Invariant tori for the Hamiltonian derivative wave equation with higher order nonlinearity.

In this paper, we will study the Hamiltonian derivative wave equation with higher order nonlinearity \begin{document}$ y_{tt}-y_{xx}+my+(Dy)^5 = 0, \quad x\in\mathbb{T}: = \mathbb{R}/2\pi\mathbb{Z}, $\end{document} where \begin{document}$ m>0 $\end{document} is a potential and$ D: = \sqrt{-\partial_{xx}+m}. $We will prove that, for any integer \begin{document}$ b\geq2 $\end{document}, the above equation admits many small amplitude quasi-periodic solutions corresponding to \begin{document}$ b $\end{document}-dimensional invariant tori of an associated infinite dimensional Hamiltonian system. The proof is based on infinite dimensional KAM theory and partial Birkhoff normal form. [ABSTRACT FROM AUTHOR]