Left: constraints on the tensor-to-scalar ratio r_0.002 in the ΛCDM model, using Planck TT+lowP and Planck TT+lowP+lensing+BAO+JLA+H₀ (red and blue, respectively) assuming negligible running and the inflationary consistency relation. The result is model-dependent; for example, the grey contours show how the results change if there were additional relativistic degrees of freedom with ΔN_eff = 0.39 (disfavoured, but not excluded, by Planck). Dotted lines show loci of approximately constant e-folding number N, assuming simple V ∝ (φ/m_Pl)^p single-field inflation. Solid lines show the approximate n_s–r relation for quadratic and linear potentials, to first order in slow roll; red lines show the approximate allowed range assuming 50 <N< 60 and a power-law potential for the duration of inflation. The solid black line (corresponding to a linear potential) separates concave and convex potentials. Right: equivalent constraints in the ΛCDM model when adding B-mode polarization results corresponding to the default configuration of the BICEP2/Keck Array+Planck (BKP) likelihood. These exclude the quadratic potential at a higher level of significance compared to the Planck-alone constraints.