beyond-CDM cosmology with LSST and future CMB experiments
Cosmological measurements over the next decade will enable us to shed light
on the content and evolution of the Universe. Complementary measurements of the
Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations are expected
to allow an indirect determination of the sum of neutrino masses, within the
framework of the flat CDM model. However, possible deviations from
CDM such as a non-zero cosmological curvature or a dark energy
equation of state with would leave similar imprints on the expansion
rate of the Universe and clustering of matter. We show how future CMB
measurements can be combined with late-time measurements of galaxy clustering
and cosmic shear from the Large Synoptic Survey Telescope to alleviate this
degeneracy. Together, they are projected to reduce the uncertainty on the
neutrino mass sum to 30 meV within this more general cosmological model.
Achieving a 3 measurement of the minimal 60 meV mass (or 4
assuming ) will require a five-fold improved measurement of the optical
depth to reionization, obtainable through a large-scale CMB polarization
measurement.Comment: 10 pages, 6 figures; v2, updated to PRD version, references adde
Simulated forecasts for primordial B-mode searches in ground-based experiments
Detecting the imprint of inflationary gravitational waves on the -mode
polarization of the Cosmic Microwave Background (CMB) is one of the main
science cases for current and next-generation CMB experiments. In this work we
explore some of the challenges that ground-based facilities will have to face
in order to carry out this measurement in the presence of Galactic foregrounds
and correlated atmospheric noise. We present forecasts for Stage-3 (S3) and
planned Stage-4 (S4) experiments based on the analysis of simulated sky maps
using a map-based Bayesian foreground cleaning method. Our results thus
consistently propagate the uncertainties on foreground parameters such as
spatially-varying spectral indices, as well as the bias on the measured
tensor-to-scalar ratio caused by an incorrect modelling of the foregrounds.
We find that S3 and S4-like experiments should be able to put constraints on
of the order and
respectively, assuming instrumental
systematic effects are under control. We further study deviations from the
fiducial foreground model, finding that, while the effects of a second
polarized dust component would be minimal on both S3 and S4, a 2\% polarized
anomalous dust emission (AME) component would be clearly detectable by Stage-4
experiments.Comment: 19 pages, 11 figure
Contamination of early-type galaxy alignments to galaxy lensing-CMB lensing cross-correlation
Galaxy shapes are subject to distortions due to the tidal field of the
Universe. The cross-correlation of galaxy lensing with the lensing of the
Cosmic Microwave Background (CMB) cannot easily be separated from the
cross-correlation of galaxy intrinsic shapes with CMB lensing. Previous work
suggested that the intrinsic alignment contamination can be of this
cross-spectrum for the CFHT Stripe 82 (CS82) and Atacama Cosmology Telescope
surveys. Here we re-examine these estimates using up-to-date observational
constraints of intrinsic alignments at a redshift more similar to that of CS82
galaxies. We find a contamination of the cross-spectrum from
red galaxies, with uncertainty due to uncertainties in the
redshift distribution of source galaxies and the modelling of the spectral
energy distribution. Blue galaxies are consistent with being unaligned, but
could contaminate the cross-spectrum by an additional within current
confidence levels. While our fiducial estimate of alignment
contamination is similar to previous work, our work suggests that the relevance
of alignments for CMB lensing-galaxy lensing cross-correlation remains largely
unconstrained. Little information is currently available about alignments at
. We consider the upper limiting case where all galaxies are
aligned with the same strength as low redshift luminous red galaxies, finding
as much as contamination.Comment: 11 pages, 3 figures, MNRAS submitte
Towards a cosmological neutrino mass detection
Future cosmological measurements should enable the sum of neutrino masses to
be determined indirectly through their effects on the expansion rate of the
Universe and the clustering of matter. We consider prospects for the
gravitationally lensed Cosmic Microwave Background anisotropies and Baryon
Acoustic Oscillations in the galaxy distribution, examining how the projected
uncertainty of meV on the neutrino mass sum (a 4 detection
of the minimal mass) might be reached over the next decade. The current
1 uncertainty of meV (Planck-2015+BAO-15) will be
improved by upcoming 'Stage-3' CMB experiments (S3+BAO-15: 44 meV), then
upcoming BAO measurements (S3+DESI: 22 meV), and planned next-generation 'Stage
4' CMB experiments (S4+DESI: 15-19 meV, depending on angular range). An
improved optical depth measurement is important: the projected neutrino mass
uncertainty increases to meV if S4 is limited to and combined
with current large-scale polarization data. Looking beyond CDM,
including curvature uncertainty increases the forecast mass error by
50% for S4+DESI, and more than doubles the error with a two-parameter dark
energy equation of state. Complementary low-redshift probes including galaxy
lensing will play a role in distinguishing between massive neutrinos and a
departure from a , flat geometry.Comment: Submitted to PRD. 15 pages, 10 figure
Lensing Simulation and Power Spectrum Estimation for High Resolution CMB Polarization Maps
We present efficient algorithms for CMB lensing simulation and power spectrum
es- timation for flat-sky CMB polarization maps. We build a pure B-mode
estimator to remedy E to B leakage due to partial sky coverage. We show that
our estimators are unbiased, and consistent with the projected errors. We
demonstrate our algorithm using simulated observations of small sky patches
with realistic noise and weights for upcoming CMB polarization experiments.Comment: 11 pages, 6 figure
Constraining Isocurvature Initial Conditions with WMAP 3-year data
We present constraints on the presence of isocurvature modes from the
temperature and polarization CMB spectrum data from the WMAP satellite alone,
and in combination with other datasets including SDSS galaxy survey and SNLS
supernovae. We find that the inclusion of polarization data allows the WMAP
data alone, as well as in combination with complementary observations, to place
improved limits on the contribution of CDM and neutrino density isocurvature
components individually. With general correlations, the upper limits on these
sub-dominant isocurvature components are reduced to ~60% of the first year WMAP
results, with specific limits depending on the type of fluctuations. If
multiple isocurvature components are allowed, however, we find that the data
still allow a majority of the initial power to come from isocurvature modes. As
well as providing general constraints we also consider their interpretation in
light of specific theoretical models like the curvaton and double inflation.Comment: 8 pages, 7 figures. Revised Sec 4 and Figs 3-4 post-publication to
correct an error for models with varying isocurvature spectral inde
Large-Scale Polarized Foreground Component Separation for Planck
We use Bayesian component estimation methods to examine the prospects for
large-scale polarized map and cosmological parameter estimation with simulated
Planck data assuming simplified white noise properties. The sky signal is
parametrized as the sum of the CMB, synchrotron emission, and thermal dust
emission. The synchrotron and dust components are modelled as power-laws, with
a spatially varying spectral index for synchrotron and a uniform index for
dust. Using the Gibbs sampling technique, we estimate the linear polarisation Q
and U posterior amplitudes of the CMB, synchrotron and dust maps as well as the
two spectral indices in ~4 degree pixels. We use the recovered CMB map and its
covariance in an exact pixel likelihood algorithm to estimate the optical depth
to reionization tau, the tensor-to-scalar ratio r, and to construct conditional
likelihood slices for the EE and BB spectra. Given our foreground model, we
find sigma(tau)~0.004 for tau=0.1, sigma(r)~0.03 for a model with r=0.1, and a
95% upper limit of r<0.02 for r=0.0.Comment: 15 pages, 12 figures, submitted to MNRA
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