Effects of cosmic strings with delayed scaling on CMB anisotropy

TL;DR

This paper investigates how cosmic strings with delayed scaling influence CMB anisotropies, showing that their effects are diminished if they enter the scaling regime after recombination, thus relaxing existing constraints.

Contribution

It provides a qualitative analysis of delayed scaling cosmic strings and demonstrates their reduced impact on CMB anisotropies, affecting constraints on string tension and inflationary parameters.

Findings

Delayed scaling reduces CMB anisotropy signals from cosmic strings.

Constraints on cosmic string tension are relaxed due to delayed scaling.

Cosmic strings alone cannot fully explain recent B-mode polarization observations.

Abstract

The network of cosmic strings generated in a phase transition during inflation enters the scaling regime later than that of usual strings. If it occurs after the recombination, temperature anisotropies of the cosmic microwave background (CMB) at high multipole moments are significantly reduced. In this paper, we study such effects qualitatively and show that the constraint on the cosmic string tension from the CMB temperature anisotropies and B-mode polarizations can be relaxed. It is shown to be difficult to explain the recent BICEP2 and POLARBEAR results in terms of signals induced by cosmic strings alone even if we take into account the delayed scaling. However, the inflationary tensor-to-scalar ratio required to explain the observed B-mode signals can be slightly reduced to be consistent with the Planck constraint.