On vector mode contribution to CMB temperature and polarization from local strings

TL;DR

This paper corrects previous computational errors in modeling cosmic string effects on the CMB, revealing a stronger vector mode contribution and tighter constraints on string tension, with significant implications for B-mode polarization signals.

Contribution

It identifies and corrects errors in prior calculations, leading to revised, more stringent limits on cosmic string tension and enhanced understanding of their CMB polarization signatures.

Findings

Corrected code increases vector mode contribution to CMB anisotropies.

Stronger upper limit on cosmic string tension: Gμ < 1.8×10^{-7}.

Enhanced B-mode polarization amplitude could surpass lensing-induced signals.

Abstract

In a recent publication, we used the data from WMAP and SDSS to constrain the primordial perturbations and to predict the B-mode polarization sourced by cosmic string networks. We have been alerted by A. Slosar to the existence of errors in the code we used to calculate the Cosmic Microwave Background anisotropies from cosmic strings. Correcting the errors leads to a significant increase in the vector mode contribution to the CMB temperature and polarization anisotropies as well as an overall renormalization of the various string spectra. In these notes we explain the nature of the errors and discuss their implications for previously published constraints on cosmic strings based on this code. The chief change in our results is that our derived limit for the cosmic string tension is strengthened: G\mu < 1.8 (2.7) * 10^{-7} at 68 (95)% confidence. We also note that the newly-enhanced vector mode contribution produces a greatly-increased amplitude for B-mode polarization in the CMB which could exceed the B-mode power produced by the lensing of primordial E-mode polarization into B-mode polarization.