Degeneracy between primordial tensor modes and cosmic strings in future CMB data from the Planck satellite

While observations indicate that the predominant source of cosmic inhomogeneities are adiabatic perturbations, there are a variety of candidates to provide auxiliary trace effects, including inflation-generated primordial tensors and cosmic defects which both produce B-mode cosmic microwave background polarization. We investigate whether future experiments may suffer confusion as to the true origin of such effects, focusing on the ability of Planck to distinguish tensors from cosmic strings, and show that there is no significant degeneracy.

Figure 1

The CMB temperature and polarization power spectra contributions from inflationary scalar modes (black, dashed), inflationary tensor modes (black, solid), and cosmic strings (gray, dotted-dashed) [13]. The inflationary tensors have $r=0.04$ while the string contribution has fractional power at $\ell =10$ of $f_{10}=0.01$.

Figure 2

68% and 95% contours of the marginalized 2D posterior distribution for a cosmological model with (a) $r=0.04$ and no string component, (b) $r=0.04$ and $f_{10}=0.008$, and (c) $f_{10}=0.01$ with no tensor component. The actual models are depicted with a cross.

Figure 3

Marginalized 1D distribution (a) for $f_{10}$ obtained for a fiducial model with $r=0.04$ and no string component (b) for $r$ obtained when the fiducial model has an $f_{10}=0.01$ and no tensors component. The plots show that fitting for only the wrong component does not result in any detection but only upper limits.