The marginalized posterior distribution in the ε₁-ε₂ plane for the ΛCDM parameter set extended by allowing for non-zero primordial tensor modes. The dashed lines show the 68 and 95 per cent contours obtained using CMB information alone. The solid contours correspond to the results obtained from the combination of CMB data plus the shape of the CMASS ξ (s). The dot-dashed lines correspond to chaotic inflationary models with p = 1, 2 and 4, as indicated by the labels. The dotted line corresponds to a constant value of N = 60.