Can topological defects mimic the BICEP2 B-mode signal?
  We show that the B-mode polarization signal detected at low multipoles by
BICEP2 cannot be entirely due to topological defects. This would be
incompatible with the high-multipole B-mode polarization data and also with
existing temperature anisotropy data. Adding cosmic strings to a model with
tensors, we find that B-modes on their own provide a comparable limit on the
defects to that already coming from Planck satellite temperature data. We note
that strings at this limit give a modest improvement to the best-fit of the
B-mode data, at a somewhat lower tensor-to-scalar ratio of $r \simeq 0.15$.
