We analyze the possible contribution of topological defects to cosmic microwave anisotropies, both temperature and polarization. We allow for the presence of both inflationary scalars and tensors, and of polarized dust foregrounds that may contribute to or dominate the B-mode polarization 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 model with a tensor component or a dust component improves the fit around $\ell =200$. Fitting simultaneously to both temperature and polarization data, we find that textures fit almost as well as tensors ($\mathrm{\Delta }{\chi }^2=2.0$), 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 $\mathrm{\Lambda }$–cold dark matter model with a polarized dust component.

• Received 21 August 2014

DOI:https://doi.org/10.1103/PhysRevD.90.103504