Did BICEP2 see vector modes? First B-mode constraints on cosmic defects

Abstract: Scaling networks of cosmic defects, such as strings and textures, actively generate scalar, vector and tensor metric perturbations throughout the history of the universe. In particular, {\em vector} modes sourced by defects are an efficient source of the CMB B-mode polarization. We use the recently released BICEP2 and POLARBEAR B-mode polarization spectra to constrain properties of a wide range of different types of cosmic strings networks. We find that in order for strings to provide a satisfactory fit on their own, the effective inter-string distance needs to be extremely large -- spectra that fit the data best are more representative of global strings and textures. When a local string contribution is considered together with the inflationary B-mode spectrum, the fit is improved. We discuss implications of these results for theories that predict cosmic defects.