= Second harmonic and mean displacement of a weakly cubic oscillator
{title2=$x=A\cos\vartheta-3\lambda A^2/(2m\omega^2)+[\lambda A^2/(2m\omega^2)]\cos2\vartheta$}
With $\vartheta=\omega t+\delta$, a weak cubic potential produces a nonzero mean position and a second harmonic at first order. There is no first-order <frequency> shift. Higher-order <frequency> changes can accumulate <phase> over sufficiently long times, so the first-order expression is not a uniform all-time approximation.
Back to article page
