Weak lensing of CMB by cosmic (super-)strings

TL;DR

This paper investigates how cosmic (super-)strings cause weak lensing effects on CMB anisotropies, revealing how string properties influence observable polarization and temperature spectra, especially at low multipoles.

Contribution

The authors develop a method to calculate the lensing convergence from cosmic strings and analyze how string properties affect CMB anisotropies, highlighting the impact of intercommuting probability.

Findings

Convergence spectrum peaks at low multipoles due to string segments at low redshifts.

Lower intercommuting probability increases the number density of string segments, enhancing lensing effects.

String-induced polarization spectra decay more slowly on small scales than standard inflationary perturbations.

Abstract

We study the effect of weak lensing by cosmic (super-)strings on the anisotropies of cosmic microwave background (CMB). In developing a method to calculate the lensing convergence field due to strings, and thereby temperature and polarization angular power spectra of CMB, we clarify how the nature of strings, characterized by the intercommuting probability, can influence these CMB anisotropies. Assuming that the power spectrum is dominated by Poisson-distributed string segments, we find that the convergence spectrum peaks at low multipoles and is mostly contributed from strings located at relatively low redshifts. As the intercommuting probability decreases, the spectra of the convergence and hence the lensed temperature and polarizations are gained because the number density of string segments becomes larger. An observationally important feature of the string-induced CMB polarizations is that the string-lensed spectra decay more slowly on small scales compared with primordial scalar perturbations from standard inflation.