398 research outputs found

### Gravity and Non-gravity Modes in the VIRMOS-DESCART Weak Lensing Survey

We analyze the weak lensing data of the VIRMOS imaging survey using
projections (called E and B-modes) of the two independents observed correlation
functions. The E-mode contains all the lensing signal, while noise and
systematics contribute equally to the E and B modes provided that intrinsic
alignment is negligible. The mode separation allows a measurement of the signal
with a \sqrt{2} smaller error bars, and a separate channel to test for
systematic errors. We apply various transformations, including a spherical
harmonic space power spectrum C^E_l and C^B_l, which provides a direct
measurement of the projected dark matter distribution for 500<l<10^4.Comment: accepted version, minor changes, 18 pages including 6 figure

### Cross-Correlating Probes of Primordial Gravitational Waves

One of the most promising ways of detecting primordial gravitational waves
generated during inflation is to observe B-modes of polarization, generated by
Thomson scattering after reionization, in the cosmic microwave background
(CMB). Large scale foregrounds though are expected to be a major systematic
issue, so -- in the event of a tentative detection -- an independent
confirmation of large scale gravitational waves would be most welcome. Previous
authors have suggested searching for the analogous mode of cosmic shear in weak
lensing surveys but have shown that the signal to noise of this mode is
marginal at best. This argument is reconsidered here, accounting for the
cross-correlations of the polarization and lensing B-modes. A lensing survey
can potentially strengthen the argument for a detection of primordial
gravitational waves, although it is unlikely to help constrain the amplitude of
the signal.Comment: 13 pages, 8 figure

### Measuring the Deviation from the Linear and Deterministic Bias through Cosmic Gravitational Lensing Effects

Since gravitational lensing effects directly probe inhomogeneities of dark
matter, lensing-galaxy cross-correlations can provide us important information
on the relation between dark matter and galaxy distributions, i.e., the bias.
In this paper, we propose a method to measure the stochasticity/nonlinearity of
the galaxy bias through correlation studies of the cosmic shear and galaxy
number fluctuations. Specifically, we employ the aperture mass statistics
$M_{ap}$ to describe the cosmic shear. We divide the foreground galaxy redshift
$z_f<z_s$ into several bins, where $z_s$ is the redshift of the source
galaxies, and calculate the quantity $^2/$ for
each redshift bin. Then the ratio of the summation of $^2/<
N_g^2(z_f)>$ over the bins to $$ gives a measure of the
nonlinear/stochastic bias. Here $N_g(z_f)$ is the projected surface number
density fluctuation of foreground galaxies at redshift $z_f$, and $M_{ap}$ is
the aperture mass from the cosmic-shear analysis. We estimate that for a
moderately deep weak-lensing survey with $z_s=1$, source galaxy surface number
density $n_b=30 \hbox {gal}/\hbox {arcmin}^2$ and a survey area of $25 \hbox
{deg}^2$, the effective $r$-parameter that represents the deviation from the
linear and deterministic bias is detectable in the angular range of 1'-10' if
|r-1|\gsim 10%. For shallow, wide surveys such as the Sloan Digital Sky
Survey with $z_s=0.5$, $n_b=5 \hbox {gal}/\hbox {arcmin}^2$, and a survey area
of $10^4 \hbox {deg}^2$, a 10% detection of $r$ is possible over the angular
range $1'-100'$.Comment: ApJ in pres

### Cross-correlating CMB polarization with local large scale structures

We study heterogeneous quantities that efficiently cross-correlate the
lensing information encoded in CMB polarization and large-scale structures
recovered from weak lensing galaxy surveys. These quantities allow us to take
advantage of the special features of weak lensing effect on CMB B-polarization
and of the high (40%) cross-correlation between the two data sets. We show that
these objects are robust to filtering effects, have a low intrinsic cosmic
variance (around 8% for small 100 square degrees surveys) and can be used as an
original constraint on the vacuum energy density.Comment: 4 pages, use moriond.sty, to appear in the proceedings of the XXXVth
Rencontres de Moriond "Energy densities in the Universe

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