= COBE normalization of quartic hilltop inflation
{c}
{title2=$\alpha=\pi^2\mathcal P_{\mathcal R}/(8N^3)$}
For a negligible tensor contribution, the historical COBE horizon amplitude $\delta_H\sim2\times10^{-5}$ corresponds to curvature power $\mathcal P_{\mathcal R}\sim25\delta_H^2/4$. In <quartic hilltop inflation>, $\alpha=\pi^2\mathcal P_{\mathcal R}/(8N^3)$ is of order $10^{-14}$ at $N=50$, independent of the small symmetry-breaking scale at this order. The exact inferred amplitude depends on the late cosmology and tilt used in the COBE transfer calculation.
// Target: cosmic-inflation.bigb
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