708 research outputs found
Dissipation and nonlocality in a general expanding braneworld universe
We study the evolution of both scalar and tensor cosmological perturbations
in a Randall-Sundrum braneworld having an arbitrary expansion history. We adopt
a four dimensional point of view where the degrees of freedom on the brane
constitute an open quantum system coupled to an environment composed of the
bulk gravitons. Due to the expansion of the universe, the brane degrees of
freedom and the bulk degrees of freedom interact as they propagate forward in
time. Brane excitations may decay through the emission of bulk gravitons which
may escape to future infinity, leading to a sort of dissipation from the four
dimensional point of view of an observer on the brane. Bulk gravitons may also
be reflected off of the curved bulk and reabsorbed by the brane, thereby
transformed into quanta on the brane, leading to a sort of nonlocality from the
four dimensional point of view. The dissipation and the nonlocality are encoded
into the retarded bulk propagator. We estimate the dissipation rates of the
bound state as well as of the matter degrees of freedom at different
cosmological epochs and for different sources of matter on the brane. We use a
near-brane limit of the bulk geometry for the study when purely nonlocal bulk
effects are encountered.Comment: v2, 34 pages, 7 figures, minor changes, comments and references
added, version to appear in Phys. Rev.
Extracting HI cosmological signal with Generalized Needlet Internal Linear Combination
HI intensity mapping is a new observational technique to map fluctuations in
the large-scale structure of matter using the 21 cm emission line of atomic
hydrogen (HI). Sensitive radio surveys have the potential to detect Baryon
Acoustic Oscillations (BAO) at low redshifts (z < 1) in order to constrain the
properties of dark energy. Observations of the HI signal will be contaminated
by instrumental noise and, more significantly, by astrophysical foregrounds,
such as Galactic synchrotron emission, which is at least four orders of
magnitude brighter than the HI signal. Foreground cleaning is recognised as one
of the key challenges for future radio astronomy surveys. We study the ability
of the Generalized Needlet Internal Linear Combination (GNILC) method to
subtract radio foregrounds and to recover the cosmological HI signal for a
general HI intensity mapping experiment. The GNILC method is a new technique
that uses both frequency and spatial information to separate the components of
the observed data. Our results show that the method is robust to the complexity
of the foregrounds. For simulated radio observations including HI emission,
Galactic synchrotron, Galactic free-free, radio sources and 0.05 mK thermal
noise, we find that we can reconstruct the HI power spectrum for multipoles 30
< l < 150 with 6% accuracy on 50% of the sky for a redshift z ~ 0.25.Comment: 20 pages, 13 figures. Updated to match version accepted by MNRA
Can we neglect relativistic temperature corrections in the Planck thermal SZ analysis?
Measurements of the thermal Sunyaev-Zel'dovich (tSZ) effect have long been
recognized as a powerful cosmological probe. Here we assess the importance of
relativistic temperature corrections to the tSZ signal on the power spectrum
analysis of the Planck Compton- map, developing a novel formalism to account
for the associated effects. The amplitude of the tSZ power spectrum is found to
be sensitive to the effective electron temperature, , of the cluster
sample. Omitting the corresponding modifications leads to an underestimation of
the -power spectrum amplitude. Relativistic corrections thus add to the
error budget of tSZ power spectrum observables such as . This could
help alleviate the tension between various cosmological probes, with the
correction scaling as for Planck. At the current level of
precision, this implies a systematic shift by , which can also
be interpreted as an overestimation of the hydrostatic mass bias by , bringing it into better
agreement with hydrodynamical simulations. It is thus time to consider
relativistic temperature corrections in the processing of current and future
tSZ data.Comment: 6 pages, 4 figures, minor changes, updated to match version accepted
by MNRA
Measurement of the pairwise kinematic Sunyaev-Zeldovich effect with Planck and BOSS data
We present a new measurement of the kinetic Sunyaev-Zeldovich effect (kSZ)
using Planck cosmic microwave background (CMB) and Baryon Oscillation
Spectroscopic Survey (BOSS) data. Using the `LowZ North/South' galaxy catalogue
from BOSS DR12, and the group catalogue from BOSS DR13, we evaluate the mean
pairwise kSZ temperature associated with BOSS galaxies. We construct a `Central
Galaxies Catalogue' (CGC) which consists of isolated galaxies from the original
BOSS data set, and apply the aperture photometry (AP) filter to suppress the
primary CMB contribution. By constructing a halo model to fit the pairwise kSZ
function, we constrain the mean optical depth to be
for `LowZ North CGC',
for `LowZ South CGC', and
for `DR13 Group'. In
addition, we vary the radius of the AP filter and find that the AP size of
gives the maximum detection for . We also
investigate the dependence of the signal with halo mass and find
and
for `DR13 Group' with halo
mass restricted to, respectively, less and greater than its median halo mass,
. For the `LowZ North CGC' sample restricted
to there is no detection of
the kSZ signal because these high mass halos are associated with the
high-redshift galaxies of the LowZ North catalogue, which have limited
contribution to the pairwise kSZ signals.Comment: 11 pages, 11 figures, 2 table
Sensitivity and foreground modelling for large-scale CMB B-mode polarization satellite missions
The measurement of the large-scale B-mode polarization in the cosmic
microwave background (CMB) is a fundamental goal of future CMB experiments.
However, because of unprecedented sensitivity, future CMB experiments will be
much more sensitive to any imperfect modelling of the Galactic foreground
polarization in the reconstruction of the primordial B-mode signal. We compare
the sensitivity to B-modes of different concepts of CMB satellite missions
(LiteBIRD, COrE, COrE+, PRISM, EPIC, PIXIE) in the presence of Galactic
foregrounds. In particular, we quantify the impact on the tensor-to-scalar
parameter of incorrect foreground modelling in the component separation
process. Using Bayesian fitting and Gibbs sampling, we perform the separation
of the CMB and Galactic foreground B-modes. The recovered CMB B-mode power
spectrum is used to compute the likelihood distribution of the tensor-to-scalar
ratio. We focus the analysis to the very large angular scales that can be
probed only by CMB space missions, i.e. the Reionization bump, where primordial
B-modes dominate over spurious B-modes induced by gravitational lensing. We
find that fitting a single modified blackbody component for thermal dust where
the "real" sky consists of two dust components strongly bias the estimation of
the tensor-to-scalar ratio by more than 5{\sigma} for the most sensitive
experiments. Neglecting in the parametric model the curvature of the
synchrotron spectral index may bias the estimated tensor-to-scalar ratio by
more than 1{\sigma}. For sensitive CMB experiments, omitting in the foreground
modelling a 1% polarized spinning dust component may induce a non-negligible
bias in the estimated tensor-to-scalar ratio.Comment: 20 pages, 8 figures, 6 tables. Updated to match version accepted by
MNRA
Mapping the relativistic electron gas temperature across the sky
With increasing sensitivity, angular resolution, and frequency coverage,
future cosmic microwave background (CMB) experiments like PICO will allow us to
access new information about galaxy clusters through the relativistic thermal
Sunyaev-Zeldovich (SZ) effect. We will be able to map the temperature of
relativistic electrons across the entire sky, going well beyond a simple
detection of the relativistic SZ effect by cluster stacking methods that
currently define the state-of-the-art. Here, we propose a new map-based
approach utilizing SZ-temperature moment expansion and constrained-ILC methods
to extract electron gas temperature maps from foreground-obscured CMB data.
This delivers a new independent map-based observable, the electron temperature
power spectrum , which can be used to constrain cosmology
in addition to the Compton- power spectrum . We find
that PICO has the required sensitivity, resolution, and frequency coverage to
accurately map the electron gas temperature of galaxy clusters across the full
sky, covering a broad range of angular scales. Frequency-coverage at
plays an important role for extracting the
relativistic SZ effect in the presence of foregrounds. For Coma, PICO will
allow us to directly reconstruct the electron temperature profile using the
relativistic SZ effect. Coma's average electron temperature will be measured to
significance after foreground removal using PICO. Low-angular
resolution CMB experiment like LiteBIRD could achieve to
measurement of the electron temperature of this largest cluster. Our analysis
highlights a new spectroscopic window into the thermodynamic properties of
galaxy clusters and the diffuse electron gas at large angular scales.Comment: 17 pages, 18 figures, updated to match version accepted by MNRA
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