Gravitational corrections to light propagation in a perturbed FLRW universe and corresponding weaklensing spectra
Abstract
When the gravitational lensing of the largescale structure is calculated from a cosmological model a few assumptions enter: (i) one assumes that the photons follow unperturbed background geodesics, which is usually referred to as the Born approximation, (ii) the lenses move slowly, (iii) the sourceredshift distribution is evaluated relative to the background quantities, and (iv) the lensing effect is linear in the gravitational potential. Even though these approximations are small individually they could sum up, especially since they include local effects such as the SachsWolfe and peculiar motion, but also nonlocal ones like the Born approximation and the integrated SachsWolfe effect. In this work, we will address all points mentioned and perturbatively calculate the effect on a tomographic cosmic shear power spectrum of each effect individually as well as all crosscorrelations. Our findings show that each effect is at least 45 orders of magnitude below the leading order lensing signal. Finally, we sum up all effects to estimate the overall impact on parameter estimation by a future cosmological weaklensing survey such as Euclid in a wcold dark matter cosmology with parametrization Ω_{m}, σ_{8}, n_{s}, h, w_{0}, and w_{a}, using five tomographic bins. We consistently find a parameter bias of 10^{5}, which is therefore completely negligible for all practical purposes, confirming that other effects such as intrinsic alignments, magnification bias and uncertainties in the redshift distribution will be the dominant systematic source in future surveys.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 June 2018
 DOI:
 10.1093/mnras/sty672
 arXiv:
 arXiv:1801.03325
 Bibcode:
 2018MNRAS.477..741C
 Keywords:

 gravitational lensing: weak;
 dark energy;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 doi:10.1093/mnras/sty672