CMB anisotropies generated by cosmic string loops

TL;DR

This paper extends the Unconnected Segment Model to include cosmic string loops, enabling more accurate predictions of their contribution to CMB anisotropies, especially on small scales, with potential significance up to 10%.

Contribution

The authors develop an extended USM incorporating cosmic string loops and implement it in CMBACT to improve CMB anisotropy predictions.

Findings

Loops enhance small-scale anisotropies.

Vector modes from loops dominate at high multipoles.

Loop contributions can reach 10% of total anisotropies.

Abstract

We investigate the contribution of cosmic string loops to the Cosmic Microwave Background (CMB) anisotropies. This is done by extending the Unconnected Segment Model (USM) to include the contribution of the cosmic string loops created throughout the cosmological evolution of a cosmic string network to the stress-energy tensor. We then implement this extended USM in the publicly available CMBACT code and obtain the linear CDM power spectrum and the CMB angular power spectra generated by cosmic string loops. We find that the shape of the angular power spectra generated by loops is, in general, similar to that of long strings. However, there is generally an enhancement of the anisotropies on small angular scales. Vector modes produced by loops dominate over those produced by long strings for large multipole moments $\ell$. The contribution of loops to the CMB anisotropies generated by cosmic string networks may reach a level of $10\%$ for large loops but decreases as the size of loops decreases. This contribution may then be significant and, thus, this extension provides a more accurate prediction of the CMB anisotropies generated by cosmic string networks.