1,569 research outputs found
Dark energy and CMB bispectrum
We consider the CMB bispectrum signal induced by structure formation through
the correlation between the Integrated Sachs-Wolfe and the weak lensing effect.
We investigate how the bispectrum knowledge can improve our knowledge of the
most important cosmological parameters, focusing on the dark energy ones.
Preliminary results suggest a consistent improvement on the estimation of dark
energy abundance and on dynamical properties of the equation of state.Comment: 6 pages, 5 figures. To appear in "Impact of Gravitational Lensing on
Cosmology", IAU Symposium 225, Mellier & Meylan ed
Impact of foregrounds on Cosmic Microwave Background maps
We discuss the possible impact of astrophysical foregrounds on three recent
exciting results of Cosmic Microwave Background (CMB) experiments: the WMAP
measurements of the temperature-polarization (TE) correlation power spectrum,
the detection of CMB polarization fluctuations on degree scales by the DASI
experiment, and the excess power on arcminute scales reported by the CBI and
BIMA groups. A big contribution from the Galactic synchrotron emission to the
TE power spectrum on large angular scales is indeed expected, in the lower
frequency WMAP channels, based on current, albeit very uncertain, models; at
higher frequencies the rapid decrease of the synchrotron signal may be, to some
extent, compensated by polarized dust emission. Recent measurements of
polarization properties of extragalactic radio sources at high radio frequency
indicate that their contamination of the CMB polarization on degree scales at
30 GHz is substantially below the expected CMB E-mode amplitude. Adding the
synchrotron contribution, we estimate that the overall foreground contamination
of the signal detected by DASI may be significant but not dominant. The excess
power on arc-min scales detected by the BIMA experiment may be due to
galactic-scale Sunyaev-Zeldovich effects, if the proto-galactic gas is heated
to its virial temperature and its cooling time is comparable to the Hubble time
at the epoch of galaxy formation. A substantial contamination by radio sources
of the signal reported by the CBI group on scales somewhat larger than BIMA's
cannot be easily ruled out.Comment: 10 pages, 5 figures, to appear in proc. int. conf. "Thinking,
Observing and Mining the Universe", Sorrento, Sept. 200
What's Behind Acoustic Peaks in the Cosmic Microwave Background Anisotropies
We give a brief review of the physics of acoustic oscillations in Cosmic
Microwave Background (CMB) anisotropies. As an example of the impact of their
detection in cosmology, we show how the present data on CMB angular power
spectrum on sub-degree scales can be used to constrain dark energy cosmological
models.Comment: 6 pages, proceedings to the TAUP2001 conference, LNGS, Italy, Sept.
200
Constraints on coupled dark energy using CMB data from WMAP and SPT
We consider the case of a coupling in the dark cosmological sector, where a
dark energy scalar field modifies the gravitational attraction between dark
matter particles. We find that the strength of the coupling {\beta} is
constrained using current Cosmic Microwave Background (CMB) data, including
WMAP7 and SPT, to be less than 0.063 (0.11) at 68% (95%) confidence level.
Further, we consider the additional effect of the CMB-lensing amplitude,
curvature, effective number of relativistic species and massive neutrinos and
show that the bound from current data on {\beta} is already strong enough to be
rather stable with respect to any of these variables. The strongest effect is
obtained when we allow for massive neutrinos, in which case the bound becomes
slightly weaker, {\beta} < 0.084(0.14). A larger value of the effective number
of relativistic degrees of freedom favors larger couplings between dark matter
and dark energy as well as values of the spectral index closer to 1. Adding the
present constraints on the Hubble constant, as well as from baryon acoustic
oscillations and supernovae Ia, we find {\beta} < 0.050(0.074). In this case we
also find an interesting likelihood peak for {\beta} = 0.041 (still compatible
with 0 at 1{\sigma}). This peak comes mostly from a slight difference between
the Hubble parameter HST result and the WMAP7+SPT best fit. Finally, we show
that forecasts of Planck+SPT mock data can pin down the coupling to a precision
of better than 1% and detect whether the marginal peak we find at small non
zero coupling is a real effect.Comment: 22 pages, 17 figure
Digital Deblurring of CMB Maps II: Asymmetric Point Spread Function
In this second paper in a series dedicated to developing efficient numerical
techniques for the deblurring Cosmic Microwave Background (CMB) maps, we
consider the case of asymmetric point spread functions (PSF). Although
conceptually this problem is not different from the symmetric case, there are
important differences from the computational point of view because it is no
longer possible to use some of the efficient numerical techniques that work
with symmetric PSFs. We present procedures that permit the use of efficient
techniques even when this condition is not met. In particular, two methods are
considered: a procedure based on a Kronecker approximation technique that can
be implemented with the numerical methods used with symmetric PSFs but that has
the limitation of requiring only mildly asymmetric PSFs. The second is a
variant of the classic Tikhonov technique that works even with very asymmetric
PSFs but that requires discarding the edges of the maps. We provide details for
efficient implementations of the algorithms. Their performance is tested on
simulated CMB maps.Comment: 9 pages, 13 Figure
Sub-degree CMB anisotropies from inflationary bubbles
It is well known that processes of first order phase transitions may have
occurred in the inflationary era. If one or more occurred well before the end
of inflation, the nucleated bubbles are stretched to large scales and the
primordial power spectrum contains a scale dependent non-Gaussian component
provided by the remnants of the bubbles. We predict the anisotropies in the
cosmic microwave background (CMB) induced by inflationary bubbles. We build a
general analytic model for describing a bubbly perturbation; we evolve each
Fourier mode using the linear theory of perturbations from reheating until
decoupling; we get the CMB anisotropies by considering the bubbly perturbation
intersecting the last scattering surface. The CMB image of an inflationary
bubble is a series of concentric isothermal rings of different color (sign of
) on the scale of the sound horizon at decoupling ( in
the sky); the resulting anisotropy is therefore strongly non-Gaussian. The mean
amplitude of for a bubble of size follows the known estimates
for linear perturbations, . In particular, bubbles with size corresponding to the seeds of
the observed large scale voids (tens of comoving Mpc) induce an interesting
pattern of CMB anisotropies on the sub-degree angular scale, to be further
investigated and compared with the forthcoming high resolution CMB maps
provided by the MAP and the Planck experiments.Comment: 10 pages, 5 postscript figures, accepted by Ap.
WMAP 3yr data with the CCA: anomalous emission and impact of component separation on the CMB power spectrum
The Correlated Component Analysis (CCA) allows us to estimate how the
different diffuse emissions mix in CMB experiments, exploiting also
complementary information from other surveys. It is especially useful to deal
with possible additional components. An application of CCA to WMAP maps
assuming that only the canonical Galactic emissions are present, highlights the
widespread presence of a spectrally flat "synchrotron" component, largely
uncorrelated with the synchrotron template, suggesting that an additional
foreground is indeed required. We have tested various spectral shapes for such
component, namely a power law as expected if it is flat synchrotron, and two
spectral shapes that may fit the spinning dust emission: a parabola in the logS
- log(frequency) plane, and a grey body. Quality tests applied to the
reconstructed CMB maps clearly disfavour two of the models. The CMB power
spectra, estimated from CMB maps reconstructed exploiting the three surviving
foreground models, are generally consistent with the WMAP ones, although at
least one of them gives a significantly higher quadrupole moment than found by
the WMAP team. Taking foreground modeling uncertainties into account, we find
that the mean quadrupole amplitude for the three "good" models is less than 1
sigma below the expectation from the standard LambdaCDM model. Also the other
reported deviations from model predictions are found not to be statistically
significant, except for the excess power at l~40. We confirm the evidence for a
marked North-South asymmetry in the large scale (l < 20) CMB anisotropies. We
also present a first, albeit preliminary, all-sky map of the "anomalous"
component.Comment: 14 pages, 17 figures, submitted to MNRAS, references adde
CMB signal in WMAP 3yr data with FastICA
We present an application of the fast Independent Component Analysis
(FastICA) to the WMAP 3yr data with the goal of extracting the CMB signal. We
evaluate the confidence of our results by means of Monte Carlo simulations
including CMB, foreground contaminations and instrumental noise specific of
each WMAP frequency band. We perform a complete analysis involving all or a
subset of the WMAP channels in order to select the optimal combination for CMB
extraction, using the frequency scaling of the reconstructed component as a
figure of merit. We found that the combination KQVW provides the best CMB
frequency scaling, indicating that the low frequency foreground contamination
in Q, V and W bands is better traced by the emission in the K band. The CMB
angular power spectrum is recovered up to the degree scale, it is consistent
within errors for all WMAP channel combination considered, and in close
agreement with the WMAP 3yr results. We perform a statistical analysis of the
recovered CMB pattern, and confirm the sky asymmetry reported in several
previous works with independent techniques.Comment: 10 pages, 7 figures, submitted to MNRA
Detectability of the Cross-Correlation between CMB Lensing and Stochastic GW Background from Compact Object Mergers
The anisotropies of the Stochastic Gravitational-Wave Background (SGWB), produced by merging compact binaries, constitute a possible new probe of the Large-Scale Structure (LSS). However, the significant shot noise contribution caused by the discreteness of the GW sources and the poor angular resolution of the instruments hampers the detection of the intrinsic anisotropies induced by the LSS. In this work, we investigate the potential of cross-correlating forthcoming high precision measurements of the SGWB energy density and the Cosmic Microwave Background (CMB) lensing convergence to mitigate the effect of shot noise. Combining a detailed model of stellar and galactic astrophysics with a novel framework to distribute the GW emitters in the sky, we compute the auto-and cross-correlation power spectra for the two cosmic fields, evaluate the shot noise contribution and predict the signal-to-noise ratio. The results of our analysis show that the SGWB energy density correlates significantly with the CMB lensing convergence and that the cross-correlation between these two cosmic fields reduces the impact of instrumental and shot noise. Unfortunately, the S/N is not high enough to detect the intrinsic SGWB anisotropies. Nevertheless, a network composed of both present and future generation GW interferometers, operating for at least 10 yrs, should be able to measure the shot noise contribution
Imprints of Primordial Voids on the CMB
We generalize in several ways the results existing in the literature: a) we
make use of an exact general relativistic solution for a spherical, nearly
empty cavity in the matter dominated era to evaluate the null geodesics and the
Sachs-Wolfe effect; b) we evaluate the magnitude of the adiabatic fluctuations
of the photon-baryon plasma; c) we study the influence of the shell profile;
and d) we take into account the finite thickness of the last scattering surface
(LSS) and the influence of its position with respect to the void center. We
find empirically an analytic approximation to the Sachs-Wolfe effect for all
crossing geometries and we derive an upper limit of 25 Mpc
for the comoving radii of voids sitting on the LSS in order to achieve
compatibility with COBE's data. As a nearly empty void has an overcomoving
expansion of a factor of 4 between decoupling and the present, the
maximum allowed size at present is 100 Mpc. On the other
hand, the smallness of the comoving size relative to the sound horizon reduces
strongly the adiabatic effect by Silk damping and makes it negligible. Most of
the signature of primordial voids comes therefore from metric effects and
consists of subdegree spots blue or red depending on whether the center lies
beyond or within the LSS. In conclusion we refine and confirm earlier
constraints on a power law void spectrum originated in an inflationary phase
transition and capable of generating the observed large scale structure.Comment: 14 pages, 5 figures, submitted to Montly Notice
- …