Large scale CMB anomalies from thawing cosmic strings

TL;DR

This paper explores how recently thawed cosmic strings could produce large-scale anomalies in the CMB, potentially explaining observed dipole modulations and cold spots without conflicting with existing constraints.

Contribution

It introduces a scenario where thawing cosmic strings generate large-scale CMB anisotropies, providing a novel explanation for observed anomalies.

Findings

Thawing cosmic strings can mimic dipole modulation in the CMB.

A few strings with tension ~10^(-6) can match Planck anomalies.

The scenario predicts a cold spot from string loops.

Abstract

Cosmic strings formed during inflation are expected to be either diluted over super-Hubble distances, i.e., invisible today, or to have crossed our past light cone very recently. We discuss the latter situation in which a few strings imprint their signature in the Cosmic Microwave Background (CMB) Anisotropies after recombination. Being almost frozen in the Hubble flow, these strings are quasi static and evade almost all of the previously derived constraints on their tension while being able to source large scale anisotropies in the CMB sky. Using a local variance estimator on thousand of numerically simulated Nambu-Goto all sky maps, we compute the expected signal and show that it can mimic a dipole modulation at large angular scales while being negligible at small angles. Interestingly, such a scenario generically produces one cold spot from the thawing of a cosmic string loop. Mixed with anisotropies of inflationary origin, we find that a few strings of tension GU = O(1) x 10^(-6) match the amplitude of the dipole modulation reported in the Planck satellite measurements and could be at the origin of other large scale anomalies.