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