Quadratic-inflation amplitude calibration
= Quadratic-inflation amplitude calibration
{title2=$m/M_{\rm pl}=\sqrt{24\pi^2A_s}/(2N+1)$}
For a quadratic potential with the end set by $\epsilon_V=1$, a mode leaving $N$ e-folds earlier has $\phi_*^2=(4N+2)M_{\rm pl}^2$. Its curvature amplitude is $(m/M_{\rm pl})^2(2N+1)^2/(24\pi^2)$. Thus the scalar amplitude fixes the <inflaton> mass while the tilt and tensor ratio depend only on the exit e-fold count at this order.