129 research outputs found

### GRAVITATIONAL LENSING EFFECT ON COSMIC MICROWAVE BACKGROUND ANISOTROPIES: A POWER SPECTRUM APPROACH

The effect of gravitational lensing on cosmic microwave background (CMB)
anisotropies is investigated using the power spectrum approach. The lensing
effect can be calculated in any cosmological model by specifying the evolution
of gravitational potential. Previous work on this subject is generalized to a
non-flat universe and to a nonlinear evolution regime. Gravitational lensing
cannot change the gross distribution of CMB anisotropies, but it may
redistribute the power and smooth the sharp features in the CMB power spectrum.
The magnitude of this effect is estimated using observational constraints on
the power spectrum of gravitational potential from galaxy and cluster surveys
and also using the limits on correlated ellipticities in distant galaxies. For
realistic CMB power spectra the effect on CMB multipole moments is less then a
few percent on degree angular scales, but gradually increases towards smaller
scales. On arcminute angular scales the acoustic oscillation peaks may be
partially or completely smoothed out because of the gravitational lensing.Comment: extended and corrected appendix, minor revisions of main text,
revised figure

### Wide Angle Effects in Future Galaxy Surveys

Current and future galaxy surveys cover a large fraction of the entire sky
with a significant redshift range, and the recent theoretical development shows
that general relativistic effects are present in galaxy clustering on very
large scales. This trend has renewed interest in the wide angle effect in
galaxy clustering measurements, in which the distant-observer approximation is
often adopted. Using the full wide-angle formula for computing the
redshift-space correlation function, we show that compared to the sample
variance, the deviation in the redshift-space correlation function from the
simple Kaiser formula with the distant-observer approximation is negligible in
galaxy surveys such as the SDSS, Euclid and the BigBOSS, if the theoretical
prediction from the Kaiser formula is properly averaged over the survey volume.
We also find corrections to the wide-angle formula and clarify the confusion in
literature between the wide angle effect and the velocity contribution in
galaxy clustering. However, when the FKP method is applied, substantial
deviations can be present in the power spectrum analysis in future surveys, due
to the non-uniform distribution of galaxy pairs.Comment: 17 pages, 11 figures, accepted for publication in MNRA

### The Sunyaev-Zel'dovich angular power spectrum as a probe of cosmological parameters

The angular power spectrum of the SZ effect, C_l, is a powerful probe of
cosmology. It is easier to detect than individual clusters in the field, is
insensitive to observational selection effects and does not require a
calibration between cluster mass and flux, reducing the systematic errors which
dominate the cluster-counting constraints. It receives a dominant contribution
from cluster region between 20-40% of the virial radius and is thus insensitive
to the poorly known gas physics in the cluster centre, such as cooling or
(pre)heating. In this paper we derive a refined analytic prediction for C_l
using the universal gas-density and temperature profile and the dark-matter
halo mass function. The predicted C_l has no free parameters and fits all of
the published hydrodynamic simulation results to better than a factor of two
around l=3000. We find that C_l scales as (sigma_8)^7 times (Omega_b h)^2 and
is almost independent of all of the other cosmological parameters. This differs
from the local cluster abundance studies, which give a relation between sigma_8
and Omega_m. We also compute the covariance matrix of C_l using the halo model
and find a good agreement relative to the simulations. We estimate how well we
can determine sigma_8 with sampling-variance-limited observations and find that
for a several-square-degree survey with 1-2 arcminute resolution one should be
able to determine sigma_8 to within a few percent, with the remaining
uncertainty dominated by theoretical modelling. If the recent excess of the CMB
power on small scales reported by the CBI experiment is due to the SZ effect,
then we find sigma_8(Omega_b h/0.029)^0.3 = 1.04 +- 0.12 at the 95% confidence
level (statistical) and with a residual 10% systematic (theoretical)
uncertainty.Comment: 17 pages, 14 figures, 1 table, sigma8 constraint including CBI and
BIMA, matches the accepted version in MNRA

### Primordial non-Gaussianity from the large scale structure

Primordial non-Gaussianity is a potentially powerful discriminant of the
physical mechanisms that generated the cosmological fluctuations observed
today. Any detection of non-Gaussianity would have profound implications for
our understanding of cosmic structure formation. In this paper, we review past
and current efforts in the search for primordial non-Gaussianity in the large
scale structure of the Universe.Comment: Invited review article for the CQG special issue on nonlinear
cosmological perturbations

### Signature of primordial non-Gaussianity of phi^3-type in the mass function and bias of dark matter haloes

We explore the effect of a cubic correction gnl*phi^3 on the mass function
and bias of dark matter haloes extracted from a series of large N-body
simulations and compare it to theoretical predictions. Such cubic terms can be
motivated in scenarios like the curvaton model, in which a large cubic
correction can be produced while simultaneously keeping the quadratic fnl*phi^2
correction small. The deviation from the Gaussian halo mass function is in
reasonable agreement with the theoretical predictions. The scale-dependent bias
correction Delta b_kappa(k,gnl) measured from the auto- and cross-power
spectrum of haloes, is similar to the correction in fnl models, but the
amplitude is lower than theoretical expectations. Using the compilation of LSS
data in Slosar et al. (2008), we obtain for the first time a limit on gnl of
-3.5*10^5 < gnl < +8.2*10^5 (at 95% CL). This limit will improve with the
future LSS data by 1-2 orders of magnitude, which should test many of the
scenarios of this type.Comment: 21 pages, 11 figures (v2): typo corrected, clarifications+references
added (v3): paper somewhat reorganized, added discussion on initial
conditions, version accepted by PR

### Primordial non-Gaussianity in the large scale structure of the Universe

Primordial non-Gaussianity is a potentially powerful discriminant of the
physical mechanisms that generated the cosmological fluctuations observed
today. Any detection of significant non-Gaussianity would thus have profound
implications for our understanding of cosmic structure formation. The large
scale mass distribution in the Universe is a sensitive probe of the nature of
initial conditions. Recent theoretical progress together with rapid
developments in observational techniques will enable us to critically confront
predictions of inflationary scenarios and set constraints as competitive as
those from the Cosmic Microwave Background. In this paper, we review past and
current efforts in the search for primordial non-Gaussianity in the large scale
structure of the Universe.Comment: 24 pages, 10 figures. To appear in the special issue "Testing the
Gaussianity and Statistical Isotropy of the Universe" of Advances in
Astronom

### A Line of Sight Approach to Cosmic Microwave Background Anisotropies

We present a new method for calculating linear cosmic microwave background
(CMB) anisotropy spectra based on integration over sources along the photon
past light cone. In this approach the temperature anisotropy is written as a
time integral over the product of a geometrical term and a source term. The
geometrical term is given by radial eigenfunctions which do not depend on the
particular cosmological model. The source term can be expressed in terms of
photon, baryon and metric perturbations, all of which can be calculated using a
small number of differential equations. This split clearly separates between
the dynamical and geometrical effects on the CMB anisotropies. More
importantly, it allows to significantly reduce the computational time compared
to standard methods. This is achieved because the source term, which depends on
the model and is generally the most time consuming part of calculation, is a
slowly varying function of wavelength and needs to be evaluated only in a small
number of points. The geometrical term, which oscillates much more rapidly than
the source term, does not depend on the particular model and can be precomputed
in advance. Standard methods that do not separate the two terms and require a
much higher number of evaluations. The new method leads to about two orders of
magnitude reduction in CPU time when compared to standard methods and typically
requires a few minutes on a workstation for a single model. The method should
be especially useful for accurate determinations of cosmological parameters
from CMB anisotropy and polarization measurements that will become possible
with the next generation of experiments. A programm implementing this method
can be obtained from the authors.Comment: 20 pages, 5 figures. Fortran code available from the author

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