Constraints on the Nambu-Goto cosmic string contribution to the CMB
  power spectrum in light of new temperature and polarisation data
  Cosmic strings generate vector and tensor modes in the B-channel of
polarization, as well as the usual temperature power spectrum and E-mode
polarization spectrum. We use the power spectrum obtained from high-resolution
Nambu-Goto cosmic string simulations together with the Planck and BICEP2
likelihoods to explore the degeneracies appearing between cosmic strings and
other cosmological parameters in different inflationary scenarios, as well as
the constraints that can be imposed on cosmic strings in each of these
situations. In standard $\Lambda$CDM, the Planck likelihood yields an upper
limit $G\mu<1.49 \times 10^{-7}$ (95% confidence). We also analyse the
possibility of explaining the BB power spectrum signal recently detected by the
BICEP2 probe. We find that cosmic strings alone are able to explain only part
of the B-mode polarization signal. Apart from the standard $\Lambda$CDM model,
we look at the following non-minimal parameters: the running of the spectral
index, non-zero tensor-to-scalar ratio, additional degrees of freedom
($N_{eff}$) and sterile neutrinos. We find that in both Planck and BICEP2
scenarios adding $N_{eff}$ induces degeneracies between cosmic strings and
$N_{eff}$ and other $\Lambda$CDM parameters. With $N_{eff}$ a larger
contribution from cosmic strings is allowed, even favoured, but after combining
with large-scale structure data, such as BAOs, strings remain strongly
constrained.
