Constraining topological defects with temperature and polarization anisotropies

TL;DR

This study investigates the role of topological defects in cosmic microwave background anisotropies, finding that textures can fit data nearly as well as tensors, but strings are less favored, with dust foregrounds remaining significant.

Contribution

It provides updated constraints on topological defects' contributions to CMB anisotropies, considering combined temperature, polarization, dust foregrounds, and inflationary components.

Findings

Textures fit the data nearly as well as tensors.

Abelian Higgs strings are ruled out as the sole source of B-mode polarization.

Upper limits on defect parameters are tightened, with dust foregrounds remaining important.

Abstract

We analyse the possible contribution of topological defects to cosmic microwave anisotropies, both temperature and polarisation. We allow for the presence of both inflationary scalars and tensors, and of polarised dust foregrounds that may contribute to or dominate the B-mode polarisation signal. We confirm and quantify our previous statements that topological defects on their own are a poor fit to the B-mode signal. However, adding topological defects to a models with a tensor component or a dust component improves the fit around $\ell=200$. Fitting simultaneously to both temperature and polarisation data, we find that textures fit almost as well as tensors ($\Delta\chi^2 = 2.0$), while Abelian Higgs strings are ruled out as the sole source of the B-mode signal at low $\ell$. The 95% confidence upper limits on models combining defects and dust are $G\mu < 2.7\times 10^{-7}$ (Abelian Higgs strings), $G\mu < 9.8\times 10^{-7}$ (semilocal strings) and $G\mu < 7.3\times 10^{-7}$ (textures), a small reduction on the $Planck$ bounds. The most economical fit overall is obtained by the standard $\Lambda$CDM model with a polarised dust component.