Dark Synergy: Gravitational Lensing and the CMB

With the launch of the MAP satellite and continuing progress in ground and balloon based experiments, cosmologists hope to soon be in a situation where cosmic microwave background (CMB) anisotropies have rmly established the adiabatic cold dark matter paradigm for structure formation and the parameters that govern it at high redshift. Attention on the experimental and theoretical front will increasingly turn to the potentially deeper questions at the two opposite ends of time: the energy contents of the universe and their clustering properties at recent epochs and the origins of structure perhaps in the inationary epoch. From distance measures to high redshift supernova [1] and indications of a near critical density universe from the CMB [2], there is increasingly strong evidence for an unknown component of dark energy that accelerates the expansion at low redshifts. In this context, it is useful to consider potential cosmological probes in light of what the primary CMB temperature anisotropies are and are not expected to reveal. While some parameters such as the physical baryon and non-relativistic matter density should be quite cleanly determined, others such as the dark energy properties, the epoch of reionization, and the gravitational wave amplitude are entangled with each other in parameter degeneracies. While the CMB polarization is one wellrecognized means of breaking some of these degeneracies, these issues are suciently important and polarization measurements suciently dicult that multiple independent approaches are desirable. In this Paper, we compare and contrast the ability of weak gravitational lensing in the shearing of faint galaxy images and distortions of the CMB temperature anisotropies in shedding light on these issues in the postprimary CMB epoch. Weak gravitational lensing shares with the primary anisotropies a unique status in cosmology in that its observables are in principle predictable ab initio given a cosmological model. Measurements are limited mainly by instrumental systematics rather than unknown astrophysics. As such lensing observables are well-suited to complement information from the CMB. Recent works [3{5] have shown that it is possible to map structures on the largest scales at high redshift through the lensing of the CMB. We evaluate here the utility of such measurements and their cross-correlation with the anisotropies themselves as well as cosmic shear for cosmological parameter estimation. On the cosmic shear side, we extend the work of [6] by considering correlations with CMB temperature anisotropies and lensing. We also utilize the extended parameter space of [7] to study the background and clustering properties of the dark energy. In this context, Huterer [8] has recently shown that the sub-arcminute regime provides substantial information on the dark energy but will require a better understanding of the power spectrum and its statistical properties in the deeply non-linear regime (e.g. [9]). Here we take the complementary tack of supplementing information in the translinear regime with source redshift information [10]. The outline of the paper is as follows: inxII we describe the the cosmological parameter space, power spectra and cross correlations of the observables and the Fisher formalism for parameter estimation forecasts. In xIII, we discuss the phenomenology of the lensing observables and their utility in breaking cosmological parameter degeneracies. We present parameter forecasts inxIV and conclude in xV. In the Appendix, we give tting formula