Weak lensing induced by second-order vector mode

Shohei Saga, Daisuke Yamauchi, Kiyotomo Ichiki

The vector mode of cosmological perturbation theory imprints characteristic signals on the weak lensing signals such as curl and B modes which are never imprinted by the scalar mode. However, the vector mode is neglected in the standard first-order cosmological perturbation theory since it only has a decaying mode. This situation changes if the cosmological perturbation theory is expanded up to second order. The second-order vector and tensor modes are inevitably induced by the product of the first-order scalar modes. We study the effect of the second-order vector mode on the weak lensing curl and B modes. We find that the curl mode induced by the second-order vector mode is comparable to that induced by the primordial gravitational waves with the tensor-to-scalar ratio ? =0.1 at ℓ ≈200. In this case, the curl mode induced by the second-order vector mode dominates at ℓ >200. Furthermore, the B-mode cosmic shear induced by the second-order vector mode dominates on almost all scales. However, we find that the observational signatures of the second-order vector and tensor modes cannot exceed the expected noise of ongoing and upcoming weak lensing measurements. We conclude that the curl and B modes induced by the second-order vector and tensor modes are unlikely to be detected in future experiments.

Physical Review D

92

063533

https://doi.org/10.1103/PhysRevD.92.063533

1505.02774