Giuseppe Fanizza - November 10, 2016

Lensing and CMB: next-to-leading order corrections beyond the Born approximation

We investigate the weak lensing corrections to the cosmic microwave background
temperature anisotropies considering effects beyond the Born approximation. To
this aim, we use the small deflection angle approximation, to connect the lensed
and unlensed power spectra, via expressions for the deflection angles up to third
order in the gravitational potential. While the small deflection angle approximation
has the drawback to be reliable only for multipoles l < 2500, it allows us to
consistently take into account the non-Gaussian nature of cosmological perturbation
theory beyond the linear level. The contribution to the lensed temperature power
spectrum coming from the non-Gaussian nature of the deflection angle at higher order
is a new effect which has not been taken into account in the literature so far. It
turns out to be the leading contribution among the post-Born lensing corrections.