= Solution
The <single-field inflation squeezed-limit consistency relation> for the <comoving curvature perturbation> is
$$
\boxed{\lim_{q\to0}
B_{\mathcal R}(q,k,|\mathbf k+\mathbf q|)
=-(n_s-1)P_{\mathcal R}(q)P_{\mathcal R}(k)}.
$$
Equivalently, $B_{\mathcal R}/P_{\mathcal R}(q)=-(3+k\partial_k)P_{\mathcal R}(k)$. The scalar shift in parts a--c is an internal symmetry and leaves the hard fields unchanged, so its right-hand side vanishes. A long adiabatic curvature mode instead acts as a spatial dilation of the hard coordinates, and its response is the scale dependence measured by the <scalar spectral index>.
Back to article page
