157 research outputs found
Weak Lensing of the Cosmic Microwave Background by Foreground Gravitational Waves
Weak lensing distortion of the background cosmic microwave background (CMB)
temperature and polarization patterns by the foreground density fluctuations is
well studied in the literature. We discuss the gravitational lensing
modification to CMB anisotropies and polarization by a stochastic background of
primordial gravitational waves between us and the last scattering surface.
While density fluctuations perturb CMB photons via gradient-type deflections
only, foreground gravitational waves distort CMB anisotropies via both
gradient- and curl-type displacements. The latter is a rotation of background
images, while the former is related to the lensing convergence. For a
primordial background of inflationary gravitational waves, with an amplitude
corresponding to a tensor-to-scalar ratio below the current upper limit of
0.3, the resulting modifications to the angular power spectra of CMB
temperature anisotropy and polarization are below the cosmic variance limit. At
tens of arcminute angular scales and below, these corrections, however, are
above the level at which systematics must be controlled in all-sky anisotropy
and polarization maps with no instrumental noise and other secondary and
foreground signals.Comment: 11 pages, 4 figures; Revised version updates the numerical
calculation for several corrections to the analytical formulation of lensing
by foreground gravitational waves. Main conclusions unchanged. Version
accepted for publication in Phys. Rev.
Gravitational Lensing as a Probe of Quintessence
A large number of cosmological studies now suggest that roughly two-thirds of
the critical energy density of the Universe exists in a component with negative
pressure. If the equation of state of such an energy component varies with
time, it should in principle be possible to identify such a variation using
cosmological probes over a wide range in redshift. Proper detection of any time
variation, however, requires cosmological probes beyond the currently studied
range in redshift of 0.1 to 1. We extend our analysis to gravitational
lensing statistics at high redshift and suggest that a reliable sample of
lensed sources, out to a redshift of 5, can be used to constrain the
variation of the equation of state, provided that both the redshift
distribution of lensed sources and the selection function involved with the
lensed source discovery process are known. An exciting opportunity to catalog
an adequate sample of lensed sources (quasars) to probe quintessence is now
available with the ongoing Sloan Digital Sky Survey. Writing , we study the expected accuracy to which the equation of state
today and its rate of change can simultaneously be
constrained. Such a determination can rule out some missing-energy candidates,
such as classes of quintessence models or a cosmological constant.Comment: Accepted for publication in ApJ Letters (4 pages, including 4
figures
Gravitational Lensing and the Hubble Deep Field
We calculate the expected number of multiply-imaged galaxies in the Hubble
Deep Field (HDF), using photometric redshift information for galaxies with m_I
< 27 that were detected in all four HDF passbands. A comparison of these
expectations with the observed number of strongly lensed galaxies constrains
the current value of Omega_m-Omega_Lambda, where Omega_m is the mean mass
density of the universe and Omega_Lambda is the normalized cosmological
constant. Based on current estimates of the HDF luminosity function and
associated uncertainties in individual parameters, our 95% confidence lower
limit on Omega_m-Omega_Lambda ranges between -0.44, if there are no strongly
lensed galaxies in the HDF, and -0.73, if there are two strongly lensed
galaxies in the HDF. If the only lensed galaxy in the HDF is the one presently
viable candidate, then, in a flat universe (Omega_m+Omega_Lambda=1),
Omega_Lambda < 0.79 (95% C.L.). These limits are compatible with estimates
based on high-redshift supernovae and with previous limits based on
gravitational lensing.Comment: 4 pages (aipproc.sty), 2 figures. To appear in "After the dark ages:
when galaxies were young," proceedings of the 9th Annual October Astrophysics
Conference, eds. S. S. Holt & E. P. Smit
Future weak lensing constraints in a dark coupled universe
Coupled cosmologies can predict values for the cosmological parameters at low
redshifts which may differ substantially from the parameters values within
non-interacting cosmologies. Therefore, low redshift probes, as the growth of
structure and the dark matter distribution via galaxy and weak lensing surveys
constitute a unique tool to constrain interacting dark sector models. We focus
here on weak lensing forecasts from future Euclid and LSST-like surveys
combined with the ongoing Planck cosmic microwave background experiment. We
find that these future data could constrain the dimensionless coupling to be
smaller than a few . The coupling parameter is strongly
degenerate with the cold dark matter energy density and the
Hubble constant .These degeneracies may cause important biases in the
cosmological parameter values if in the universe there exists an interaction
among the dark matter and dark energy sectors.Comment: 8 pages, 6 figure
Non-Gaussian Covariance of CMB B-modes of Polarization and Parameter Degradation
The B-mode polarization lensing signal is a useful probe of the neutrino mass
and to a lesser extent the dark energy equation of state as the signal depends
on the integrated mass power spectrum between us and the last scattering
surface. This lensing B-mode signal, however, is non-Gaussian and the resulting
non-Gaussian covariance to the power spectrum cannot be ignored as correlations
between B-mode bins are at a level of 0.1. For temperature and E-mode
polarization power spectra, the non-Gasussian covariance is not significant,
where we find correlations at the 10^{-5} level even for adjacent bins. The
resulting degradation on neutrino mass and dark energy equation of state is
about a factor of 2 to 3 when compared to the case where statistics are simply
considered to be Gaussian. We also discuss parameter uncertainties achievable
in upcoming experiments and show that at a given angular resolution for
polarization observations, increasing the sensitivity beyond a certain noise
value does not lead to an improved measurement of the neutrino mass and dark
energy equation of state with B-mode power spectrum. For Planck, the resulting
constraints on the sum of the neutrino masses is ~ 0.2 eV and on the dark
energy equation of state parameter we find, sigma_w ~ 0.5.Comment: 11 pages, 5 figures, minor changes, submitted to PR
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