Heteroclinics for non-autonomous second-order differential equations

Abstract

We investigate new conditions for the existence of heteroclinics connecting $\pm 1$ for a non-autonomous equation of the form \begin{equation} \label{hetero} \ddot u=a(t)f(u) \end{equation} where $a(t)$ is a bounded positive function and $f(\pm 1)=0$. Here $f=F'$, where $F$ is a $C^1$ non-negative function such that $F(-1)=F(1)=0$. We are interested mainly in the case where $a(t)$ approaches its positive limit, as $|t|\to\infty$, from above, but we allow also the (``asymptotically asymmetric") case where $|\lim _{t\to-\infty}a(t)-\lim _{t\to+\infty}a(t)|$ is a sufficiently small positive number. Variational methods are used in the proofs.