Quadratic-potential slow-roll solution
= Quadratic-potential slow-roll solution
For $V(\phi)=m^2\phi^2$ in units where $3H^2\simeq V$ and for positive $\phi$,
$$
\phi(t)=\phi_i-\frac{2m}{\sqrt3}t,
$$
and
$$
a(t)=a_i\exp\left(
\frac{m\phi_i}{\sqrt3}t-\frac{m^2t^2}{3}
\right)
=a_i\exp\left(\frac{\phi_i^2-\phi(t)^2}{4}\right).
$$