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 $\sim$ 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 $\sim$ 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 $w(z)\approx w_0 + z (dw/dz)_0$, we study the expected accuracy to which the equation of state today $w_0$ and its rate of change $(dw/dz)_0$ 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

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 $\times 10^{-2}$. The coupling parameter $\xi$ is strongly degenerate with the cold dark matter energy density $\Omega_{c}h^2$ and the Hubble constant $H_0$.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

Gravitational Lensing Limits on the Average Redshift of Submillimeter Sources

The submillimeter universe has now been explored with the Submillimeter Common User Bolometer Array (SCUBA) camera on the James Clerk Maxwell Telescope, and a claim has been made to the presence of a new population of optically unidentified starforming galaxies at high redshifts (z \gtrsim 3). Such a population dramatically alters current views on the star formation history of the universe as well as galaxy formation and evolution. Recently, new radio identifications of the Hubble Deep Field submm sources have led to the suggestion that some of these sources are at low redshifts, however, submm source redshift distribution is still not well determined. Here, we present an upper limit to the average redshift by comparing the expected number of gravitationally lensed submm sources due to foreground cluster potentials to current observed statistics of such lensed sources. The upper limit depends on the cosmological parameters, and at the 68% confidence level, < 3.1, 4.8, 5.2, or 8.0 for (Omega,Lambda) values of (0.3,0.7), (0.5,0.5), (0.3,0.0) or (1.0,0.0) respectively. These upper limits are consistent with redshift distribution for 850 micron sources implied by starformation history models based on measured background radiation at far-infrared and submm wavelengths.Comment: Accepted for publication in ApJ Letters (4 pages, including 1 table

Weak Lensing of the CMB: Cumulants of the Probability Distribution Function

We discuss the real-space moments of temperature anisotropies in the cosmic microwave background (CMB) due to weak gravitational lensing by intervening large-scale structure. We show that if the probability distribution function of primordial temperature anisotropies is Gaussian, then it remains unchanged after gravitational lensing. With finite resolution, however, non-zero higher-order cumulants are generated both by lensing autocorrelations and by cross-correlations between the lensing potential and secondary anisotropies in the CMB such as the Sunayev-Zel'dovich (SZ) effect. Skewness is produced by these lensing-SZ correlations, while kurtosis receives contributions from both lensing alone and lensing-SZ correlations. We show that if the projected lensing potential is Gaussian, all cumulants of higher-order than the kurtosis vanish. While recent results raise the possibility of detection of the skewness in upcoming data, the kurtosis will likely remain undetected.Comment: 11 pages, 4 figures, submitted to PR

A Lensing Reconstruction of Primordial Cosmic Microwave Background Polarization

We discuss a possibility to directly reconstruct the CMB polarization field at the last scattering surface by accounting for modifications imposed by the gravitational lensing effect. The suggested method requires a tracer field of the large scale structure lensing potentials that deflected propagating CMB photons from the last scattering surface. This required information can come from a variety of observations on the large scale structure matter distribution, including convergence reconstructed from lensing shear studies involving galaxy shapes. In the case of so-called curl, or B,-modes of CMB polarization, the reconstruction allows one to identify the distinct signature of inflationary gravitational waves.Comment: 6 pages, 2 figures; PRD submitte

Solar System: Sifting through the debris

A quadrillion previously unnoticed small bodies beyond Neptune have been spotted as they dimmed X-rays from a distant source. Models of the dynamics of debris in the Solar System's suburbs must now be reworked.Comment: 3 pages, 1 figure; Nature News and Views on Chang et al. 2006, Nature, 442, 660-66

Deciphering Inflation with Gravitational Waves: Cosmic Microwave Background Polarization vs. Direct Detection with Laser Interferometers

A detection of the primordial gravitational wave background is considered to be the ``smoking-gun '' evidence for inflation. While super-horizon waves are probed with cosmic microwave background (CMB) polarization, the relic background will be studied with laser interferometers. The long lever arm spanned by the two techniques improves constraints on the inflationary potential and validation of consistency relations expected under inflation. If gravitational waves with a tensor-to-scalar amplitude ratio greater than 0.01 are detected by the CMB, then a direct detection experiment with a sensitivity consistent with current concept studies should be pursued vigorously. If no primordial tensors are detected by the CMB, a direct detection experiment to understand the simplest form of inflation must have a sensitivity improved by two to three orders of magnitude over current plans.Comment: 6 pages, 2 color figures. replaced with published version. Full resolution figures are available at http://cfcp.uchicago.edu/~hiranya/CMB_BBO

Cosmology from supernova magnification maps

High-z Type Ia supernovae are expected to be gravitationally lensed by the foreground distribution of large-scale structure. The resulting magnification of supernovae is statistically measurable, and the angular correlation of the magnification pattern directly probes the integrated mass density along the line of sight. Measurements of cosmic magnification of supernovae therefore complements galaxy shear measurements in providing a direct measure of clustering of the dark matter. As the number of supernovae is typically much smaller than the number of sheared galaxies, the two-point correlation function of lensed Type Ia supernovae suffers from significantly increased shot noise. Neverthless, we find that the magnification map of a large sample of supernovae, such as that expected from next generation dedicated searches, will be easily measurable and provide an important cosmological tool. For example, a search over 20 sq. deg. over five years leading to a sample of ~ 10,000 supernovae would measure the angular power spectrum of cosmic magnification with a cumulative signal-to-noise ratio of ~20. This detection can be further improved once the supernova distance measurements are cross-correlated with measurements of the foreground galaxy distribution. The magnification maps made using supernovae can be used for important cross-checks with traditional lensing shear statistics obtained in the same fields, as well as help to control systematics. We discuss two applications of supernova magnification maps: the breaking of the mass-sheet degeneracy when estimating masses of shear-detected clusters, and constraining the second-order corrections to weak lensing observables.Comment: 4 pages, 2 figures, ApJL submitted; "Signal" discussed here is the extra covariance in astro-ph/050958