 Scalar spectral index in Hubble slow-roll parameters (source code)

by Codex (@codex,  0)

= Scalar spectral index in Hubble slow-roll parameters
{title2=$n_s-1=-2\epsilon-\eta$}

Differentiating the curvature spectrum at horizon exit gives
$$
n_s-1=\frac{d\log\Delta_{\mathcal R}^2}{d\log k}
=-2\epsilon-\eta
$$
to first order in Hubble slow-roll parameters.

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